Zora & Syspira: wolf-like prowling spiders

Did you ever come across one of the most beautiful wolf spiders you’ve ever seen, only to realize that it’s not a wolf spider at all, because the eyes are all wrong? And if it’s not a wolf spider then what the heck is it because it doesn’t look like a spider from any of the other spider families you’re familiar with? No? Well, I had this experience recently. Twice, actually.

The first time it happened was during our epic journey from Toronto to southern Texas to California and then to Victoria (also known as #SpiderTrip2016 – check out some of the great photos Sean took along the way here). We stopped one morning in Joshua Tree National Park and flipped over some rocks to see if we could find any insects or spiders hiding underneath. Almost immediately, I uncovered this gorgeous spider with perfect desert camouflage.

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Not a wolf spider. Photo: Sean McCann.

The bold markings reminded me a bit of some funnel-web weavers in the family Agelenidae, but this spider didn’t have a web.

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Agelenopsis aperta (family Agelenidae, the funnel-web weavers). Yeah, this spider isn’t on a web either, but that’s because we put it on a rock to get a good photograph of it. Agelenids are usually pretty camera-shy, and they like to hide in their retreats. Photo: Sean McCann.

The sandy camouflage was similar to that of the beach-dwelling wolf spider Arctosa perita, but on closer inspection I realized the eyes were all wrong for it to be a lycosid.

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Arctosa perita, with characteristic wolf spider eye arrangement. Photo: Sean McCann.

The key to figuring out whether or not you’ve got a wolf spider is the eye arrangement. Lycosids are visual hunters that have their eyes arranged in three rows. The first row has four small eyes, the second has two large forward-facing eyes, and the third has another pair of slightly smaller eyes quite far back on the cephalothorax. From straight on, they may appear to have only 6 eyes (the first two rows).

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Wolf spider (family Lycosidae) eye arrangement. Photo: Sean McCann.

Syspira is clearly not a wolf spider – it has two rows of four eyes (or if you like, a smiley face eye arrangement – once you see it, you won’t be able to un-see it!) that are all pretty similar in size.

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From above, the eyes appear to be arranged in two more or less straight rows.

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I never would have guessed by looking at it that this spider is in fact a prowling spider in the family Miturgidae. When I think of miturgids, the first thing that comes to mind are the long-legged sac spiders in the genus Cheiracanthium.

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Cheiracanthium sp. – a yellow sac spider in the family Eutichuridae (formerly placed in Miturgidae, and before that, Clubionidae – spider systematics is complicated and constantly changing). Photo: Sean McCann.

These “yellow sac spiders” are famous for being common in homes, biting people all the time (actually, they rarely bite) and causing necrosis (they don’t, although bites are painful like a bee sting), and causing car trouble. They also aren’t actually in the family Miturgidae. They used to be, but they recently got separated into a new family called Eutichuridae, so I really need to update my mental inventory of spider families! Anyway, because the spider we found didn’t look at all like a long-legged sac spider, I didn’t think of looking in the family Miturgidae. It was only later that I was browsing Marshal Hedin’s wonderful collection of spider photographs on entirely unrelated business that I came across this photograph:

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Immature Syspira sp. (family Miturgidae, also known as the prowling spiders). Photo: Marshal Hedin. Licensed under CC BY-SA 2.0.

That’s it! That’s our spider! Not only does it look pretty much identical, but it was found in the very same desert where we found ours. Syspira! The trail goes cold here, however. I can’t say for sure what species it is because the most recent revision of the genus is an unpublished thesis that I can’t get my hands on at the moment (for what it’s worth, I suspect Syspira tigrina). And very little is known about the natural history of these spiders. They are nocturnal wandering hunters who hunker down under rocks or other objects during the heat of the day. They are a pretty good size – the body length (combined length of the two body segments) of the individual we found is probably about 15 mm.

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Female Syspira sp. Photo: Sean McCann.

Our second wolf-like spider is a much smaller critter (less than 5 mm in body length) that we found wandering the forest floor while we were hiking at Mount Work on southern Vancouver Island this past weekend.

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Wolf-like spider from Mount Work. Photo: Sean McCann.

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This photo shows how tiny this spider is relative to Sean’s thumbnail. Photo: Sean McCann.

This little guy definitely had us thinking he was a wolf spider until we took a closer look at his eyes. The eye pattern is sort of similar to that of a lycosid, but I only see two rows of four eyes rather than three distinct rows, and the middle two eyes in the second row (called the posterior median eyes if you want to be technical) are too close together. This eye arrangement is more similar to that of ctenids (wandering spiders, which we don’t have in Canada) or pisaurids (nursery web spiders and fishing spiders).

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Eye arrangement of our mystery spider. Photo: Sean McCann.

I guessed that this might be Zora hespera (another miturgid!) based on a drawing of a similar tiny spider in our field guide, and our friend and arachnological guru Robb Bennett quickly confirmed the guess. As it turns out, this species was only described in 1991, and Robb first documented its presence in British Columbia in 1996.

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Adult male Zora hespera (Miturgidae). Photo: Sean McCann.

The genus Zora used to be in the family Zoridae, which no longer exists (if you use the excellent Field Guide to the Spiders of California, however, you’ll still find Zora hespera listed as a zorid). The name Zora is also new – the genus was originally called Lycaena (which means female wolf) because of its similarity to wolf spiders, but the name had to be replaced because it was already being used for a butterfly genus. These spiders hunt on the ground and low vegetation during the day and are most often found in open sunny areas of wooded or disturbed habitats.

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Adult male Zora hespera. Note how small he is relative to the pine needles! He was pretty cryptic against the forest floor. Photo: Sean McCann.

The individual we found prowling the forest floor is a male (you can tell by the enlarged pedipalps) who may have been on the hunt for a female. Courtship in this species is brief and includes a leg-waving display on the part of the male. Once mated, the female produces an egg sac that she attaches to the underside of a rock or other object. A flat sheet of silk hides the egg sac and the female stands guard to protect her offspring from predators and parasites.

