A cunning crab spider

Posted on April 24, 2015 by cataranea

Sean McCann recently returned from an epic journey through the rainforest of Guyana in search of caracaras, and is busy blogging about his adventures over at Ibycter.com (so you should check it out!). To make up for not taking me along, he found and photographed lots of awesome spiders for me to blog about. Here’s the first one!

Here we have a male crab spider (family Thomisidae) with its prey: an ant in the genus Dolichoderus*. At first glance, this may not seem particularly exciting. A small, hairy, black spider eats an insect. What’s so special about this scene?

Well, the spider appears to be Strophius nigricans, reported to be a specialist predator of ants. Most animals are not big on eating ants because they are generally distateful and well-defended by strong mandibles, stings, and defensive compounds. So specializing on ants is not particularly common, and tends to come along with some neat adaptations.

Strophius nigricans is not well studied, but I managed to find one paper about its predation behaviour. Oliveira and Sazima (1985) observed a male S. nigricans carrying an dead worker ant (Camponotus crassus) in the field in Brazil, and took it back to the laboratory to make some observations. The spider never let go of his ant carcass – this would come in handy later. In captivity, he was provided with some more C. crassus workers, and here his secrets were revealed.

The Strophius male used his ant corpse as a shield for protection against ants during predation. To eat ants, one must spend time near ants, but they don’t take kindly to intruders. The dead-ant-shield provides a clever disguise. Most ants don’t have especially good vision, and instead rely mainly on their senses of touch and smell. Whenever the Strophius male was approached by an ant, he would present his previous meal, which (obviously) feels just like another ant, and, if recently deceased, probably smells right too. As the spider pursued his prey, always attempting to sneak up from behind, he held the ant corpse aloft. Once within striking distance of an unsuspecting ant, he quickly dropped the shield and bit his new victim. Once dead, this new ant was used as a shield.

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Unlike a related crab spider species that preys on ants, Aphantochilus rogersi (a remarkable ant-mimic), Strophius doesn’t look all that much like its victims. A. rogersi specializes on Cephalotes ants, which have relatively good vision, but its excellent mimicry is probably more important as a defense against visually hunting predators that avoid eating ants. However, a similar mode of defense is not necessarily out of the question for Strophius. The ants it preys on are black and have white hairs on the abdomen. From above, the spider carrying its ant-shield might look just enough like an ant carrying its comrade to fool a potential predator such as a bird.

As it turns out, the conclusion that Strophius nigricans are specialists on the ant species Camponotus crassus appears to be based on Oliveira and Sazima’s observations of the single male discussed above. Here we’ve seen that the spider also takes another species, and it seems that its prey capture technique should work just fine as long as the shield matches the subsequent target prey species. The visual mimicry would presumably be just as effective for any similar sized black ants. This certainly seems like a cool system that could use more investigation!

*Thanks Alex Wild for the ID!

References:

Oliveira, P. S., & Sazima, I. (1984). The adaptive bases of ant‐mimicry in a neotropical aphantochilid spider (Araneae: Aphantochilidae). Biological Journal of the Linnean Society, 22(2), 145-155. (pdf)

Oliveira, P. S., & Sazima, I. (1985). Ant-hunting behaviour in spiders with emphasis on Strophius nigricans (Thomisidae). Bulletin of the British Arachnological Society.

Ghost spiders (Anyphaenidae)

Posted on April 6, 2015 by cataranea

Recently, Sean found a lovely pale spider in his mother’s garden in Victoria. Neither of us recognized it, and after a bit of research, I was able to identify it as a member of the family Anyphaenidae. Spiders in this family are called ghost spiders, and this is the first one I have ever encountered. She is now living in a petri dish on our bookshelf, and has made herself a cozy silk retreat inside a curled leaf.

Anyphaena aperta female (missing her left front leg) photo: Sean McCann

Not much is known about the natural history of these secretive spiders. Apparently they are generally nocturnal hunters that spend their days in their silken retreats. Apart from building these “sleep sacs” under leaves or rocks (and of course spinning egg sacs), ghost spiders don’t have much use for silk.

