The great black widow race: how males use the silk road to find females faster

I am very excited to share the publication of a new paper coauthored with Sean McCann and my supervisor Maydianne Andrade in the journal Proceedings of the Royal Society B. The full paper can be found here (please email me or contact me on twitter if you don’t have access and would like a pdf copy). Before I summarize the study below, I would like to first thank the Tsawout First Nation for allowing me and my collaborators to study black widows on their beautiful lands for the last several years. We also offer heartfelt thanks to the many generous contributors* to our #TeamBlackWidow crowdfunding campaign, without whom this research would not have possible. Finally, we are also very grateful to the Toronto Entomologists’ Association for funding part of the fieldwork with the Eberlie Grant, and to NSERC for funding our lab’s research and my PhD program.

Female (left) and male (right) western black widow spiders (Latrodectus hesperus). Photo: Sean McCann

For solitary animals that reproduce sexually, finding a partner is a critical first step in the sequence of events that lead to mating. We know a lot about the traits that help males win fights over females (like horns and other weapons), as well how female preferences can lead to the evolution of extravagant ornaments and displays like the tails of male peacocks (or peacock spiders). But these two mechanisms of sexual selection (male competition and female choice) can often only operate on males that actually find females to compete over. In a lot of animals, including many terrestrial arthropods like insects and spiders, a race to find females determines which males get the opportunity to pass on their genes. The kinds of traits that help males to win this race are less well understood than male ornaments and weapons, in part because it can be tricky to track mate searching males in nature.

Our field site on the sand dunes of southern Vancouver Island, British Columbia. At this site, driftwood logs provide shelters for western black widows. Photo: Sean McCann

In this study, my coauthors and I used experiments and observations of the natural movements made by black widow males to learn more about what gives them an edge when it comes to finding females. First, we spent about six months in the field tracking hundreds of male black widows in their natural habitat. We marked all of the females (who generally stay put on their capture webs, which makes them relatively easy to keep track of) and males (who actively search for females) that we encountered during the season. This allowed us to estimate how many males survive the trip to find females (only about 12%!) and how far they move when they do survive (in most cases, less than 60 metres, but sometimes more than 200, which is pretty impressive for spiders with a body length of less than 1 cm!). We were also able to determine that males outnumber receptive females by more than 10 to 1 during the height of the mating season, which means that competition over mates is fierce, making traits and tactics that confer an advantage to searching males all the more important.

We spent a lot of nights on the beach checking the webs of marked females, marking and recording any males who visited them. Photo: Sean McCann

Before we get to those tactics, however, let me back up for a minute and summarize some important features of black widow sexual communication and behaviour that are relevant to this story. First, female black widows produce a sex pheromone that functions as a chemical personal ad. This chemical message is released from the silk of a female’s web, and it provides males with information about her location and sexual receptivity. Before this study, we didn’t know the range of this message, just that it operates over some distance, allowing males to locate females who are ready to mate. Male black widows detect the female’s pheromone using sensory hairs on their legs. Once a male finds a female, he engages in a courtship dance that transmits vibrations through her web, providing her with information about his identity and quality as a mate. After several hours of dancing and laying down silk all over the web and the female’s body (this silk may contain chemical messages just like the female’s), and assuming he is not interrupted by a rival or eaten by the female (it happens, particularly if she’s hungry and therefore more interested in a meal than mating!), the male eventually mates with her. Spiders do this in a strange and unique way, transferring sperm with paired copulatory organs called pedipalps. The first male to mate can break off the tips of his copulatory organs inside the female, effectively blocking rival males from inseminating her, and thus ensuring his paternity.

A female (yellow 567, whose number corresponds to the location of the paint marks on her legs) consumes an unlucky male. Photo: Sean McCann.

Ok, now back to the research! The experimental part of our study involved setting up a series of actual races for male black widows—first longer-distance contests in the field, and then shorter sprints in the laboratory. For the great black widow races of 2016 and 2017, we set up a 60-metre course on the sand dunes at our field site. The finish line was made up of a series of mesh cages containing females and their silk.