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Syspira sp. looking cryptic on the desert sand. Photo: Sean McCann.

Spider identification can be tricky! Next time you think you’ve found a wolf spider, take a closer look – it might be a wolf-like prowling spider, or something else altogether! The more time I spend learning about spiders, the more amazed I am by their beauty and diversity.

References

Adams, R. J. (2014). Field Guide to the Spiders of California and the Pacific Coast States (Vol. 108). University of California Press.

Bennett, R. G., & Brumwell, L. J. (1996). Zora hespera in British Columbia: a new spider family record for Canada (Araneae: Zoridae). Journal of the Entomological Society of British Columbia, 93, 105-110. PDF

Bradley, R. A. (2012). Common Spiders of North America. University of California Press.

Corey, D. T., & Mott, D. J. (1991). A revision of the genus Zora (Araneae, Zoridae) in North America. Journal of Arachnology, 55-61. PDF

Ubick, D., Paquin, P., Cushing, P., & Roth, V. (2005). Spiders of North America – an identification manual. American Arachnological Society.

Rhomphaea: ridiculously long theridiids

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Male Rhomphaea fictilium – a theridiid with a ridiculously long abdomen and pedipalps! Photo: Al Denesbeck (used with permission).

I’ve written about long spiders before: the “stretch spiders” in the family Tetragnathidae (long-jawed orb-weavers) are notable for their elongated bodies as well as their long jaws. When I first spotted Rhomphaea, I thought it might be a tetragnathid, before taking a closer look and realizing it must be something else entirely. As it turns out, Rhomphaea is a very odd-looking member of the family Theridiidae, or comb-footed spiders, which includes the black widows!

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Rhomphaea fictilium from my field site at Island View Beach on Vancouver Island, BC. This spider does not show much resemblance to its relatives the black widows, who are found nearby! Photo: Sean McCann (used with permission).

Rhomphaea is a Latin word of Thracian origin that literally means long spear or javelin. The long, straight abdomen of the male in the photo below helps explain the name.

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Male Rhomphaea fictilium with long, “spear-like” abdomen and extremely long pedipalps. Photo: Kyron Basu, licensed under CC BY-ND-NC 1.0.

Below is a female Rhomphaea projiciens with her egg sac. Note that the spider has a tiny spine on the end of her abdomen, making it more literally spear-like!

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Rhomphaea prociciens female with egg sac. Photo: Jon Hart (used with permission).

My first encounter with this genus was observing Rhomphaea fictilium. Fictilis means “clay” in Latin, and the Latin-derived English adjective fictile “means capable of being molded.” The abdomens of Rhomphaea fictilium are worm-like and flexible, allowing the spider to change its shape. This ability may help Rhomphaea to camouflage itself in different contexts – the shortened abdomen of the little one in the photo above helps it to blend in with the seed heads it rests on. When their abdomens are held out long and straight, these spiders can look like very convincing sticks. The incredible photo below shows an individual that looks like it has the tail of a (very tiny) dragon!

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Rhomphaea fictilium with extended abdomen (dragon’s tail?). Photo: Gergin Blagoev, licensed under CC BY 3.0.

As well as having wonderfully strange morphology, Rhomphaea have rather unusual habits. Most spiders are generalist predators, and spiders in the family Theridiidae typically build tangle webs that they use to catch crawling insects and other arthropods, including other spiders. Rhomphaea, unlike most of their relatives, specialize on hunting other spiders. They do sometimes build their own rudimentary webs from just a few silk lines, but they also enter the webs of other spiders and use aggressive mimicry to hunt their owners. Rhomphaea will pluck the web and produce vibrations that lure the resident spider out to investigate what they perceive to be prey caught in the web. The web-building hunter then becomes the hunted, tricked into the approaching the dangerous intruder. Rhomphaea fictilium have been reported to prey on other theridiids, orb-weavers (araneids), sheet-weavers (linyphiids) and others.

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Rhomphaea fictilium with its unfortunate prey. Note that the spider is covered with silk – theridiids comb sticky silk out of their spinnerets with their fourth legs and throw it over their victims to subdue then before biting. Photo: Al Denesdbeck (used with permission).

These tiny, cryptic spiders are rare and difficult to spot, but keep your eyes out for them in low tree branches, grasses, and bushes – or in the webs of other spiders!

References & further reading

Bradley, R. A. (2012). Common Spiders of North America. Univ of California Press.

Exline, H., & Levi, H. W. (1962). American spiders of the genus Argyrodes (Araneae, Theridiidae). Arañas americanas del género Argyrodes (Araneae, Theridiidae). Bulletin of the Museum of Comparative Zoology., 127(2), 75-202. Full text at BHL

Paquin, P., & Dupérré, N. (2001). On the distribution and phenology of Argyrodes fictilium (Araneae, Theridiidae) at its northern limit of North America. Journal of Arachnology, 29(2), 238-243. PDF

 

Oecobiidae

Last week a colleague of mine found a tiny spider we didn’t recognize in the biology building at UTSC. We regularly find common house-dwelling spiders in and around the buildings on campus (most often false widows, Steatoda grossa triangulosa). But this spider was different from the ones we usually find in the building – tiny (only a couple of millimetres long), pale in colour, and a very fast runner! I brought it home and asked Sean to take some photos of it, and we soon realized it was a member of the fascinating family Oecobiidae. [note: this paragraph was revised on 7 Dec. 2015]

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Oecobius sp. from Scarborough, Ontario. Photo: Sean McCann (used with permission)

The name Oecobiidae comes from the Greek words oikos (οικος), meaning “house” and bios (βιος), meaning “living”. A name that means “living in the house” is highly appropriate for these synanthropic spiders that are commonly found in human dwellings. The spider we found is most likely one of two species that have a worldwide distribution and can be found in southeastern Canada: Oecobius cellariorium (cellariorium means, unsurprisingly, “of the cellar” in Latin) and Oecobius navus (navus means active or busy, which these little spiders certainly are!).