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Anyphaena accentuata in her silken retreat under a leaf. Photo: Ferran Turmo Gort (licensed under CC BY-NC-SA 2.0)

Ghost spider body forms and lifestyles are similar to those of the sac spiders (family Clubionidae), and in fact they used to be considered clubionids. They also have some similarities to ground spiders in the family Gnaphosidae. Members of all three families are wanderers with prominent spinnerets. Luckily for me and others without regular access to a microscope, there are some fairly obvious characteristics that help distinguish Anyphaenidae from other spider families.

Less reliable, but easier to see, is the eye arrangement.

Ground spiders in the family Gnaphosidae often have some oval eyes, whereas anyphaenids’ eyes are all round.

A ground spider in the genus Zelotes (Gnaphsosidae) with her lovely pink egg sac. Note the barrel-shaped spinnerets. I know you can’t really see her eyes – click the link above for a drawing. Photo: Sean McCann

And unlike many sac spiders in the family Clubionidae, the anterior median eyes (AME; the central pair closest to the front of the head) are usually smaller than the other eyes.

Sac spider with relatively large anterior median eyes. Photo: Sean McCann

Anyphaena eye arrangement. The anterior median eyes (central pair in the front row) are smallest. Photo: Dann Thombs (licensed under CC BY-ND-NC 1.0)

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Dorsal view of eye arrangement of an Anyphaena male. Photo: Kyron Basu (licensed under CC BY-ND-NC 1.0)

The real giveaway characteristic of anyphaenids, however, is the tracheal spiracle (one of the openings of the respiratory system in spiders). To get a good look at this, it’s useful to have a Spi-Pot. In other similar-looking spiders the tracheal opening is located close to the spinnerets. In ghost spiders, it is closer to the centre of the abdomen.

Anyphaena_aperta_male_KenSchneider_bugguideCCBY

Ventral view of a male Anyphaena aperta. Photo: Ken Schnieder (licensed under CC BY-ND-NC 1.0)

The horizontal groove on the underside of this spider’s abdomen (across the darker patch in the middle) is the tracheal spiracle.

Although not much to look at from the outside, the tracheal system of the anyphaenids may provide us with some clues about their natural history. Internally, the tracheae of ghost spiders are much wider than those of sac spiders. This may be because they have a more active lifestyle than sac spiders; they are certainly very fast runners. Males have even larger tracheae than females, which Platnick (1974) concluded is likely related to their extremely vigorous courtship displays. During courtship, Anyphaena accentuata males vibrate their abdomens up and down so quickly that it becomes a blur. In contrast, sac spider courtship has been described as “sluggish”.

The ghost spiders could certainly use more study, and I’ll be keeping an eye out for them from now on!

Anyphaena aperta again. 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). link

Platnick, N. (1974). The spider family Anyphaenidae in America north of Mexico. Bull Mus Comp Zool Harvard Univ. 146: 205-266. link

Bolas spiders: masters of deception

Posted on March 17, 2015 by cataranea

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.

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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.

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.

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.

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.

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 Entomology, 87(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 entomology, 39 (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

Inspidered arts and crafts

Posted on January 29, 2015 by cataranea

Now that I am finished with my MSc (yay!) I have great plans for dedicating more time to blogging. Please stay tuned for new posts about spider biology and natural history soon! For now, allow me to ease back into the blogging swing of things with this post celebrating spiders in art.

Do you love spiders? Are you into fibre art, digital art, or pen/paint/crayon-on-paper art? Then this post is for you! Here are some creative arts and crafts projects that are sure to inspider.

Watercolours

Black widow in watercolour pencils by Chris Buddle

I received this beautiful black widow artwork by Chris Buddle in the mail just the other day. Spiders are of course perfect subjects for drawing and painting. Not confident in your artistic abilities? Why not start with this simple spider web project using crayons and watercolours? This would be a very fun activity to do with young arachnophiles. I especially love this tangled web made by the blog author’s daughter.

Spider word art

Black widow and fly word art. Original photo by Sean McCann, word art created by Mike Boers. Text from my thesis!

