Crowdfunding black widow research

For the past six months, Sean and I have been spending most of our nights observing black widows in their natural habitat on Vancouver Island, BC. We did a couple of short experiments during our time in the field, but the vast majority of our work involved simply observing the spiders as they went about their business. The goal was to get a better understanding of the natural behaviour and mating dynamics of this population. This kind of basic natural history research (as opposed to experiments designed to test specific hypotheses) is not often done because it can be challenging, time consuming, and expensive, and is looked on by some as not as important as hypothesis-driven research. I think this is a shame, because there is still so much waiting to be discovered if we only take the time to look. And it is easy to overlook amazing and potentially important phenomena if we don’t take that time. It’s also easy to make incorrect conclusions about the way the world works when we rely only on experimental data and don’t already have a good understanding of the natural history of the organisms we are studying.

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Sean and I doing black widow research at Island View Beach. Drone photo: Sean Lambert (used with permission)

Let me tell a quick story. You may recall that last year our study about web reduction behaviour in black widows was published. (Here’s a plain language summary of the research). Based on observations of sexual behaviour of black widows in the laboratory, we knew that males often engage in web reduction when courting on the webs of virgin female. The male cuts up sections of the web, bundles them up, and wraps them with his own silk. We wanted to know the function of this behaviour, so we ran some carefully designed experiments in the field, and concluded that web reduction allows males to avoid competition by decreasing the attractiveness of the female’s web. We assumed that this is a common tactic used by the first male to arrive at a female’s web, in order to avoid other males from finding the female and interrupting his courtship efforts. I was looking forward to learning more about web reduction this summer as we observed black widows behaviour across the course of a mating season. Guess how many times we observed web reduction in the field? Exactly once. All our laboratory observations were of males introduced onto the webs of adult females. It turns out that in the field, males mature before females do, and most of the time they arrive at a female’s web before she is sexually mature (and before she has the attractive chemicals on her web that trigger web reduction behaviour). Our previous results were not wrong, but without this year’s fieldwork we might never have realized that by focusing on sexual interactions between males and adult females we were missing a big part of the story. How males find immature females, and their behaviour once they do, is likely much more important for avoiding competition than web reduction. There is so much we still don’t know about black widows, that’s just waiting to be discovered!

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Male western black widow (Latrodectus hesperus) engaged in web reduction behaviour on an adult female’s web. Photo: Sean McCann

I feel extremely lucky to have had the opportunity to do this fieldwork as part of my PhD research. Spending six months in the field is very expensive, and a bit of a risk scientifically, because exciting results are definitely not guaranteed. I will likely not have the opportunity to do extended natural history fieldwork like this again, because funding for basic research is increasingly hard to come by. Government funding for science is more and more focused on applied work that has clear benefits for the public. The problem with this model is that future applications and benefits of basic research are often difficult to foresee.

In my case, there are some obvious potential applications of studying chemical communication in widow spiders. Some species are invasive or considered pests in certain areas (including vineyards in BC), so a way to control them without using harmful pesticides would be very useful. Once we understand how male and female black widows respond to one another’s chemical messages, and the identity of the chemical compounds involved, we may be able to develop ways of using these naturally occurring messages to trap and remove spiders from areas where they are a problem. Partly because of this, I think, I was successful in securing an NSERC scholarship to do my PhD (thank you Canadian taxpayers!!!) but even so, I am not exactly drowning in money to support my research.

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Female black widow on her web at Island View Beach. Photo: Sean McCann

The rest of my PhD work will take advantage of the excellent understanding we now have of how black widows actually behave in nature. I will be able to design laboratory experiments that are as naturalistic in context as possible, and use what we now know based on this year’s field observations to make well-informed conclusions. However, to really understand how chemical information affects black widows over the course of their development and their mating interactions, the best place to do the work (both experimental and observational) is in their natural habitat, and this is where the title of the post comes in.

