Rhomphaea: ridiculously long theridiids


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!


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.


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!


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!


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.


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



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]


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!).


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.


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.


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.

anal tubercle

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).


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.


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.


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!


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.


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.

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.


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.


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.


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


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.


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.


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.


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.  


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. 


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.


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.


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.


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.

Mimetidae_egg sac

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).


Photo: Catherine Aitken (used with permission).

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


Photo: Catherine Aitken (used with permission).

A great struggle ensues.


Photo: Catherine Aitken (used with permission).

The wasp emerges victorious, while the spider retreats.


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!

Crab with yellowjacket

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

Who eats spiders?

Spiders are awesome predators. Although there are a few exceptions, spiders are all professionals when it comes to eating other animals. But spiders have predators too! Who eats spiders? You might be surprised.

Birds are important predators of spiders, particularly in forest canopies.


A white-throated toucan eating a large spider in Guyana. Photo: Sean McCann.

Insectivorous birds such as great tits eat a variety of arthropods including insects and spiders. Early in their nesting season, spiders comprise up to 75% of the food great tit parents bring to their chicks!


Great tit (Parus major) carrying a false black widow spider – probably a meal for one of its offspring. Photo: Cliff, used with permission.

Spiders are also major predators of other spiders. Some wolf spider (family Lycosidae) species may even be some of their own most important predators. Wandering hunters like wolf spiders and jumping spiders tend to be opportunistic predators and will take most anything they come across, including other spiders.


Wolf spider (Lycosidae) eating a female pholcid that was carrying her egg sac – a nutritious bonus snack! Photo: Sean McCann


Another wolf spider (Lycosidae) eating a ground spider (Gnaphosidae). Photo: Sean McCann


A large female jumping spider (Phidippus) eating a much smaller zebra jumper (Salticus scenicus) Photo: Sean McCann

Some species even specialize on other spiders! Cellar spiders (Pholcus phalangiodes) not only capture insects and spiders using their own webs, but also enter the snares of other spiders and trick the owners into thinking they are prey by vibrating the silk lines. When the resident spider approaches what it thinks will be its next meal, it soon becomes dinner itself. The cellar spider’s incredibly long legs allow it to keep a safe distance while it subdues much larger spiders by wrapping them with silk.


Cellar spider (Pholcus phalangiodes) wrapping a much larger spider (possibly a lycosid) with silk in preparation for a very filling meal. Photo: Karla Thompson, used with permission.

Perhaps the most fearsome enemies of spiders are spider wasps in the family Pompilidae. Huge ‘tarantula hawks’ in the genus Pepsis (they can be up to 8 cm long with a 10 cm wingspan!) can take even very large tarantulas. First the wasp stings the spider, paralyzing it almost immediately. But things get much, much worse from there.


Tarantula hawk (Pepsis sp.) in French Guiana. This enormous wasp is 3 inches (8 cm) long! Photo: Sean McCann.

The wasp drags the paralyzed tarantula into a burrow, and lays a single egg on its abdomen. The spider remains paralyzed and trapped underground until eventually it meets its gruesome demise when the wasp larva emerges and begins to eat it alive.


A spider wasp dragging its victim (a paralyzed tarantula) into a burrow where it will become food for a baby wasp. Photo: David Crummey, licensed under CC BY 2.0


Poor spider! Photo: David Crummey, licensed under CC BY 2.0

So birds, spiders, and wasps are regular spider-eaters, but many others animals also partake now and then. Here are a few occasional predators of spiders: 

A toad’s diet may be up to 5% spiders.


Southern toad, Anaxyrus (Bufo) terrestris, eating a spider. Photo: Scott Beazley, licensed under CC BY 2.0

Lizards also eat spiders. In the Bahamas and the Caribbean, islands without anoles have 10 to 30 times as many spiders as islands without these lizards, suggesting that they can be rather important predators.


A lizard eating a spider. Photo: Jo Garbutt, licensed under CC BY 2.0.