For Christmas, I was the lucky recipient of framed prints of this brilliant artwork. Mike Boers used his coding expertise to generate creative word art from Sean McCann‘s photographs and text about the subjects of the photos.

Jumping spider word art. Original photo by Sean McCann, word art by Mike Boers. I am not sure where the text for this one came from, but it is all about jumping spiders!

A digital image consists of an array of pixels that can be represented by a matrix of numbers for each colour channel. The value of each entry in these matrices represents the intensity of the colour of that particular pixel. Mike replaced each of the pixels in three colour channels (magenta, cyan, and yellow) with a letter from a chunk of text. In the first image above, he used the three chapters of my thesis about black widows! If you click on one of the images above to enlarge it, and concentrate really hard on reading only the pink letters, for example, you might be able to make out some of the text. The size of each letter corresponds to the colour intensity value of the corresponding pixel.

Knitted accessories

Socks knitted by Samantha Vibert (photo: Sean McCann)

My friend and fellow arachnologist Samantha Vibert knitted these fabulous socks for me last year. Here is a free pattern that is very similar. The spider chart could be used on any knitted object, not just socks. I’ve recently seen spiders in some high-fashion items like this sweater from Hermès, which unfortunately has the silk coming out the wrong end of the spider and costs more than the 10-day spider identification course being offered by the American Museum of Natural History in Arizona this summer (I’ll let you guess which one I plan to invest in). Luckily, if you can knit, you can create beautiful, affordable, and anatomically correct spider-embellished garments and accessories that far outshine any commercially available product!

Jumping spider fingerless mitts made by me (photo: Raphaël Dury)

Speaking of spidery hand-knits, I recently made these fingerless mitts for entomologist and salticid enthusiast Guillaume Dury. I used this free pattern for the mitts, and modified this pattern to make the jumping spider design.

If you’ve made any spider art recently, or use any of these ideas to make something in the future, I’d love to see them! Feel free to post in the comments, or tweet to @Cataranea on twitter.

Spiders of Lost Lagoon

Posted on November 10, 2014 by cataranea

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!

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.

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.

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:

Male Lariniodes sclopetarius against the blue backdrop of the building.

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.

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.

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.

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.

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

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.

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:

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.

The truth about spider bites: “Aggressive” spiders and the threat to public health

Posted on September 25, 2014 by cataranea

This post was written with Chris Buddle, and originally appeared on his blog Expiscor at Scilogs.com

Misinformation about spider bites is everywhere

Spiders are polarizing: people tend to be fascinated or fearful, and for some, Arachnophobia can be quite serious. However, spiders are often feared unnecessarily. They are quickly blamed for almost ALL unexplained bites or lesions!

It doesn’t help that there is an incredible amount of misinformation and fear-mongering related to spiders in the popular media and all over the internet. What’s worse, misinformation about spiders also appears in the medical literature. For example, the journal Emergency Medicine recently published an article on bites and stings that made the following claims:

“The [hobo spider] is considered aggressive and tends to bite even with only mild provocation. The clinical presentation, inclusive of systemic reactions, is similar to that of the brown recluse spider.”

This got us all riled up, and we decided to set the facts straight:

1. The hobo spider is not aggressive.

Here I am, holding an “aggressive” hobo spider. Photo S. McCann.

Exhibit A (photo, right): the allegedly aggressive hobo spider. This female hobo was minding her own business on her webuntil being rudely removed to a human hand and made to pose for photographs.

As for its supposed tendency to bite when provoked, Samantha Vibert, an arachnologist at Simon Fraser University says,

“During my PhD, I’ve studied the ecology and courtship behaviour of the hobo spider, Eratigena agrestis. This work entailed surveying dense populations of the hobo spider in the field and conducting experiments in the lab. Over the course of several years, I’ve handled hundreds of hobo spiders. I am always puzzled when I hear the hobo spider described as an “aggressive” species. Their one and only strategy when disturbed is to run away. The only mildly disturbing thing about them is the speed with which they bolt! When they feel threatened, they’ll abandon their web and make a dash for the nearest dark corner. I can only assume that their bad reputation stems from 1) a misunderstanding of their scientific name (agrestis means “of the field”, and not “aggressive”) and 2) their appearance. For people who dislike spiders, their relatively large size and long legs are not endearing. In fact, this spider is very meek and gentle but sadly misunderstood!”