If I had my wish, next summer I would go back to the field for four months (the full mating season) to do experimental and observational studies of black widows that will improve our understanding of their chemical communication. Our lab’s funding is sufficient to pay for travel to and from the field site and for the basic equipment we’ll need to do the research*, but there’s one problem. It’s simply not safe to do the work I have planned (often at night) alone. I will need a field assistant, and that field assistant will need a salary. (Volunteer field assistantships for this kind of work do happen, but they are bad for science, and not an option we would consider.) I can and will apply for several graduate student research grants, and if I am successful these will help defray the costs of the planned fieldwork. Unfortunately, most of these explicitly do not allow the funds to be used to pay salaries. That’s where you come in!

*UPDATE: Here is a note on our campaign page where my supervisor explains the funding situation and why we’re asking for money in a bit more detail.

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The logo and hashtag for the project. Logo designed by The Vexed Muddler.

For the next 30 days, Sean McCann (who was my field assistant this year, and who will continue to collaborate on the project one way or another), my supervisor Maydianne Andrade, and I will be running a crowdfunding campaign on Experiment.com as part of their Arachnid Challenge. We hope to raise the $6000 USD (the salary of a full time field assistant for four months) that we would need to make my plans for another season of black widow fieldwork a reality. This is an opportunity for anyone to support and participate in our research. If we are successful, we will post regular updates about our plans and progress, and share stories and photographs from the field.

Please check out the campaign page for more details, and consider donating. Even $5 will make a difference, and everyone who contributes will receive our heartfelt thanks and be acknowledged in all publications and presentations resulting from the research. If you donate $15 USD (about $20 CAD) or more, we are offering various tangible tokens of our very deep appreciation, including swag with our fantastic logo (designed by the brilliant Vexed Muddler) and prints of Sean’s beautiful photographs. Even if you cannot support the project with a donation, I would be so grateful if you would consider sharing the campaign with your friends and colleagues on social media, email, or in real life. The more people we reach, the more likely we will be to reach our goal!

Thank you so very much in advance for your support – we really appreciate it!!!

Spider Week on pause

You may have noticed that Spider Week has lost some steam here and on twitter. It was a fun idea that came at a time when I probably should have realized I already had a bit too much on my plate. Then more things got piled on, and I started to get sick. For now, spider week is on pause, but please expect posts on the remaining five spiders sometime soon!

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False widows in the genus Steatoda were the spider of the day on Tuesday, but I have not yet had time to write a full post on them. Photo: Sean McCann.

Fishing spiders (family Pisauridae)

Today’s featured spiders for Spider Week are the fishing spiders (also known as raft spiders) in the genus Dolomedes. I suspect the reason they are so often mistaken for brown recluse spiders is that they are (a) brown, and (b) often very large. Brown recluse spiders aren’t particularly large, but folks seem to (erroneously) associate size with danger when it comes to spiders.

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A large female Dolomedes tenebrosus from southern Ontario. Photo: Sean McCann, used with permission.

Fishing spiders are members of the family Pisauridae, commonly known as nursery web spiders. Female spiders in this family make excellent mothers. They carry their large silken egg sacs around in their chelicerae (jaws) until the spiderlings inside are just about ready to emerge. Presumably this means that females don’t eat at all during this time!

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Dolomedes female carrying her egg sac in her jaws. Photo: Ron Knopik, licensed under CC BY 2.0.

The spider then builds a nursery web in vegetation and suspends the egg sac inside. She stands guard until the spiderlings emerge. They remain in the nursery web for a while, undergoing one moult before setting out on their own.

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Nursery web spider guarding her nursery in New Zealand. Photo: Tony Wills, licensed under CC BY 3.0.

The large fishing spiders, including Dolomedes tenebrosus and Dolomedes scriptus are also sometimes called dock spiders or wharf spiders. They are typically found on or near water – often on human-made structures.

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Dock spider (Dolomedes tenebrosus) on part of a wooden wharf in Ontario. Photo: Sean McCann, used with permission.

As their common name suggests, fishing spiders make a living hunting for fish, tadpoles, and aquatic invertebrates. They can walk on water and even sail across the water’s surface either by lifting their front legs, or by standing up on ‘tip-toe’ to catch the wind.

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Six-spotted fishing spider (Dolomedes triton)resting on the surface of a pond in the Okanagan. Photo: Sean McCann, used with permission.