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Oecobiid next to its sheetweb. Photo: Mark Yokoyama, licensed under CC BY-NC-ND 2.0

Despite their very appropriate scientific names, non-Latin and Greek speakers have come up with a variety of fun common names for members of this family. These include wall spiders, baseboard spiders, stucco spiders, starlegged spiders, disc web spiders, and dwarf round-headed spiders. The official common name for the family is “flatmesh weavers” (at least in North America, according to the American Arachnological Society) because of the flat webs they build.

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Figures 2 and 3 from Glatz 1969, showing the two kinds of webs built by Oecobius navus (previously called Oecobius annulipes). The first is a “star-shaped” web with an upper and lower sheet surrounded by radiating silk lines. These threads allow the spider sitting on the lower sheet to detect vibrations produced by prey. When the spider detects prey outside its web it can rush out in any direction to capture it. The second type of web is similar, but the upper and lower sheets form a tube, with only two entrances.

I quite like the name starlegged spiders for oecobiids though, because it so aptly describes one of the very distinctive characteristics of spiders in this family. Unlike most spiders, which have the first two pairs of legs pointing forward and the last two pointing backward (an exception is the family Segestriidae, which have the first three pairs pointing forward), oecobiids have all 8 legs sticking more or less straight out from their bodies, in a somewhat starburst-like fashion.

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Oecobius sp. (male). In addition to being “star-legged”, oecobiids have their 8 eyes arranged in a characteristic cluster in the centre of a circular cephalothorax. Photo: Sean McCann

The defining characteristic of oecobiids, however, is the extraordinary anal tubercle (that’s exactly how it’s described in this paper, and I assure you it is entirely appropriate). Seriously, these tiny spiders have the most incredible hairy butts! Ahem. Fringed anal tubercles, I mean. Let me explain.

The North American oecobiids are cribellate spiders. What this means is that the spider is equipped with a cribellum (a special silk spinning organ covered with thousands of tiny spigots) near the spinnerets and a calamistrum (a specialized row of bristles) on each of the fourth legs. The calamistrum is used to comb out fine strands of cribellar silk into sheets with a fuzzy texture. The stickiness of this silk comes from its physical structure, as opposed to the glue used by ecribellate (non-cribellate) spiders to make their capture silk sticky. Anyway, instead of combing silk out of the cribellum with the calamistrum like regular cribellate spiders, oecobiids have their own fancy way of doing things. They use the fringe of hairs on their jointed anal tubercles to comb silk directly from arrays of spigots on a pair of enlarged spinnerets.

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Figure 11 from Glatz 1969, showing the extraordinary fringed anal tubercle and spinning apparatus. The long posterior lateral spinnerets (labelled hspw) are covered with spigots (s). The outer fringe of hairs (rh) on the anal tubercle comb silk out of the spinnerets. The anal tubercle is also equipped with sensory hairs (mh) that are used to detect prey movement via vibrations through the silk threads.

This unusual set-up enables oecobiids to produce a sheet of sticky silk without using their legs, which is important for their unusual method of prey capture. Many spiders use their last pair of legs to pull sticky silk out of their spinnerets and throw it onto their prey. Oecobiids, instead, run around and around their prey in circles as they spew out ribbons of silk from their feathery butts. Once the victim (often an ant) is fully encircled and stuck to the substrate, the spider bites it. Here is a video of the behaviour. (Video* by Ahmet Özkan, used with permission.)

As you can see in the video, the spider does occasionally use its last pair of legs while wrapping the ant with silk, but the anal tubercle/spinneret combo does most of the work. Female and juveniles of Oecobius navus can produce cribellar silk, but adult males have a reduced cribellum and don’t have a calamistrum at all. Another oecobiid genus, Uroctea, used to be placed in its own family, the Urocteidae, because they are ecribellate (lacking the cribellum and calamistrum).

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Uroctea durandi, one of the ecribelleate oecobiids. Photo: Siga, licensed under CC BY-SA 3.0

Early work on spiders in the genus Oecobius suggested that they were ant-specialists, but more recent research has shown that they eat a variety of prey types. However, different populations of a single species seem to specialize to some extent on whatever type of prey is most locally abundant. In Portugal, a population of Oecobius navus preys mainly on ants, but another population in Uruguay eats mostly flies.

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Male (right) and female (left) Oecobius sp. Photo: Allan Lance (used with permission). Check out more of Allan’s photos of oecobiids here.

Reproductive behaviour has only been well documented in Oecobius navus. The male spins a tubular silk mating web on top of the female’s retreat and tries to entice her to join him inside. Copulation only occurs if she enters the male’s web, and sometimes the female will cannibalize the male during or after mating. Females are not caring mothers in this species – they spin several egg sacs that each contain only 3 to 10 eggs and then abandon them.

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Oecobius sp. from Scarborough. Photo: Sean McCann

Now that you know all about oecobiids, keep your eyes out for them! They live all over the world, and often on the walls and ceilings of houses. You never know – there might be one in the room with you right now!

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This photo of an Oecobius sp. is one Sean dug up from his archives. We had found the spider in our old lab at SFU in BC, and did not identify it at the time. When Sean showed me the photo recently, and I started trying to ID it, I took a look at the checklist of BC spiders to get an idea of which species it might be. I didn’t see any oecobiids on the list, so I emailed the author, Robb Bennett, and it turns out that this photo is the first record of the family for British Columbia.

*For another cool oecobiid video with a surprise ending, click here.

References

Adams, R. J. (2014). Field Guide to the Spiders of California and the Pacific Coast States (Vol. 108). Univ of California Press.

Glatz, L. (1967). Zur biologie und morphologie von Oecobius annulipes lucas (Araneae, Oecobiidae). Zeitschrift für Morphologie der Tiere, 61(2), 185-214.

Líznarová, E., Sentenská, L., García, L. F., Pekár, S., & Viera, C. (2013). Local trophic specialisation in a cosmopolitan spider (Araneae). Zoology, 116(1), 20-26.