2. The evidence that hobo spiders cause dermonecrotic lesions is poor and largely circumstantial.

Hobo spiders are European, but they were introduced to North America in the early 20^th century and have since become established in the northwestern US and British Columbia, Canada. Hobo spiders live peacefully alongside humans in Europe, where nobody seems to be all that concerned about them. A 2001 study found no support for the hypothesis that the venom of North American hobo spiders differed from that of their European counterparts in its ability to cause necrosis. Most of the evidence tying hobo spiders to dermonecrotic lesions in medical case studies is weak and circumstantial. For example, the mere presence of this species in the house or even the neighbourhood where the supposed bite victim lived has been used to implicate hobo spiders. There only seems to be one case reported in the medical literature with reasonably incriminating evidence – the dead spider was found crushed under a pant cuff. But even in this case, the person had a pre-existing medical condition and did not seek medical attention for more than 2 months after the bite, casting doubt on whether the spider’s venom was actually responsible for necrosis.

A female hobo spider. Photo by S. McCann.

3. Spider bites are extremely rare, and often misdiagnosed.

It is disappointing to see these myths about spiders propagated among some doctors and the public, but more importantly, it is dangerous. Here is a list of some of the actual conditions that have been misdiagnosed as resulting from spider bites:

infections (bacterial, viral, and fungal)
cancers (basal cell carcinoma and lymphoma)
poison oak and ivy
burns
Lyme disease (resulting from tick bites)
vascular disorders
pyoderma gangrenosum

Arachnologists Robb Bennett and Rick Vetter advise doctors that,

“The criterion standard for spider-bite diagnosis should be a spider caught in the act of biting or otherwise reliably associated with a lesion (and properly identified by a qualified arachnologist). Unless this standard is met, a working diagnosis of a spider bite should not be considered. Any of the above conditions are more likely.”

In spite of there being no brown recluses in Canada, it is common to hear about people who have been diagnosed with brown recluse bites here. Most of these folks never saw a spider or felt a bite, but had their mysterious lesion diagnosed as a spider bite by their doctor, who they trust as an expert. This comic nicely sums up why the vast majority of the time, it is safe to assume that a spider did not bite you.

The poor brown recluse is always getting blamed for unexplained lesions. Photo by M. Bertone, reproduced here with permission.

Even where there are brown recluse spiders, they hardly ever bite people. There was a family home in Kansas that had 2,055 brown recluse spiders collected from it over a 6-month period, and no one living in the house got bitten. Still not convinced? In Florida, medical professionals diagnosed 124 brown recluse bites over 6 years. That’s 124 people who accidentally got near enough to the alleged spiders to be bitten, while going about their everyday business (only one of them ever produced an actual brown recluse for identification). Arachnologists – we’re talking people who actively go around seeking outspiders in likely spots – found only 5 brown recluses in Florida over the same 6-year period and a total of only 70 brown recluse spiders over 100 years. The numbers simply do not add up.

Did we mention that spiders hardly ever bite people?

Sometimes spiders do bite people, and a few species are legitimately considered medically significant. In North America, black widows as well as brown recluse bites are serious and certainly may require medical attention. However, black widows in particular have an undeserved bad reputation. They are not aggressive, rarely bite, and even when they do, they often don’t inject any venom. Most news articles about black widows refer to them at least once as deadly – often in the headline. According to the American Association of Poison Control Centers, 2,246 black widow bites occurred in all of the United Stated in 2012 (that doesn’t mean they were verified as actual black widow bites, just that they got reported, so this is almost certainly an overestimate). Only 21 of these reported bites resulted in major, but non-lifethreatening, symptoms, and no one died. Compare those zero deaths with the 36,166 traffic fatalities in the US in 2012. Cars are not regularly described as deadly but perhaps they should be. It would be more reasonable to fear automobiles than black widows. Arachnophobia is of course a legitimate condition, but there really are a lot of worse things to worry about.