The finish line of the 2016 great black widow race. Each cage contains a female black widow on her pheromone-emitting web. Photo: Sean McCann

Before the race, we weighed in each male on a tiny scale**, measured the length of his legs, and painted him with unique racing stripes so we would be able to track whether he completed the race and calculate his average speed. At sunset (black widows are nocturnal, so males search for females at night) we released groups of about 20 males at 10 metre intervals from the finish line, so that the closest group only had to travel 10 metres and the farthest group had to travel 60 metres. The course was set up so that males would be downwind of the line of pheromone-emitting females (assuming that the forecast was correct), and once all of the males were released, we waited at the finish line for them to start arriving outside of females’ cages.

A green-marked male crosses the finish line! Photo: Sean McCann

In 2016, when the wind was strong and came fairly consistently from the forecasted direction, males released at all distances up to 60 metres were equally likely to find females, which suggests that they are very sensitive to the smell of females. In 2017, however, when the wind ended up being weak and highly variable in direction, males released farther than 40 m from females were never able to locate them. Clearly, wind speed and direction will strongly affect the ability of a male to detect and find a female using only their sense of smell. But these experiments also revealed something surprising. In 2016, we found that the males that started out farthest from females achieved the fastest average speeds during searching—up to almost 1.5 metres (or more that 150 body lengths for spiders that are typically less than 1 cm long) per minute! And in 2017 we found that not only were males able to reach the finish line even after the wind shifted so much that smelling females on the racecourse was likely impossible, but also that the vast majority of males ended up outside of the cage of the single female who was in line with the direction of the wind during the first couple hours of the experiment.

A yellow-marked male makes his way down the race course. Photo: Sean McCann

Spending time watching what these spiders actually do when they search for females helped us make sense of these results. Male black widows have very poor vision, so they are guided toward females by their sense of smell. To get their bearings, they climb up vegetation, and wave first pair of legs (which you’ll recall are covered with sensory hairs), apparently ‘tasting’ the wind. After a while, they will climb back town to the ground and continue to move toward their target. Like all spiders, male black widows trail silk draglines behind them as they move through their environment. They anchor these safety lines to the vegetation periodically, such that they leave a silk path wherever they go. We noticed that when a searching male encounters one of these trails, he runs along it, using it like a silk highway. We realized that if males recognize the silk of rival males, they may use their trails to find females, even if wind conditions make it difficult to smell a female directly. And since these spiders are much more adept at walking on silk than on the ground, this might explain why the males in our experiments who traveled farthest also traveled fastest. The males released at 60 metres would have been most likely to encounter the silk trails left behind by all those who were released closer to the females.

A white-marked male has climbed up some grass and is extending his forelegs to taste the air for female pheromones. Photo: Sean McCann

To test this idea directly, we next ran a series of experiments that we called the X-races, the first of which was carried out by students in the behavioural ecology class Sean and I taught together at UTSC in 2017. The race course in this experiment is an X-shaped maze made out of string, with a female set up at one end with a fan behind her to blow her pheromone toward the male, who is released on one of the short arms of the X at the end opposite the female.

The X-race, an experimental setup for testing whether males follow or avoid the silk of rival males.

After being placed on the string, he moves upwind and when he reaches the centre of the X, he can choose to follow either arm—both lead to the female, and either way, he leaves a trail of silk behind him. Next, we introduce a second male to the end of the maze farthest from the female, but on the opposite arm from the first male. When this male gets to the intersection of the X, he now has a choice to follow or avoid the silk of the rival male. We used this experimental set up to confirm that males follow the silk of rivals when given the choice, and that they travel faster when they do. Using a modified version of the X-race, we also found that males only follow the silk of other black widows (and not that of closely related false widow males, who also occur at our field site), which means that the information on the silk is species-specific.