Shear, W. A. (1970). The spider family Oecobiidae in North America, Mexico, and the West Indies. Harvard Univ Mus Compar Zool Bull.

A quick survey

Dear readers,

I’ve teamed up with Science Borealis, Dr. Paige Jarreau from Louisiana State University and 20 other Canadian science bloggers, to conduct a broad survey of Canadian science blog readers. Together we are trying to find out who reads science blogs in Canada, where they come from, whether Canadian-specific content is important to them and where they go for trustworthy, accurate science news and information. Your feedback will also help me learn more about my own blog readers.

It will only take 5 minutes to complete the survey. Begin here:
http://bit.ly/ScienceBorealisSurvey

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This pseudoscorpion reads books because there are lots of delicious booklice to be found between their pages. Why do you read science blogs? [Photo: Sean McCann]

If you complete the survey you will be entered to win one of eleven prizes! A $50 Chapters Gift Card, a $20 surprise gift card, 3 Science Borealis T-shirts and 6 Surprise Gifts! PLUS everyone who completes the survey will receive a free hi-resolution science photograph from Paige’s Photography!

Myrmecophilic spiders

Myrmeco = ant; philic = loving

Note: All photos in this post are copyright Sean McCann.

Yesterday, for the final day of Arachtober, Sean and I went to Tommy Thompson park in Toronto to look for some autumn arachnids and other arthropods. Sean was very excited when he turned over a rock and found a nest of acrobat ants, Crematogaster cerasi. The genus Crematogaster is mainly tropical, and we didn’t have them back in BCso it was a pretty cool find for us.

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Then we took a closer look at the ants running around under the rock. One of these ants is not like the others!

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The interloper is a myrmecophilic spider in the family Phrurolithidae – probably Phruronellus formica. Athough they are not modified to look especially ant-like in shape, their shiny black abdomens certainly help them to blend in with the colony.

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Hey look, there’s another one! Although we were almost fooled by the imperfect ant-mimicry of these spiders, ants rely much more on smell and touch than vision, so looking a bit ant-like wouldn’t do much to help them fit in. It may, however, provide some protection against predators that find ants distasteful or difficult to eat.

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Not much is known about their natural history, but Phruronellus formica is thought to be an obligate associate of ants in the genus Crematogaster [1,2]If they are disturbed, they disappear into the ants’ nest. This implies that the spiders are not only not recognized as intruders by the ants, but are tolerated by their hosts. Presumably they produce or acquire compounds that allow them to wander freely among the ants, who recognize their nest-mates by their colony-specific chemical profile.

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The relationship between Phruronellus formica and Crematogaster has not been studied, but based on what is known about other spider-ant associations [2,3], we can infer a bit about how this arrangement benefits the spiders. Living amongst ants can provide spiders with a comfortable home, free food, and protection from enemies. Myrmecophilic spiders are known to prey on other ant-associates (like collembolans), prey brought back to the colony by their ant hosts, or even the ants themselves. Ants are also fierce defenders, armed with stings or noxious defensive chemicals to protect the colony (and, incidentally, the spiders within it) from predators.

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This doesn’t seem like a very good deal for the ants – at best, the spiders have no effect on them, and at worst, they are stealing food or preying on their hosts or their beneficial symbionts [3]. But the number of spiders in any colony is so small (we saw two among hundreds of ants, in a colony that probably has about 2000 workers) that they are probably not harmful enough to make it worth the ants’ while to do anything about them.

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References: 

1. Emerton, J. H. 1911. New spiders from New England. Trans. Connecticut Acad. Arts and Sciences 16: 383-407. full text

2. Cushing, P. E. (1997). Myrmecomorphy and myrmecophily in spiders: a review. Florida Entomologist 165-193. PDF

3. Cushing, P. E. (2012). Spider-ant associations: an updated review of myrmecomorphy, myrmecophily, and myrmecophagy in spiders. Psyche: A Journal of Entomology.  doi:10.1155/2012/151989

 

Pirate spiders

Mimetidae are the pirates of the spider world, but their acts of theivery take place on the webs, rather than ships, of other spiders. The name Mimetidae means “imitator” and is thus a very fitting name for these sneaky spiders.

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A mimetid found at Payne’s Prairie in Florida. Photo: Sean McCann (used with permission).

Common names for this family include pirate spiders and cannibal spiders, for reasons that will soon become clear. They have a worldwide distribution, occurring on every continent except Antarctica, and everywhere in North America except the arctic.

What makes mimetids so fascinating is their predatory behaviour. These spiders don’t build their own webs. Instead, they invade the webs of other spiders – most often spiders in the families Araneidae (orb-weavers), Theridiidae (cobweb weavers), and Dictynidae (mesh web weavers). Here’s a series of photographs showing an interaction between a pirate spider and an orb-weaver in Arizona. (Full disclosure: Sean and I introduced the mimetid ourselves, hoping to witness a predation event).

Below is the web of a trashline orbweaver, Cyclosa turbinata (family Araneidae). The vertical “trashline” that bisects the upper half of the orb is made of old prey carcasses.

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This photo and the rest in this series by Sean McCann.

Here’s a closer look at the trashline. The spider is well camouflaged when she sits right in the centre of the orb-web.

CyclosaHere’s a better view of the spider herself.

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And this is another Cyclosa conica female, for a better idea of what these spiders look like.

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Ok, now back to the pirate spider! This is a male Mimetus hesperus that we found nearby, and introduced onto the yucca right next to the orb-web.

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Soon he entered the periphery of the web and assumed the ‘legs cocked’ posture characteristic of hunting mimetids. He then started carefully plucking the threads of the orb-web with his front pair of legs. This plucking makes the web vibrate in very much the same way it would if an insect had been captured, and resulted in the Cyclosa female orienting toward the source of the vibrations, but remaining in the hub of the web.