A black widow, photographed by S. McCann.

4. There are serious consequences of spider bite misinformation and misdiagnosis

Assuming every unknown lesion is a spider bite can prevent accurate diagnosis, and delay proper treatment. Inappropriate treatment based on the misdiagnosis may be ineffective or worse, harmful. Overzealous diagnoses of spider bites can also lead to arachnophobia and reckless, unwarranted attempts to rid homes of spiders. Unnecessary exposure to pesticides is probably much riskier than sharing your home with spiders.

In sum, we hope this post is seen as a “Public Service Announcement” (or better yet, a “Public Spider Announcement”) and that we can help dispel some myths about spiders. We should be celebrating their incredible biology and natural history, and we should look to spiders as our allies in controlling pest insects, or taking down mosquitoes.

We should look at spiders in awe, rather than in fear.

Spiders Unraveled! Outreach at Iona Beach

Posted on September 15, 2014 by cataranea

This weekend was, to my knowledge, the first ever spider day hosted by Metro Vancouver Regional Parks. Along with a fantastic crew of volunteer spider enthusiasts and park staff, I had the great pleasure of sharing some of the incredible biology of spiders and the joys of being a naturalist with kids and adults alike.

Here are some of the highlights of the day in photographs, kindly provided by Mike Boers and Sean McCann.

Gwylim Blackburn greeted visitors at the become a naturalist station. Here kids could make or borrow all the supplies they might need to be arachnologists for the day! These included ‘pooters’ (aspirators) made out of straws for collecting small spiders, personalized field notebooks, pencils, magnifying glasses, collecting containers, and a customized field guide to the spiders of Iona Beach.

Gwylim with his table of supplies for creating the tools to become a naturalist! photo: Sean McCann

Building pooters and field notebooks. Photo: Sean McCann

A triumphant young naturalist holds her field notebook aloft, prepared for the adventures ahead! Photo: Sean McCann

Tanya Stemberger served up cricket smoothies and crunchy beetle larvae at the eat like a spider station. Here visitors learned about the health and environmental benefits of eating insects like spiders do! Read more about this part of the event here.

Tanya serves up a cricket smoothie for some kids who are brave enough to try entomophagy! Photo: Mike Boers

Some were a bit sceptical about the idea of eating insects at first.

Photo: Sean McCann

But most were enthusiastic!

Adding the cricket protein powder to the smoothie. Photo: Sean McCann

In the end, almost everyone accepted the challenge and won a special entomophagy achievement award for their bravery!

Tanya shows off the highly prized entomophagy award certificate. Photo: Sean McCann

Next, kids got to participate in the spider olympics! The first event was to avoid predation by a spider. The challenge was to to climb through a web without creating vibrations that would ring the dinner bells and alert the resident spider to the presence of potential prey!

The spider web challenge! Photo: Sean McCann

Other spider olympic events included trying to jump as far as a jumping spider (they can jump distances up to 25 times their body length!) and run as fast as a house spider (330 body lengths in 10 seconds!).

The highlight of the day for most visitors was the spider tour of the beach with Sean McCann, where kids got to learn how to find spiders and put their new field notebooks and pooters to use!

Every hour Sean set out with a new group of naturalists to find the hidden treasures of Iona Beach. Photo: Mike Boers

Sean took his crew of naturalists to several habitats in search of spiders, starting with his favourite: under the driftwood.

Sean demonstrates his log-flipping technique. Photo: Mike Boers

Collecting a specimen! Photo: Mike Boers

There are all kinds of wonders to be found under the logs if you look closely! Photo: Mike Boers

The tour then moved on to using beating sheets to collect spiders from vegetation, and also included sampling the rich spider fauna on the walls of the washroom building.

Samantha Vibert and I introduced interested arachnophiles (and a lot of unsuspecting cyclists stopping for water/washroom breaks!) to basic spider anatomy and diversity. We had live specimens of several local species representing both wandering hunters and web-builders.