Sean (foreground) and our 4th year behavioural ecology students set up an X-race in the lab. The trays of water below prevent the spiders from leaving the maze if they drop down on a dragline.

When we put all this together, it tells us that male black widows use the somewhat surprising tactic of following their rivals to find females faster, and that exploiting the silk trails produced by earlier searchers allows them to locate females efficiently even when conditions make it difficult to directly detect their chemical messages. It might not seem like a great idea to follow another male to a female’s web, because this guarantees a competition over the opportunity to mate with that female. We would expect male animals to use cues about the presence of rival males to avoid competition, when given the choice (and in at least one other spider species, they do). But our time following this population in the field revealed that these males are unlikely to ever have that choice. There are so few sexually receptive females signaling on any given night that competition is inevitable. In this situation, the best tactic for males may be to arrive at a female’s web as fast as possible, even if other males are already there. Although being the first male to mate is important for black widows, being first to arrive is not critical, because courtship may last several hours. It’s at this point, at the female’s web, that competition and female choice can finally kick in.

Two males who have arrived at the same female’s web one after the other. Photo: Sean McCann

We are excited about these results, which reveal a surprising means of using indirect information to gain a competitive edge in the race to find females. We are also hope that our experimental race designs can allow us and other researchers to learn about spider mate searching behaviour and chemical communication in the future. Setting up races over different kinds of terrain to look at the effects of physical barriers on male performance, or doing races over several days and longer distances could yield more insights into what traits are important for searching males. Longer distance ultramarathons for spiders might be more appropriate in environments where females are more widely dispersed than at the site we studied. And the X-race is a convenient way to test male decision-making under controlled laboratory conditions while using a setup that reasonably reflects how male spiders actually move in the field.

This is only the first chapter of black widow behaviour research brought to you by the support of #TeamBlackWidow, and we look forward to sharing the next instalment soon!

*^ Thank you SO MUCH to Catherine & Doug Antone, Joe Lapp, Robb Bennett, Roy Dunn, Sean Lambert, Betty Kipp, Dora Sardas, Kristen Cain, Christy Peterson, Christy Peterson, Raphael Royaute, Dawn Bazely, Woodrow Setzer, Pierre Robillard, John Barthelme, Nemo de Jong, Mike Boers & Tanya Stemberger, Sina Rastegar, Sarah Langer, Sidnee & John Scott, Stephen & Linda Lambert, Staffan Lindgren, Amanda Yee, Rob Higgins, Tonia Harris, Tanya Jones, Joe O’Franklin, Dezene Huber, Tracey Birch, Peggy Muddles, Regine & Gerhard Gries, Gwylim Blackburn & Samantha Vibert, Alex & Karla Antone, Gil Wizen, Gwen Pearson, Joan Andrade, Kate Compton, Peggy McCann, Peter Andrade, Rick Redus, Robyn Raban, Shelley Barkley, Stewart, Geoff Bennett, Kyle Cassidy, Colin & Heather McCann, Jonathan Meiburg, Lori Weidenhammer, Diana Davis, Ray Scanlon, Ashley Bradford, Ed Morris, Robert Cruickshank, Marc Rashinski, James Petruzzi, Joseph Peter McNamara, Ariel Ng, Robert Neylon, Auriel Fournier, Victoria Nations, Leah Ramsay, Tom Pearce, Chloe Gerak, Scott Severs, Angie Macias, Nick Spencer, Thomas Astle, Luna Nicolas Bradford Ley, Peter Midford, Laurel Ramseyer, Morgan Vis, Tom Pardue, Scott Schrage, Kelly Brenner, Karen Yukich, Charmaine Condy, Amy Parachnowitsch, Catherine Scott, Christine Rock, Jason Parker-Burlingham, Jonathan Kade, Joseph Peter McNamara, Joshua Erikson, Juniper English, Nick Spencer, Robert Cruickshank, Sabrina Caine, Suran TheStorm, Richard Dashnau, Stephen Heard, Holly Fraser, Lynne Kelly, Roberta Chan, Kat Cruickshank, Meera Lee Sethi, Mike Hrabar, Tiffany Jacobs, Connie Larochelle, Willow English, David Steen, Michelle Reeve, Tone Killick, David Esopi, Antonia Guidotti, Elaine Wong, Lisa Wrede, Naomi Gonzales, Don Campbell, Matt Masterson, Paul Manning, Casey Peter, Dave Rich, Jessical Olin, Kate Rey, Katie Russell, Shari McDowell, Suzanne Spinelli, Christina Tran, Cindy Wu, Aaron Soley, Chris Garbutt, Greg Randolph,  Lila Robinwood, Eric Damon Walters, The Spider Chick, & Steve Waycott!!!