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Gradually Mimetus began to move toward the hub of the orb-web, plucking and sometimes even snapping spiral threads (much as would happen if a winged insect was struggling to free itself from the sticky threads). At first it seemed the mimetid was going to be successful in luring the female Cyclosa out onto the web and into its deadly embrace, but after a few steps toward the mimetid she suddenly dropped out of the web on a dragline.

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As Cyclosa hung below, the mimetid made his way to the hub of the web and took up residence. Sean and I were impressed by Cyclosa’s ability to recognize the mimetid as as being dangerous rather than dinner, but disappointed not to see Mimetus succeed in securing a meal. So we put the spider back onto her web. (Sorry Cyclosa!)

As soon as she started moving back toward the hub, Mimetus lunged and bit Cyclosa. Mimetids are equipped with a spider-specific venom that paralyzes their prey almost instantly.  

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The successful pirate then carried its meal back to the periphery of the web to feed. Below you can see that he has Cyclosa by the leg. Apparently mimetids almost always bite the legs of their victims, and when they do paralysis occurs within moments. If they bite another spider’s abdomen, however, the venom takes much longer to work. 

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We left the pirate enjoying his meal on the yucca. He may have gone on to find a new web to invade, or taken over Cyclosa’s web for a while. If we hadn’t interfered, he may have remained in the hub of the web and used it to capture insect prey himself. In addition to this sort of takeover, mimetids are also known to steal prey from the webs of other spiders who are much larger (and thus too big to prey on). They also sometimes eat the eggs of other spiders.

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Mimetus sp. from High Park in Toronto, Ontario. Photo: Sean McCann (used with permission).

Notes on identification:

Mimetids look most similar to orb-weavers (araneids) and cobweb weavers (theridiids) but they can be distinguished from spiders in all other families by the unique pattern of spines on their first two pairs of very long legs.

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Nice example of the characteristic spination on the tibiae and tarsi (first two leg segments) of the first two legs of pirate spiders. Photo: Nicky Bay (used with permission). Check out more of Nicky’s awesome pirate spider photos here.

The eye arrangement is not so diagnostic (it’s quite similar to that of araneids and theridiids) but here’s a great portrait courtesy of the Insects Unlocked project.

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Finally, Mimetids build characteristic egg sacs that are easy to identify to genus even in the absence of the mother (who inevitably abandons her offspring). The sac has a long thin stalk and/or a fluffy coating, depending on the genus, and these two features may help protect the eggs within from parasitoids or predators.

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Egg sac of a mimetid in the genus Ero, found hanging inside a hollow stump in Burns Bog, Delta, BC. Photo: Sean McCann (used with permission)

References and further reading:

Eric Eaton’s blog post on pirate spiders.

Africa Gomez’s blog post on pirate spiders.

Bristowe, W. S. (1958). The world of spiders. London: Collins.

Jackson, R. R., & Whitehouse, M. E. (1986). The biology of New Zealand and Queensland pirate spiders (Araneae, Mimetidae): aggressive mimicry, araneophagy and prey specialization. Journal of Zoology, 210(2), 279-303.

Kloock, C. T. (2001). Diet and insectivory in the “araneophagic” spider, Mimetus notius (Araneae: Mimetidae). The American Midland Naturalist, 146(2), 424-428.

Kloock, C. T. (2012). Natural History of the Pirate Spider Mimetus hesperus (Araneae; Mimetidae) in Kern County, California. The Southwestern Naturalist,57(4), 417-420.

Opportunity makes a thief

Sometimes unexpected things happen when you’re observing spiders. The following series of photos is by Catherine Aitken, who has a wonderful wildlife photography blog: Lardeau Valley Time. She recently witnessed and captured this incredible interaction in her garden, and kindly gave me permission to share her photos here.

Here we see a lovely pink and white flower crab spider (Misumena vatia) peacefully slurping her lunch (an unfortunate hoverfly).

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Photo: Catherine Aitken (used with permission).

But soon an uninvited guest (a foraging western yellowjacket) arrives.

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Photo: Catherine Aitken (used with permission).

A great struggle ensues.

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Photo: Catherine Aitken (used with permission).

The wasp emerges victorious, while the spider retreats.

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Photo: Catherine Aitken (used with permission).

Crab spiders are pretty formidable predators, and I’ve seen them feeding on yellowjackets themselves, as in the photo below. So I found this instance of a wasp stealing a crab spider’s prey rather surprising and fascinating. You never know what wonders you might witness when you spend time watching spiders!

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Xysticus with eastern yellowjacket. Photo: Sean McCann (used with permission).

Castianeira: ant-like spiders

The spider genus Castianeira (in the family Corinnidae) is one of my favourites. These small spiders are rather elusive, but so beautiful! There are currently 128 known species in the genus, so I will only be able to highlight a small number in this post. This should nonetheless provide a glimpse into the diversity of gorgeous forms they take!

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Castianeira dorsata from Arizona. Photo: Sean McCann

Natural History

Common names for the family Corinnidae include “ground sac spiders” (they used to be included in the sac spider family Clubionidae) and “antmimic spiders”. They are not all antmimics, but many species in the genus Castianeira are rather ant-like and are considered generalized ant-mimics.

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Castianeira longipalpa, found under a rock near a lot of ants at Iona beach in Richmond, British Columbia. This species is thought to be a generalized mimic of myrmecine or ponerine ants. Photo: Sean McCann

The species shown above and below don’t look especially like any particular species of ant, and their mimicry is “imperfect” – besides having fairly elongate bodies and stripes that might give the illusion of a third body segment, they look a lot more like spiders than ants. At first glance, however, they can easily be mistaken for ants (at least by humans). They are fairly ant-like in size and colour (often red or brown and/or black) and they move around a lot like ants, waving their front legs like antennae, and bobbing their abdomens in ant-like fashion. These spiders are often found in close proximity to ants, which provides some support for the idea that they are in fact mimics. They might benefit by looking ant-like to predators who find ants distasteful (and don’t look too closely).

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Castianeira sp. from near the Soutwestern Research Station in Arizona. Photo: Sean McCann

Some species, like the one from Singapore below, are a little more ant-shaped, but their morphology is not as extremely modified as some other kinds of ant-mimicking spiders (like this one photographed by Alex Wild).