Monkeys and humans also sometimes eat spiders! Fried tarantulas are a delicacy in some places in the world, including Cambodia. Although entomophagy (eating insects) is becoming popular as a more sustainable alternative to meat, I have to say that I’m not a big fan of the idea of eating tarantulas, which are slow-growing and long-lived creatures.


Fried tarantulas in Phnom Penh, Cambodia. Photo: Matthew Stevens, licensed under CC BY-NC-ND 2.0.

Finally, fish, bats and shrews also eat spiders occasionally. This certainly isn’t an exhaustive list, but I hope it gives you an idea of the range of animals that eat spiders. Stay tuned for future posts on some of the surprising things that spiders eat!


Edgar, W. D. (1969). Prey and predators of the wolf spider Lycosa lugubrisJournal of Zoology, 159(4), 405-411.

Foelix, R. (2010). Biology of spiders. Oxford University Press.

Gunnarsson, B. (2007). Bird predation on spiders: ecological mechanisms and evolutionary consequences. Journal of Arachnology, 35(3), 509-529.

Jackson, R. R., & Brassington, R. J. (1987). The biology of Pholcus phalangioides (Araneae, Pholcidae): predatory versatility, araneophagy and aggressive mimicry. Journal of Zoology, 211(2), 227-238.

Naef‐Daenzer, L., Naef‐Daenzer, B., & Nager, R. G. (2000). Prey selection and foraging performance of breeding Great Tits Parus major in relation to food availability. Journal of Avian Biology, 31(2), 206-214.

Nyffeler, M., & Knörnschild, M. (2013). Bat predation by spiders. PLOS ONE, 8(3), e58120.


Bolas spiders: masters of deception

Bolas spiders (members of the genus Mastophora, in North America) are famous for their unusual prey capture technique: rather than a web, they produce a single silk line with a super-sticky ball of glue at the end, which they fling at their prey.


Female Mastophora cornigera hunting with her ‘bolas’. (Photo: Matt Coors)

The common name ‘bolas spider’ is not particularly accurate, though. A real bolas – two or more weights connected by cord – is swung and thrown at an animal (like a horse, in the image below) in its entirety, and works by getting tangled around the legs of the target.


By John Miers [Public domain], via Wikimedia Commons

The spider’s ‘bolas’ differs in that it never leaves its owner’s grip, and works by getting stuck to the target, which is invariably a moth. Eberhard (1980) observed that a more appropriate name would be “sticky yo-yo spiders”. The sticky yo-yo prey capture technique is impressive enough (inspired by their speed and accuracy with the bolas, Eberhard named one species dizzydeani for Jerome “Dizzy” Dean, one of the greatest baseball pitchers of all time), but to fully appreciate the wonders of bolas spider biology, we must delve into the secret lives of these aromatic and cryptic spiders. They are masters of deception, both olfactory and visual.

Seductive scents

Hunting with a sticky yo-yo is all very fierce and exciting, but what are the chances that a moth is ever going to fly close enough for the spider to swing at? Not very high. Unless, like the bolas spider, you have a trick or two up your sleeve… er, leg… coverings. Adult female bolas spiders have the incredible ability to produce a chemical cocktail that make them smell just like female moths advertising for mates (actually, no one knows yet which part of the spider’s body is responsible for this wonderful trick). Innocent male moths following what they perceive to be a pheromone trail (whose chemical message indicates that it leads to a sexually receptive female moth) are thus duped into coming in close enough for the spider to strike. This is called “aggressive chemical mimicry”, and it is awesome.

Moth sex pheromones are typically blends of two or more chemical compounds in very specific ratios. The particular chemicals and ratios allow male moths to discriminate between females of their own and other species. If a bolas spider produced just one moth pheromone, they probably wouldn’t do very well, because their diet would be restricted to only a single moth species. It turns out that each species of bolas spider attracts several kinds of male moths, and the best studied of these is Mastophora hutchinsoni.