** ^Thanks very much to Jay Cullen at UVic for kindly allowing us and our spiders access to his lab and microbalance!

Science Borealis: vote for your favourite Canadian science blog!

I am honoured and a bit embarrassed to announce that SpiderBytes is in the running for the Science Borealis People’s Choice Award for “Canada’s Favourite Science Blog.” Honoured, because I am proud to be part of the Science Borealis network of Canadian science blogs! And embarrassed, because I have posted exactly two things here in the last year. In my defence, I have been in the thick of pursuing a PhD, but I will take this as a challenge to blog a bit more in the upcoming year (my final one, if all goes well, as a PhD student!).

A male black widow engaged in web reduction behaviour, one of my favourite ways male spiders use silk during mating interactions. This is one of several behaviours featured in the first paper of my PhD thesis. Photo: Sean McCann.

Despite only adding one new post this year, a lay summary of the first paper of my PhD thesis (a review of all the weird and wonderful was male spiders use silk during courtship and mating), the blog has seen a lot of traffic since last September. The vast majority of views (averaging about 10,000 per week) have been visits to the Recluse Or Not page and the associated post How to tell if a spider is not a brown recluse. I am very pleased with the traction that the Recluse or Not project (a collaboration with my wonderful colleagues Matt Bertone and Eleanor Spicer Rice), has gotten both here and on twitter and it makes me feel a little less sheepish about being nominated!

Header image for our Recluse or Not page illustrating some of the many spiders that are commonly mistaken for recluses in North America. From left: yellow sac spider, running crab spider, male southern house spider, brown recluse. Photos: Matt Bertone.

Please go vote for your favourite blogs (see all the nominees here) and thanks very much for stopping by! I’ll endeavour to add some more content in the upcoming months since it’s prime time for spiders here in Vancouver!

 

Spider sex and silk: From mating threads and bridal veils to nuptial gifts and silk-lined chambers

I am very pleased to announce the publication of a review paper in the Journal of Arachnology (check out the full pdf here) about the fascinating uses of silk during spider sexual interactions coauthored with Alissa Anderson and my supervisor Maydianne Andrade. This paper has been several years in the making, and some of my very first blog posts were based on the research I did when I first started writing it back in 2013 as part of a reading course for my MSc degree.

Pisaurina mira (a nursery web spider in the family Pisauridae), one of the many diverse species featured in our paper, and the focus of my coauthor Alissa’s PhD research (photo: Sean McCann).

Overview

In this paper we describe the many weird and wonderful ways that male spiders use silk during courtship and mating. Little experimental work has been done to determine the function male silk in sexual interactions, but the available research suggests that in general silk use improves the male’s chances of mating with a particular female or reducing the risk that she will mate with other males. There is also mounting evidence that silk-bound sex pheromones are commonly produced by male spiders (though much less well studied than female silk pheromones), which may help to explain the importance of silk production during sexual interactions in many species. In the paper, we divide male silk use into three categories, briefly summarized below.