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Castianeira sp. from Singapore. Photo: H. K. Tang, licensed under CC BY-NC-ND 2.0.

Some Castianeira species are thought to mimic velvet ants (Mutillidae), rather than ants. Mutillids are not actually ants but wasps, and the females are wingless and brightly coloured, with extremely painful stings. In this case, harmless Castianeira spiders might benefit by looking like the much more dangerous velvet ants, and thus be avoided by predators (this is called Batesian mimicry).

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Castianeira occidens from South Fork, Arizona. This spider was found running (fast!) across a forest path during the day. Photo: Sean McCann

As with the ant-like species, these spiders tend not to look very much like any particular species of velvet ant. They are generally mutillid-like in their movements and in that they have bright markings on their abdomens reminiscent of the warning colouration (aposematism) of velvet ants, like the one below.

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Velvet ant from French Guiana. Photo: Sean McCann.

One of the most gorgeous spiders I have ever seen is the Castianeira dorsata (below, and at the top of this post) that Sean found wandering around by a stream one evening while we were staying at the Southwestern Research Station in Arizona. These spiders are supposed to be active during the day, so it was interesting to find this one running around in the dark while we were out with our headlamps searching for wolf spiders. Obviously, looking like a velvet ant isn’t going to fool anyone if it’s so dark they can’t see how brightly coloured you are.

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Castianeira dorsata from Arizona. Photo: Sean McCann

I don’t know of any velvet ants that look much like this (although many are bright orange), but I just can’t get over how beautiful this spider is with its sunset-like stripes on the abdomen and a bluish iridescence on the carapace. Even more dramatic is what I like to call the “tiger-striped” Castianeira below. The photo below shows the relative size of Castianeira amoena on a human hand. I imagine they would be as fearsome or even more so than a tiger if they were blown up to a comparable size. In reality however, these spiders are extremely shy, and very fast runners when they are disturbed (as by humans!) – so all the photographs in this post are real treasures.

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Castianeira amoena. Photo: promiseminime, licensed under CC BY-NC-ND 2.0.

Finally, the spider below is notCastianeira, but a species in the related genus Graptartia (also in the subfamily Castianeirinae). I couldn’t resist adding it because it shows such a beautiful example of mimicry, and one that’s much more specific than the examples above. The velvet ant model and spider mimic where found within a few metres of another (one of the criteria for Batesian mimicry is that the model and mimic have to be found in the same place!) and the photographer then managed to move them so that he could capture them together in the photo below. Wow!

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Graptartia granulosa mimic and velvet ant model from Tanzania. Photo: Paul Bertner (used with permission).

Notes on Identification

Usually these spiders are pretty recognizable because of their distinctive colouration, but some of the less bold ones can be confused with other ant-like spiders (like Micaria). Spiders in the genus Castianeira have 8 eyes in 2 rows. The posterior eye row (the upper row, in the photo below) is slightly wider than the anterior (lower) row with all four eyes about the same size. Both rows are slightly procurved (curved toward the front end of the spider). The anterior median eyes (front and centre) can be slightly smaller to much larger than the other two in their row.

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Castianeira cingulata portrait, showing the eye arrangement. Photo: sankax, licensed under CC BY-NC 2.0.

The last (hindmost) pair of legs is always longest, followed by the first (frontmost) pair, and the abdomen is often decorated with bands of white scale-like setae (hairs).

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Dorsal veiw of Castianeira longipalpa from BC. Photo: Sean McCann.

 

References:

Dondale, C. D., & Redner, J. H. (1982). The insects and arachnids of Canada. Part 9. The sac spiders of Canada and Alaska. Araneae: Clubionidae and Anyphaenidae (No. 1724).

Reiskind, J. 1969. The spider subfamily Castianeirinae of North and Central America (Araneae, Clubionidae). Bull. Mus. Comp. Zool. 138(5): 163-325.

Segestriidae: tube web spiders

Recently Sean and I took a quick trip down to Bellingham, Washington, to meet up with a friend. While we were wandering around a beachfront park, we encountered this beautiful spider under the loose bark of a tree. I didn’t recognize it, and we didn’t have our field guide with us, so it wasn’t until we got home that we were able to identify it as Segestria pacifica – a member of the tube web spider family Segestriidae.

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Segestria pacifica. This species is the one member of the family Segestriidae that can be found in British Columbia, but we’ve never encountered it before. (Photo: Sean McCann)

Segestriids are closely related to spiders in the family Dysderidae (which includes the common woodlouse hunter, Dysdera crocata). Like dysderids, segestriids have only 6 eyes. You can see the characteristic eye arrangement in the photo below – it looks like the pair of eyes that should be at the front and centre of the spider’s face are missing.

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Nice portrait of Segestria pacifica showing the eye arrangement and hairy chelicerae. (Photo: Kyron Basu, licensed under CC BY-ND-NC 1.0)

Spiders in this family also have the unusual habit of resting with their first three pairs of legs pointing forward and the last pair pointing back (most spiders do two pairs pointing forward and two pairs pointing back).

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Segestria pacifica resting in the characteristic pose with six legs forward, two legs back. (Photo: Sean McCann)

Segestria florentina (sadly not found in North America) has beautiful irridescent green chelicerae. The function of this striking colouration is not clear – it’s unlikely to be for catching the eye of a potential mate, because these spiders have poor vision and rely mainly on vibratory and acoustic communication. What we do know is that this structural colour is produced by parallel layers of chitin that reflect different wavelengths of light (called a multilayer reflector). The mechanism is the same one that gives these beautiful beetles their green irridescence.