While hunting, fishing spiders typically rest with their back legs on floating wood or vegetation, and their front legs resting lightly on the water’s surface. This way they can detect surface waves on the water, allowing them to locate potential prey. If the spider detects a fish under the water, they use their back legs to push off and dive after it. Dolomedes triton also dives under water when disturbed – this may be a good way to avoid predators such as birds (or a scary human trying to catch them, which is how I first observed this behaviour). And they can stay under water for up to half an hour! They are able to breathe underwater because spider lungs are located on the abdomen, which is covered with fine hairs that trap air, forming a sort of diving bell.

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Fishing spider (Dolomedes tenebrosus) in hunting position on the water’s surface. Photo: Sean McCann, used with permission.

Notes on Identification

Fishing spiders are most likely to be confused with wolf spiders (family Lycosidae). The best way to tell them apart is the eye arrangement. Wolf spiders have three rows of eyes, with the forward-facing pair in the middle row (the posterior median eyes) very large, and the first row of four eyes in a straight line or slightly procurved (curved downwards).

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Wolf spider eye arrangement. Photo: Sean McCann, used with permission.

Fishing spiders have only two rows of four eyes each. Both rows are slightly recurved (curving upwards or toward the back end of the spider) and the posterior median eyes are not that much larger than the rest.

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Fishing spider eye arrangement. Photo: Sean McCann, used with permission.

References and further reading:

A dedicated mother (with fantastic photos!) by Alex Hyde

Canada’s largest spider by Chris Buddle

Pisauridae: Nursery web spiders by Africa Gomez

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

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

Carico, J. E. (1973). The Nearctic species of the genus Dolomedes (Araneae: Pisauridae). Bulletin of The Museum of Comparative Zoology, 144:435-488.

McAlister, W. H. (1960). The diving and surface-walking behaviour of Dolomedes triton sexpunctatus (Araneida: Pisauridae). Animal Behaviour,8(1-2), 109-111.

Nyffeler, M., & Pusey, B. J. (2014). Fish predation by semi-aquatic spiders: a global pattern. PLOS ONE, 9(6), e99459.

Suter, R. B. (1999). Cheap transport for fishing spiders (Araneae, Pisauridae): The physics of sailing on the water surface. Journal of Arachnology, 27:489-496.

 

 

Yellow sac spiders (family Eutichuridae)

The first spider of spider week, squeezing into the 7th-most-likely-to-be-misidentified-as-a-brown-recluse spot (despite not even being brown), is the yellow sac spider. This common name may be used to refer to multiple similar-looking species in the genus Cheiracanthium (family Eutichuridae).

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Cheiracanthium inclusum (female). Photo: Joe Lapp (also known as Spider Joe), used with permission.

In North America we have two species: Cheiracanthium inclusum (a native species) and  C. mildei (introduced from Europe). Other names for yellow sac spiders include black-footed spiders, long-legged sac spiders, and yellow house spiders. All are pretty good descriptive names, because Cheiracanthium are indeed long-legged, black-footed, and commonly found in houses. Cheiracanthium mildei is more often found indoors, whereas C. inclusum (also known as the agrarian sac spider) is more common outdoors in fields and foliage.

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Cheiracanthium male. Photo: Sean McCann, used with permission.

Identification: Yellow sac spiders are fairly easy to identify based on some distinctive features. They have relatively long legs, with the front pair of legs longer than the rest, and black “feet” (tarsi equipped with tufts of dark hairs that allow the spider to easily scale vertical walls). Overall colouration can vary from pale yellow or tan to light green or even sometimes orange or brown, depending on the spider’s diet. Typically there is a darker longitudinal stripe called a heart mark (because that’s where the spider’s heart is) along the abdomen. Although most folks don’t usually get close enough to count them, the eight eyes are all similar in size and arranged in two nearly straight rows. Sac spiders in the family Clubionidae are probably most likely to be confused with yellow sac spiders, but they have shorter, more robust legs, and the front pair is not longest.

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Cheiracanthium inclusum. Photo: Joe Lapp, used with permission.

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Cheiracanthium eye arrangement. Photo: Don Loarie, licensed under CC BY 2.0.

 

 

 

 

 

 

 

 

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Cheiracanthium male. Photo: Natalie McNear, licensed under CC BY-NC 2.0.