Bristly cutworm moth, Lacinopolia renigera. (Photo: Andy Reago & Chrissy McClarren; licensed under CC BY 2.0)

Smoky_tetanolita_kestrel338_CC BY-NC-ND 2.0

Smoky tetanolita, Tetanotolita mynesalis. (Photo: kestrel 360; licensed under CC BY-NC-ND 2.0)

Mastophora hutchinsoni attracts four kinds of moths, but more than 90% of their prey consists of two species in the family Noctuidae: the smoky tetanolita (Tetanolita mynesalis) and the bristly cutworm (Lacinopolia renigera). These two moth species produce entirely different sex pheromones, and they are active at different times of night. The problem for the bolas spider is that the bristly cutworm pheromone interferes with the attractiveness of the smoky tetanolita’s pheromone.


Here’s where the bolas spiders start to get really fancy. Let’s join an M. hutchinsoni female for a night of hunting, and learn some of her secrets.


M. cornigera female preparing for a night of moth hunting. (Photo: Matt Coors)

She begins by building her horizontal “trapeze” line, from which she then hangs motionless, with front legs extended in hunting position (but with no bolas, yet). She is already emitting the sex pheromones (well, analogs that are close enough!) of both prey species, but so far, only the early-flying bristly cutworm is active. They aren’t put off by the smell of smoky tetanolita females mixed in with the pheromone of a female of their own species, and soon one is winging its way toward the seductive scent coming from the female spider. It passes close by, but out of reach. This moth is lucky, for now. But no matter; his fate is not our immediate concern. The spider’s outstretched legs are covered with tiny vibration-sensitive hairs (called trichobothria) that allow her to detect the sound of the moth’s wing beats nearby. Now that she knows there is prey about, she springs into action and spends the next minute or two building her sticky bolas.


Female M. cornigera hunting with her bolas. (Photo: Matt Coors)


Once her weapon is complete, she returns to her prey-capture position, with the bolas hanging from one of her outstretched front legs. For her next trick, she will again rely on her ability to detect the wingbeats of flying moths with her leg hairs. She waits patiently, silent and still.




Soon, another hapless male moth picks up the scent and starts winging towards the bolas spider. When her sensory hairs tell her the time is just right, she takes a swing at the approaching moth and connects. Although the moth struggles, shedding scales in its effort to escape, the wet stickiness of the bolas holds it fast. The spider reels the moth in and delivers a fatal venomous bite. She waits a few moments, then wraps her prize in swathes of silk and hangs it carefully from her trapeze line to eat later. The night is young, and the moths will continue flying for some hours yet. The bristly cutworms will remain active until 22:30. Our spider builds a fresh bolas, and settles in to wait. Gradually, the smell of bristly cutworm sex pheromone coming from the spider fades. The smell never disappears entirely, but is soon faint in comparison to the scent of a female smoky tetanolita. The smoky tetanolita males will come out after 23:00, and our spider will be ready for more deadly deception.


Female M. phrysonoma with captured moths. (Photo: Keith Simmons; licensed under CC BY-NC-SA 2.0)

So far, we’ve discovered some of the adult female bolas spider’s secrets to success, but what about juveniles and males? They don’t use a bolas, but they are no less stealthy and deceitful than their counterparts. Young bolas spiders are also employ aggressive chemical mimicry to attract prey, but they specialize on male moth flies in the family Psychodidae. Each bolas spider species is especially attractive to a particular species of moth flies. It appears to be a pleasing coincidence that small bolas spiders prey on moth flies until they graduate to real moths. Whether or not the sex pheromones of the psychodids captured by each spider are similar to those of moths they specialize on is currently a mystery.

a moth fly

Moth fly (Psychodidae). (Photo: Ted C. MacRae)

Optical illusions

Mastophora females are not only masters of chemical deception, but they are also visually cryptic, and hide in plain sight from their own potential predators. They do this by mimicking bird poop.