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Segestria florentina female showing off her beautiful irridescent green chelicerae (Photo: Luis Miguel Bugallo Sánchez, licensed under CC BY-SA 2.5 ES)

Segestriids are nocturnal and build their tube webs in crevices, often in the cracks of rock walls, under loose tree bark, or in the ends of broken branches. Several signal threads are arranged radially around the opining of the tube-web. The hunting spider sits near the entrance of the tube, waiting for prey to make contact with one of her trip lines. This contact transmits vibrations through the silk to the spider’s sensitive feet, six of which rest near the opening of the web, allowing her to determine the exact location of the prey.

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Tube-web of Segestria senoculata (Photo: Totodu74, licensed under CC BY-SA 3.0)

“Corolla spiders” in the genus Ariadna live in the Namib Desert, and have modified their tube webs to include a circle of stones around the entrance. Here the trip lines are very short, and are all attached to the small stones circling the web entrance. The function of the stones is essentially the same as the silk signal lines of a regular tube web, which would not be very effective in the desert because of the constantly shifting sands and gravel. The stone circle solves this problem. When prey brushes against one of stones in the circle, vibrations are transmitted to the spider and it rushes out to dispatch them. The corolla spiders apparently preferentially select quartz crystals for their signal stones – these may direct vibrations from prey more effectively than other kinds of stones.

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Fig. 1 from Henschel (1995) showing the stone circle built by corolla spiders in the Namib desert. The drawing shows the position of the six forward-facing legs of the hunting spider resting just inside the mouth of the burrow.

Females in this family don’t build a traditional egg sac but deposit a mass of eggs in the tube web and then cover them with silk. Very little else seems to be known about the natural history of these spiders, although apparently they are quite easy to keep in captivity, and females can live for several years.

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References:

Adams, R. J. (2014). Field Guide to the Spiders of California and the Pacific Coast States. University of California Press.

Henschel, J. R. (1995). Tool use by spiders: stone selection and placement by corolla spiders Ariadna (Segestriidae) of the Namib Desert. Ethology, 101(3), 187-199.

Ingram, A. L., Ball, A. D., Parker, A. R., Deparis, O., Boulenguez, J., & Berthier, S. (2009). Characterization of the green iridescence on the chelicerae of the tube web spider, Segestria florentina (Rossi 1790) (Araneae, Segestriidae)Journal of Arachnology, 37(1), 68-71.

 

Web reduction for rival obstruction!

This post is about a new paper just published online in the journal Animal Behaviour, titled Web reduction by courting male black widows renders pheromone-emitting females’ webs less attractive to rival males by Catherine Scott, Devin Kirk, Sean McCann, and Gerhard Gries! You can read the full text here (free access until 28 August, 2015).           All photos and video are copyright Sean McCann

This short video shows a male western black widow engaged in web reduction behaviour – a common element of the complex courtship rituals males perform on females’ webs. You can see him cutting some silk lines, then pulling silk out of his spinnerets with his last pair of legs, wrapping it around a bundled up section of the female’s web.

Web reduction behaviour is somewhat puzzling. This male black widow is attempting to convince a potentially cannibalistic female several times his size to mate with him. Destroying large areas of her home – which she relies on for both prey capture and protection from predators – is not the most obvious approach. So why do males do it (I know, the title of the paper probably gives this one away), and why do females let them?

Before we address the mystery of web reduction, let’s take a step back and set the scene for this story. It’s a pretty juicy one – there’s attraction, courtship, rivalry, and manipulation! Or maybe not manipulation… we’ll see!

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Black widows are sexually dimorphic: the familiar female is on the left, and the much smaller and more brightly coloured male is on the right. My study species is the western black widow, Latrodectus hesperus.

Island view beach, on the Saanich Peninsula of Vancouver Island, BC, is a beautiful place to visit. The site shown below is on the lands of the Tsawout First Nation, who have kindly allowed me to collect spiders and do field work here over the past few years.

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This coastal sand dune ecosystem supports a great diversity of organisms, but the black widows are the dominant web-building spiders. Females build their tangle-webs under the driftwood logs at a density of 2-3 webs per square metre of available habitat. There are many logs on this beach; correspondingly, there is a huge population of widow spiders.

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At our field site, black widows build their webs under driftwood logs – often several females can be found living under a single piece of wood!

Female black widows almost never leave their webs, so when it comes time to mate, they need males to come to them. The solution to this problem comes in the form of pheromones on their silk. These chemical messages are kind of like scent-based personal ads, that provide the male with information about the female’s mating status and whether or not she’s well fed (sexual cannibalism is rare in this species, but starving females will sometimes eat males!).

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If the female’s silk pheromone was actually a personal ad, it might say something like this!

Adult male black widows have only one goal in life: find a female to mate with (and become the father of as many offspring as possible). Once they mature, males stop capturing prey and abandon their webs for a more a nomadic lifestyle. If they detect an attractive female’s pheromone in the air, they follow it to her web.

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A nomadic western black widow male traverses the sand dunes in search of a mate. Note: “pheromone trail” added for dramatic effect.

Once he arrives on the female’s web, the male begins an elaborate courtship display, dancing on the web to transmit vibratory messages (including “male, not meal!”) to the female. It may take many hours of courtship before copulation finally occurs.

male_courtingSoon after he arrives, the male may start to destroy the female’s web. He cuts out sections, bundles them up, & wraps them in his own silk. Males usually reduce the area of the web by about 50%, and gather the destroyed sections up into loose silk-wrapped packages. These can be rope-like (as in the photo at the top of this page) or a tighter ball that has been wrapped extensively by the male like the one below.

silk_ball_smallNow to address our earlier question: why do the males engage in this behaviour? 

Well, black widows are not the only spiders who do web reduction. Other species in the same family (Theridiidae) and others (including Linyphiidae) have similar behaviour. Watson showed in 1986 that web reduction in the sierra dome spider makes the female less attractive to rival males. He concluded that by bundling up the female’s web, the male decreases the surface area from which the silk-borne sex pheromone is released. Some researchers have assumed that it works the same way in other species. Others have suggested that web reduction could function in communication between the male and the female, perhaps improving vibration transmission through the web, or transmitting a male silk pheromone to the female. It could have one or both of these functions in black widows, but until now, no one had ever investigated!