Basic spider anatomy poster featuring a hobo spider, one of the commonest spiders found under the logs at Iona Beach. Created by Sean McCann

I greet my first visitor of the day, with much excitement and waving of hands. Photo: Sean McCann

Sam and one of our most enthusiastic young arachnologists, who stayed most of the day and went on 3 of the 4 spider walks! Photo: Sean McCann

All in all, I think the day was a great success! We had over 120 visitors, and a ton of fun. I hope it happens again next year!

A wolf spider, Arctosa perita, on the sand of Iona Beach. Photo: Sean McCann

Here’s a small sample of the diverse spiders that we found on the day, or brought from nearby sites (photos by Sean McCann).

: Castianeira longipalpa, an inhabitant of Iona Beach

: These small spiders are generalized ant-mimics

: A long jawed orbweaver collected from the vegetation

: A giant house spider. Along with hobo spiders, this is one of the commonest species under the logs at Iona.

: False black widow, collected from the washroom

: A male orb weaver

: A ground spider in the family Gnaphosidae

: Gnaphosids have distinctive cylindrical spinnerets

: Male western black widow, from Centennial Beach. Black widows do not live at Iona, even though it seems like their kind of habitat.

: Phidippus johnsoni, our largest jumping spider, commonly found at Iona

: Female Habronattus americanus, another jumper that is abundant at Iona

A comb-tailed spider

Posted on August 4, 2014 by cataranea

Last weekend, I joined a group of fellow arachnophiles for a day at Burns Bog. We did not achieve our goal of finding the rare ground spider Gnaphosa snohomish (a bog specialist), but instead we met a very common spider that is nonetheless not well known: a comb-tailed spider in the family Hahniidae.

Neoantistea magna, a common yet mysterious forest-dweller (photo Sean McCann).

A distinguishing feature of spiders in the subfamily Haniinae is the arrangement of the spinnerets in a single row like the teeth of a comb – thus the common name.

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The arrangement of the spinnerets of ‘comb-tailed’ spiders in the subfamily Hahniinae. (Photo by Tom Murray, licensed under CC BY-ND-NC 1.0)

I generally think of spiders as being one of two basic types: wanderers or web builders. The wanderers include visually hunting ground dwellers like wolf spiders, whereas web building spiders are sit-and-wait predators that rarely leave their silken snares. This is overly simplistic, of course, but asking “web or not?” is often a useful first step in classifying spiders. The genus Neoantistea, however, gave me a first encounter with members of an intermediate group known as vagrant web builders.

The sheet webs of Neoantistea spiders are tiny – typically less than 5 cm across. They are built in moss or across shallow depressions such as those formed by the tracks left by animals walking on soft ground. The diminutive spiders (their total body length is less than 5 mm) live under their webs, retreating into crevices in the litter or moss when disturbed.

Small sheet-web of Neoantistea magna (photo Sean McCann).

What makes these spiders unusual for web builders is that although the web can be a useful aid for catching prey, it is not necessary. Neoantistea magna have reasonably large eyes and can recognize and hunt prey just as easily off of their webs as on them (Engers & Bultman 2006).

A portrait of a male Neoantistea magna, showing the arrangement of the relatively large eyes (photo Sean McCann).

Although it was easy to identify the spiders we found to genus – the distinctive spinnerets leave no doubt as to the family, and of the North American members of the Hahniinae, Neoantistea is the only genus of web builders – determining the species was another matter entirely. Usually spider identification relies on close examination of the genitalia.

To ID this handsome fellow, two of the key features were the tibial apophysis and the patellar spur, tiny protrusions of the pedipalps which are very difficult to see without a microscope (here’s a diagram of the segments of the pedipalps).

The key to identifying spiders often lies in the features of their elaborate genitalia. Here the large curved outgrowth on the tibia and the hooked spur on the patella of the pedipalp are circled (photo Sean McCann).

Speaking of genitalia, although very little is known about the biology of Neoantistea magna, there is one report of mating behaviour (Gardner & Bultman 2006). During copulation, the male clasps the female with his first two pairs of legs. The robust femur and tibia (see leg segment diagram) on each of these legs are studded with a double row of tubercles, giving them a serrated look.

