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.

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.

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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.

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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.

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

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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.

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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.

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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.

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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.

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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.

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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.

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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!

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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.

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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!

References:

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

 

 

Spiders of Lost Lagoon

This weekend, I was lucky to spend a rare rain-free November morning in Vancouver’s famous Stanley Park with Sean McCann, who kindly provided all the photos for this post. Despite the late season and cool weather, it turned out to be a very spidrous (a term coined by Sean) day indeed! We must remember that the end of Arachtober does not necessarily mean the end of spider season, as Eric Eaton pointed out in a recent Spider Sunday post.

Our first spider-observation stop was outside the Lost Lagoon Nature House. What at first glance looked like a dirty and unremarkable garage door turned out, upon closer inspection, to be a veritable spider heaven!

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Here I am making notes on an impressive aggregation of spiders.

Although not quite on the massive scale of the aggregation of thousands of orbweavers inside a wastewater treatment plant that Gwen Pearson wrote about recently, I estimate that the area around this single garage door is home to several hundred spiders all living in extremely close proximity. In this case, the aggregated webs are just a couple metres away from the edge of Lost Lagoon, a freshwater habitat that produces large numbers of chironomid midges as well as larger aquatic insects. Lights attract these insects, making this the perfect hunting ground at night, when the spiders are most active.

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It’s hard to see individual spiders at this scale, but looking closer, they are everywhere!

Here’s a closer look  at one small area of the door (zooming in on the upper right corner of the photo above). Two large females rest in the open while a third hides away in a silken retreat next to a cluster of 3 egg sacs.

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Almost all the spiders in this aggregation were members of a single species, the bridge orbweaver Larinioides sclopetarius (family Araneidae). Here are some closer shots of a male and female:

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Male Lariniodes sclopetarius against the blue backdrop of the building.

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Female Lariniodes sclopetarius posing on some nearby vegetation.

We did find a few spiders other than bridge orbweavers on the building. A female L. sclopetarius and what’s most likely a juvenile Eratigena (formerly Tegenaria) appeared to be sharing the same retreat in a cement pillar.

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Moments before this photo was taken, these two were hunkered down close together in the pit in the cement, apparently  oblivious to one another.

Right on the other side of the same pillar, this male longjawed orbweaver Tetragnatha elongata was hanging out.

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It turns out that Lariniodes and Tetrgnatha are the usual suspects when it comes to communal living and megawebs. Spiders in both genera like to live near water as was the case here next to the lagoon. Lariniodes sclopetarius often build their webs on human-made structures, and especially prefer to be next to lights (Greene et al. 2010 and references therein). This preference was very evident at the Nature House – of the four identical  garage door sections of the side of the building facing the lagoon, the spiders were almost exclusively living on the only one with a light.

Although our first stop provided plenty of arachnological excitement for one day, we eventually moved on and explored the rest of the lagoon.

We found this male Pimoa altioculata and several others of the same species on webbing underneath the railing of a small footbridge.

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Spiders in the family Pimoidae are related to the linyphiids, and also build sheet-webs.

When Sean removed the spider from his web to try to get some better shots, he immediately went into “play dead” mode, tucking all his legs up tightly around his body for defense.

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Several more longjawed orbweavers were hanging out under the railings of the same bridge.

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Another Tetragnatha sp. These spiders are typically found near water.

We also found this beautiful example of a hammock-shaped sheet web built by a small linyphiid.

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In this shot you can see the silhouette of the spider at the upper left hand side of the “hammock.”

We admired the web for some minutes before noticing the resident spider, who eventually came out onto the web for the lovely shot below:

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You can tell from the bulbous pedipalps that this is a subadult male. I am pretty sure the species is Neriene digna.

All in all it was a wonderful day at the park. I hope your November is just as spidrous as ours has been so far here on the wet coast!

Reference:

Greene, A., Coddington, J. A., Breisch, N. L., De Roche, D. M., & Pagac, B. B. (2010). An Immense Concentration of Orb-Weaving Spiders With Communal Webbing in a Man-Made Structural Habitat (Arachnida: Araneae: Tetragnathidae, Araneidae). American Entomologist, 56(3), 146-156.

Hola from Honduras!

We finally made it to our destination, the town of Gualaco in the department of Olancho, after three long days of travel (including an unexpected detour through San Pedro Sula due to poor weather preventing our plane from landing in Tegucigalpa). After spending two nights in a local hotel, we’re now installed in an affordable apartment (the rent is about a tenth of the cost of similar accomodation back home in Vancouver) that will serve as our home base for the coming months.

Things are definitely different here – for one thing, there is no hot running water in Gualaco.  This is the slightly scary, and mostly ineffective, electric showerhead that was in our hotel room. We are not sure yet whether we’ll invest in one for our new home.

Yesterday, we took a trip up some very interesting roads to the pine forest where we’ll start our caracara work. We visited the site where a local named Isidro (who will be our guide for the next month) monitored a red-throated caracara nest last year.

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We had a very long and interesting ride, with eight people in one 4-wheel drive pickup, along some extremely bumpy and muddy roads. We passed this unfortunate boa constrictor, which evidently chose the wrong time to cross the road.

Although we didn’t have much time to stop and investigate or photograph cool animals as we hiked in and out from the nest site, Sean did manage to snap a couple of shots of spiders that we passed by.

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A wolf spider (family Lycosidae) with her silk-wrapped egg sac attached to her spinnerets.

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An Argiope (Araneidae) with a beautiful star-shaped stabilimentum.

We also have plenty of familiar spider friends in our apartment, that appear to be helping with the moth infestation.

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Lucky for us, our apartment contains an abundance of cellar spiders (Pholcidae)! Here’s a female with her egg sac clasped in her chelicerae, and an attending male.

Once we’ve had more time to explore local habitats, I am sure I will be able to post lots more about the spiders of Honduras! Hasta luego!

Thanks to Sean for all the photos.