Excellent bird-poop mimicry by Mastophora cornigera. (Photo: Matt Coors)

The female spiders spins herself a silken mat on the surface of a leaf, and clings to it with her legs drawn in tightly around her cephalothorax.


Another bird poop mimic, female M. phrysonoma, with visitors! (Photo: Matt Coors)

But wait, what are those tiny red things? At first glance, they could easily be mistaken for mites, but no! These are tiny males, presumably interested in mating with the comparatively massive female. Bolas spider males are usually less than 2 mm long, while females are typically 10 – 15 mm long, and sometimes as large as 2 cm!


Another shot of the incredible bird poop mimicry and extreme sexual dimorphism of M. phrysonoma. (Photo: Matt Coors)

Because the females are so cryptic and males are so tiny, almost nothing is known about the sexual behaviour of bolas spiders. As a researcher studying sexual communication and mating behaviour in spiders, I sure would love to know how the males in the photos above found the female and what happened next! Most likely, the female bolas spiders produce attractive sex pheromones just like the moths whose chemical communication they exploit. As far as I am aware, however, no one has investigated the sex pheromones of bolas spiders. One hypothesis that might explain the evolution of their mimicry of moth pheromones is that their own chemical signals have compounds in common with those of their prey. In fact, this is a hypothesis that Andy Warren is investigating for a different group of spiders that also mimic moth pheromones – orb weavers in the genus Argiope.

If you’re not familiar with spider systematics, it might seem odd that two groups of spiders that look so different and have such different prey-capture techniques share the amazing ability to lure male moths to their doom. In fact, bolas spiders are orb-weavers (at least, they are members of the orb-weaver family Araneidae), they just don’t build webs like most of their relatives. Like orb-weavers, bolas spiders regularly eat their silken traps and recycle the silk proteins to use another day.

Argiope_aurantia_Suzanne_Cadwell_CC BY-NC 2.0

Argiope aurantia female on her orb-web. (Photo: Suzanne Cadwell; licenced under CC BY-NC 2.0)

See the family resemblance?

To see a female bolas spider in action, check out this video clip from David Attenborough’s “Life in the Undergrowth” series. (The bolas spider segment starts at 3:00, but the first few minutes about the redback spider are also worth a watch!)


Special thanks to Matt Coors for kindly letting me feature his fantastic photographs in this post!


Eberhard, W. G. (1980). The natural history and behavior of the bolas spider Mastophora dizzydeani sp. n. (Araneidae). Psyche: A Journal of Entomology87(3-4), 143-169. http://dx.doi.org/10.1155/1980/81062

Haynes, K. F., Yeargan, K. V., & Gemeno, C. (2001). Detection of prey by a spider that aggressively mimics pheromone blends. Journal of insect behavior,14(4), 535-544. http://link.springer.com/article/10.1023/A:1011128223782

Haynes, K. F., Gemeno, C., Yeargan, K. V., Millar, J. G., & Johnson, K. M. (2002). Aggressive chemical mimicry of moth pheromones by a bolas spider: how does this specialist predator attract more than one species of prey? Chemoecology, 12(2), 99-105. http://link.springer.com/article/10.1007%2Fs00049-002-8332-2?LI=true

Yeargan, K. V. (1988). Ecology of a bolas spider, Mastophora hutchinsoni: phenology, hunting tactics, and evidence for aggressive chemical mimicry. Oecologia, 74(4), 524-530. http://www.jstor.org/stable/4218505

Yeargan, K. V. (1994). Biology of bolas spiders. Annual review of entomology39 (1), 81-99. DOI: 10.1146/annurev.en.39.010194.000501 

Yeargan, K. V., & Quate, L. W. (1996). Juvenile bolas spiders attract psychodid flies. Oecologia, 106(2), 266-271. http://link.springer.com/article/10.1007/BF00328607

Yeargan, K. V., & Quate, L. W. (1997). Adult male bolas spiders retain juvenile hunting tactics. Oecologia, 112(4), 572-576. http://link.springer.com/article/10.1007/s004420050347