Male N. magna. Note the burly front legs, presumably modified for grasping the female (photo Sean McCann).

Although the female may attempt to disengage from her partner, he is able to maintain a firm hold with his rather spectacularly modified legs and continue copulation.

Female N. magna, with slender front legs (photo Sean McCann).

Fun with etymology: The genus name Neoantistea means “new Antistea”. Antistea comes from the Latin word antistes, which means “one who stands in front of a temple, overseer, high priest”. Why were these tiny spiders given such a grandiose name? It’s a mystery.

References

Engers, W., & Bultman, T. (2006). Foraging Habits of Neoantistea magna (Araneae: Hahniidae).

Gardner, D., & Bultman, T. (2006). Natural History and Reproductive Biology of a Hahniid Spider in Southwestern Michigan.

Opell, B. D., & Beatty, J. A. (1976). Nearctic Hahniidae (Arachnida: Araneae). Bull Mus Comp Zool Harvard Univ.

Tetragnatha revisited: dinner and romance at sunset

Posted on July 4, 2014 by cataranea

This post features photographs by Sean McCann. For more beautiful photography and natural history of arthropods and other wildlife, check out his blog, Ibycter.com.

As a sequel to our recent encounter with some long jawed orb-weavers in the genus Tetragnatha (the tiny and cryptic Tetragnatha caudata), this week on an evening walk at Iona Beach, Sean and I observed some neat predation and mating behaviour in another species, most likely Tetragnatha laboriosa.

We made our first observation just as the sun was beginning to set, the beginning of the most active hunting hours for Tetragnatha laboriosa. This female had just captured her first meal of the evening, a bug in the family Miridae.

After biting it, she began wrapping it with silk, which she pulled out of her spinnerets with her last pair of legs (you can see her caught in the act below).

After wrapping the bug lightly with silk, she carried it back to the hub of her orb web and settled down to dine.

Unfortunately for the spider, dinner was interrupted by Sean’s efforts to get a good photograph. The disturbance prompted her to drop her meal and retreat to the vegetation at the edge of her web. Isn’t she just gorgeous?!

After a minute or so, she went back for her abandoned prey.

She then carried it off the web to resume her meal in peace. You can see from this image how the lovely coloration of these spiders allows them to blend in with plant stems when they adopt their cryptic stick-like posture.

Later, when the sun had all but set and we were just about to head home, Sean spotted a pair of spiders (probably the same species, T. laboriosa) mating in a female’s web.

Mating involves a fair bit of contortion for long jawed orb-weavers. Below you can see the male’s extremely long pedipalp (one of a pair of appendages modified for transferring sperm) engaged with the female’s epigyne (genital opening). The male’s short third pair of legs is used to position his partner’s abdomen. Throughout copulation he maintains a firm grip on the female’s jaws with his own.

Here is a closer look at the mating position, where if you look closely you can see one of the female’s fangs interlocking with the special tooth on the male’s corresponding chelicera.

Here is a drawing by B. J. Kaston of what the cheliceral embrace looks like close-up. The male, with larger jaws, is below, and the female above.

Fig. 876 from Kaston 1948. Interlocking jaws of Tetragnatha pallescens (which looks very similar to T. laboriosa) during mating.

The female’s fangs get locked in underneath the special large tooth that protrudes from each of the male’s chelicerae.

As if we hadn’t had enough excitement already with the chance to closely witness such an intimate encounter, moments later we spotted two additional males waiting in the periphery of the female’s web. We were in for quite a show!

Here is one of the males that was waiting in the wings, posing elegantly and displaying his long jaws and even longer pedipalps. We’ll call him bachelor #2.

Not long after we spotted them, one of the lurking males made his move, lunging at the mating pair with his jaws held wide.

A bit of a tussle ensued, after which the mating spiders disengaged. The attacking male pursued the mated male off the web and all the way to the substrate below. The female, apparently rather perturbed by this rude interruption, also left the web. One of the two rival males, apparently dominant, soon ascended back toward the web via his dragline.