Natural History: Yellow sac spiders build silk ‘sleep-sacs’ in rolled up leaves (when living in the great outdoors) or where walls meet ceilings inside houses. They may rebuild these retreats every night just before dawn, and rest inside during the day.

Yellow sac spiders are active nocturnal hunters, but in addition to insects and other arthropods, they also feed on extrafloral nectaries of plants such as castor bean. Most people think of spiders as strict carnivores, but in practice many spiders have a more varied diet.

When a male finds a female in her sleep sac, they tap on the outside of the silk retreat (how polite!) and then start cutting the silk away from the entrance (less mannerly).

Myth-busting

For a time, Cheiracanthium was considered one of three ‘medically significant’ spider genera in North America, along with the recluse spiders (Loxosceles) and the widow spiders (Latrodectus). Their bad reputation turns out to be undeserved – they do NOT cause necrotic lesions like brown recluse spiders as was once thought. They do have a rather painful bite – like a bee or wasp sting – but the results of envenomation are not serious. Because they often live in close association with humans, bites from these spiders may be more common than spider bites in general, but still extremely rare. (There’s probably one or more in your house, and you’ve almost certainly never been bitten – you’d know it if you had!) Remember that spiders don’t bite humans except in very rare circumstances.

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Cheiracanthium sp. from in Illinois. Note that it is NOT biting, but rather trying to escape! Photo by Andrew Hoffman, licensed under CC BY-NC-ND 2.0. Check out his blog post about yellow sac spiders and the taking of this picture.

Another myth holds that these spiders are attracted to the smell of gasoline. Yellow sac spiders were responsible for the recall of several thousand cars but there is no actual evidence that they like the smell of gas.

References

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

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

Taylor, R. M., & Foster, W. A. (1996). Spider nectarivory. American Entomologist, 42(2), 82-86.

Vetter, R. S., Isbister, G. K., Bush, S. P., & Boutin, L. J. (2006). Verified bites by yellow sac spiders (genus Cheiracanthium) in the United States and Australia: where is the necrosis? The American journal of tropical medicine and hygiene, 74(6), 1043-1048.

More blog posts about yellow sac spiders:

The Ceiling Spider by Chris Buddle

Blame it on the sac spider by Andrew Hoffman

Longlegged sac spiders by Bug Eric

Announcing Spider Week

Starting tomorrow, Shark Week begins on the Discovery Channel. If you prefer spiders to sharks (which, of course you do, right?!) and facts to fearmongering, here at Spider Bytes and on twitter we’ll be celebrating #SpiderWeek!

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Here’s the plan: starting tomorrow (Sunday June 19), each day will feature a different spider family. These seven families will be chosen from among the most-misidentified spiders on twitter, based on the data I collected last year from my first several months of my #NotABrownRecluse campaign. (Here’s how to tell if a spider is not a brown recluse – tell all your friends!)

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A brown recluse spider we found in Texas. Photo: Sean McCann.

The top seven families will be featured in ascending order, starting with the 7th-most-often-mistaken-for-a-brown-recluse and ending with the number one most often misidentified spider-that-is-not-a-brown-recluse. Each day I will ask folks on twitter to guess which spider is coming next (points will be awarded!) and then I will post a blog entry about the day’s spider family. I’m not sure yet what they will be, but prizes will be awarded at the end of the week. Follow along here and on twitter, and be sure to ask questions and to contribute your own facts, photos, and suggestions through either medium! The goal is to celebrate spiders and learn something about their biology and how to identify them.

Get ready for some serious spider-related fun and facts, and have a fantastic Spider Week!

 

Zora & Syspira: wolf-like prowling spiders

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

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

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Not a wolf spider. Photo: Sean McCann.

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

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

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

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

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

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

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

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

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

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

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

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

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

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Female Syspira sp. Photo: Sean McCann.

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

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

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

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

Rhomphaea: ridiculously long theridiids

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

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

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

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

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

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

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

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

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

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

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

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

References & further reading

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

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

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

 

Oecobiidae

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Oecobius sp. from Scarborough. Photo: Sean McCann

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

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

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

References

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

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

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

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

A quick survey

Dear readers,

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

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

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

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

Myrmecophilic spiders

Myrmeco = ant; philic = loving

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

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

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

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

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

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

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

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

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References: 

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

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

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