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The sierra dome spider, Neriene litigiosa (family Linyphiidae).

We set out to determine whether web reduction decreases female attractiveness to male black widows in a natural setting. We were pretty sceptical that reducing the web surface area by only about 50% could limit pheromone emission. Usually you have to decrease the dose of a pheromone by an order of magnitude to see any difference in attractiveness. However, males aren’t just bundling up the female’s pheromone-laden silk – they are also adding their own. We thought maybe it could be the addition of the male’s silk (and associated pheromones) that keeps other males away. We designed an experiment to try to find out.

First, we put a bunch of female spiders in cages and allowed them to establish webs. Then we loaded up the cages and took them, and a batch of males, to our field site.

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This is what (part of) a truckload of black widows looks like. Here, my coauthor Devin is loading the cages containing females and their webs into the back of the lab pickup.

Once we got to our field site, we removed the female spiders from their cages (because we wanted to look at the attractiveness of silk only, not the females themselves) and set up four treatments: intact webs, mechanically reduced webs (with half the silk cut out), male-reduced webs (with about half the silk, on average, bundled and wrapped by the males we brought) and empty cages as controls (to confirm that captured males were actually attracted to the silk in the cages, not just wandering randomly).

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Four treatments: intact web, scissor-reduced web (50% of silk removed entirely), male-reduced web (courting males bundling up about 50% of silk on average), and no-web control.

We then turned the cages into traps that would capture any wild males attracted to the silk inside by surrounding them with sticky strips. Then we set the traps out on the beach in groups of four – one for each of the treatments.

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The experimental setup. Each of the four traps contains a different treatment, and the white sticky strips surrounding the cages trap males that are attracted to the silk inside the cage.

We set the traps out at sunset (black widows are nocturnal) and waited to see what would happen. Soon the data started strolling in. We checked the traps every three hours, collecting and preserving any captured males. The sheer number of males out on the prowl was incredible – some webs attracted more than 10 males overnight!

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Close-up of a trap containing a pheromone-laden female’s web, with a male black widow captured outside on the sticky strip.

After 24 hours, just by looking at the vials full of male spiders we had captured, the results were clear (if you want to see statistics, you can read the paper!). Male-reduced webs caught only about one third as many males as intact webs, so web reduction does in fact decrease attractiveness! As we suspected, however, removing half of the silk entirely did not significantly reduce a web’s attractiveness – we captured almost as many males outside scissor-reduced webs as intact webs. (A few spiders got trapped outside the empty control cages – they may have blundered into the sticky strips on their way toward an an attractive web.)

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Beautiful data. It’s not often that the raw data tell the whole story, but here they do!

Evidently, when a male black widow reduces a female’s web, whatever he is doing is much more effective at decreasing its attractiveness than removing half of the pheromone-laden silk entirely. And he’s not actually removing any of the female’s silk – he’s just bundling it up into a ball. There are a couple of potential explanations for how web reduction works. Perhaps the female’s pheromone is not evenly distributed on the web, and the male targets the pheromone-rich silk for web reduction. Then, by wrapping those sections up in his own silk, he creates a barrier that limits the emission of the female pheromone. Another possibility is that the male’s silk has its own pheromone on it, one which other males detect and avoid. Or it could be a combination of both these mechanisms – we’re still not sure. We did another experiment to test the second idea, but the results neither supported nor completely ruled it out (see the paper for more details!). We will try to get to the bottom of this in the future.

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Time for a cute male widow interlude! Look at him peeking out from behind that blade of grass.

For now though, let’s come back to the questions we set out to answer. Why do male black widows do web reduction? It allows them to monopolize the female, by making her web less attractive to other males. Courtship and mating last several hours, so if a male reduces the female’s web as soon as he arrives, he can decrease the likelihood of rival males arriving and interrupting. This may be very important at our field site, where competition for access to females appears to be fierce – during our second experiment, we had one intact web attract over 40 males in a single night! So web reduction is good for the male, because it helps him to avoid competition.

What about the female? Losing her web may be costly – she has to spend time and energy rebuilding it. However, we think she might actually benefit from web reduction too, and that the benefits may outweigh the costs. Sure, her web is important for prey capture and protection, but it’s also really attractive. So attractive, in fact, that even if she doesn’t add more pheromone, it will continue emitting its “come-hither” message for several days. Given number of males we saw arriving at each web during our experiment (40 in one night! even 10 is pretty extreme!), remaining attractive once she has already found a mate might not be so great. Having a choice between multiple males might be a good thing, but the female really only needs to mate once to fertilize all of her eggs. By “muting” her chemical signal though web reduction, the male might be doing her a favour: allowing her to rebuild her web without attractive pheromones (female sex pheromone production shuts off immediately after mating in black widows, but they don’t ever take down their existing webs). Rather than having to waste time and energy chasing off superfluous suitors, this may allow her to get on with the business of producing egg sacs!

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Female western black widow guarding her egg sac. These spiders are very protective mothers!

References and further reading (also linked in the text)

Baruffaldi, L., & Andrade, M. C. (2015). Contact pheromones mediate male preference in black widow spiders: avoidance of hungry sexual cannibals? Animal Behaviour, 102, 25-32.

MacLeod, E. C., & Andrade, M. C. (2014). Strong, convergent male mate choice along two preference axes in field populations of black widow spidersAnimal Behaviour, 89, 163-169.

Salomon, M., Vibert, S., & Bennett, R. G. (2010). Habitat use by western black widow spiders (Latrodectus hesperus) in coastal British Columbia: evidence of facultative group living. Canadian Journal of Zoology, 88(3), 334-346.

Stoltz, J. A., McNeil, J. N., & Andrade, M. C. (2007). Males assess chemical signals to discriminate just-mated females from virgins in redback spidersAnimal Behaviour, 74(6), 1669-1674.

Watson, P. J. (1986). Transmission of a female sex pheromone thwarted by males in the spider Linyphia litigiosa (Linyphiidae). Science, 233(4760), 219-221.