Just as the winner of the first brief battle returned to the web, the third male entered the ring, and a second chase ensued. This cycle repeated a couple of times, until at last only one male returned victorious to the periphery of the web.

Bachelor # 2 (or was it #3?) settled down to wait at the edge of the web, while the female made her way back to the hub.

It turns out that female T. laboriosa only mate once as a rule, and if copulation is interrupted as we observed, it’s a toss-up whether or not she will be willing to pick up where she left off (LeSar & Unzicker 1978). We couldn’t stay to see if our champion was able to successfully mate, but we wished him the best of luck!

Long, cryptic spiders

Posted on June 17, 2014 by cataranea

Iona beach, near the Vancouver International Airport in Richmond, BC, is fantastic place to go looking for spiders and other arthropods, and there always seems to be something new to discover on the dunes. So it was an unusual situation when last Friday evening, just before the park gates were about to close, Sean was lamenting not having found anything very interesting to photograph. We decided to spend our last minutes on the beach in an effort to turn up some sleeping hymenopterans in the vegetation bordering a walking path. After closely inspecting a couple of plants, instead of a sleeping bee or wasp, I found what at first glance looked like a tiny twig hanging in the middle of a spider’s orb web. Meet Tetragnatha caudata, the longest, most cryptic orb-weaver I have ever met!

This slender female was not easy to spot among the grasses, even though she was hanging right in the middle of her web. Her body is only about 1cm long from tip to tail.

Tetragnathidae is the family of the longjawed orb-weavers. You can see where the name comes from in the photo of a male below. During mating, the male and female interlock their large chelicerae in toothy embrace. This is where the male’s exceptionally long pedipalps come in handy, allowing him to reach the female’s epigynum while maintaining his hold on his partner’s fangs.

You can see this male’s large, powerful jaws sticking out to the sides underneath his very long, slender pedipalps.

Spiders in the genus Tetragnatha are sometimes called ‘stretch spiders’ because of their elongated bodies. They often rest with their first two pairs of legs stretched out in front. They can be very cryptic in this posture, especially if they cling to twigs or stems that are similar in colour to their bodies. Although they normally use their webs for hunting, sometime Tetragnatha will also snap up unsuspecting prey when lying low like this on vegetation.

A male Tetragnatha in camouflage mode. This works better on dry grasses or twigs, I would think. But still pretty stealthy here.

Most species in the genus Tetragnatha are difficult to tell apart, but I got lucky with this one (it keys out in the second couplet of the key to the Canadian species in this genus). Tetragnatha caudata is so named because of its strange looking abdomen (caudata means ‘tailed’ in Latin). While I would expect the spinnerets to sit at the tip of a spider’s abdomen, in this species there is a slight kink where the spinnerets sit on the underside of the abdomen, and a pointy tail sticks out behind them.

If you look closely you can see a strand of silk coming out of this female’s spinnerets, located on the underside of her abdomen just before it bends into a pointy tail.

The orb webs of Tetragnatha are usually horizontal or angled (unlike the vertical webs of spiders in the more familiar orbweaver family Araneidae) and have a hole in the centre where the spider sits waiting for prey.

We found several of these tiny Tetragnatha caudata among tall grasses, but larger members of the genus typically build their horizontal orbwebs over water, allowing them to capture insects such as mosquitoes as they emerge.

So let this be a lesson: next time you’re out looking for wildlife, stop and take a careful look in some seemingly boring vegetation! You never know what wonders you might turn up.

Thanks to Sean, as usual, for the great photos!

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

Bradley, R. (2013) Common Spiders of North America. University of California Press, University of California Press, Berkeley and Los Angeles.

Dondale, C. D., Redner, J. H., Paquin, P., & Levi, H. W. (2003). The Insects and Arachnids of Canada. Part 23. The Orb-weaving Spiders of Canada and Alaska (Araneae: Uloboridae, Tetragnathidae, Araneidae, Theridiosomatidae). Ottawa, NRC Research Press.

spiderbytes

This is a blog about spiders (and other arachnids)