  1. Silk deposition on the female’s web or other silk structures

Figure 2 from the paper. Examples of silk deposition onto females’ webs during courtship. (a) Araneus diadematus (Araneidae) male and female hanging from the male’s mating thread, attached to the periphery of the female’s web (photo: Maria Hiles). (b) Web reduction with silk addition by a Latrodectus hesperus (Theridiidae) male. The male has dismantled part of the capture web (which would have filled the lower half of the photograph before he began web reduction behavior) and is wrapping it with his own silk (photo: Sean McCann).

The most common and widespread form of silk use during sexual interactions across spiders is simply the deposition of silk on the female’s web or the silk surrounding her burrow entrance. More elaborate use of silk includes the installation of silk mating threads or webs on which courtship and copulation take place and web reduction, which can result in extreme modification of web architecture. The few experimental studies of this kind of silk use indicate that it is involved with preventing females from mating with other males, as in black widows. However, it is likely that mating threads and webs generally function to improve male mating success by improving transmission of their vibratory courtship signals and/or to reduce the likelihood of sexual cannibalism.

  1. Silk bondage: the bridal veil

Figure 3 from the paper. Examples of silk ‘bridal veils’ applied to females’ legs and bodies during courtship. (a) Nephila pilipes (Araneidae) male depositing silk onto the female’s carapace, legs, and abdomen (photo: Shichang Zhang). (b) Xysticus cristatus (Thomisidae) female with silk on her forelegs and abdomen as she feeds on a prey item—note that the male is underneath her abdomen (photo: Ed Niewenhuys). (c) Latrodectus hesperus (‘‘texanus’’ morph, formerly Latrodectus mactans texanus; Theridiidae) male depositing silk onto the female’s legs (photo: Sean McCann). (d) Pisaurina mira (Pisauridae) male wrapping a female’s legs with silk prior to sperm transfer (Photo: Alissa Anderson).

The “bridal veil” (which I’ve previously written about in detail here) describes the silk some male spiders wrap around females prior to copulation. Arachnologists have debated the function of this behaviour for many years but it has been generally assumed to prevent sexual cannibalism. In some species like the nursery web spider Pisaurina mira, the silk wrapping physically restrains the female, giving the male time to escape while she struggles free of her bonds. In the orb-weaver Nephila pilipes, on the other hand, tactile cues and chemicals on the silk have been implicated in reducing the female’s aggressive tendencies. In both species, males that wrap females with silk are able to transfer more sperm to females, improving their mating success. Bridal veils are used by males from at least 13 families of spiders, including both web builders and wanderers, and there is still much to learn about the function of this fascinating behaviour across the diverse species that use it. In one species of wolf spider, the female even eats the silk of the veil after mating, which brings us to the third category of male silk use.

  1. Silk wrapped nuptial gifts, or the gift of silk itself

Figure 4 from the paper. Examples of silk-wrapped nuptial gifts. (a) Female (right) Pisaura mirabilis (Pisauridae) accepts a silk-wrapped gift from a male (photo: Alan Lau). (b) A male (right) Metellina segmentata (Tetragnathidae) has wrapped a rival male in silk as a nuptial gift for the female (photo: Conall McCaughey).

In two families of spider, the nursery web spiders (Pisauridae) and their close relatives the longlegged water spiders (Trechaleidae) males present females with silk wrapped prey items called nuptial gifts (which I previously wrote about here). Sometimes, though, the silk package actually contains non-food items like rocks or plant material. The silk itself seems to be the important thing for getting the female to accept the gift and grasp it in her jaws, keeping her busy (and the male safe) during copulation. Both visual signals associated with the colour of the silk and chemicals on the silk may be important ways that gift-giving males communicate their quality and persuade females to mate with them, not to mention potentially deceiving them into accepting worthless gifts.

In other spiders gift-giving is less ritualized or happens only some of the time, like in the longjawed orbweaver Metellina segmentata. Males of this species often compete on the female’s web, and sometimes one of them will kill his rival, wrap him up with silk, and present him to the female. As with the habitual gift-givers discussed above, mating with the female while she is busy feeding on her erstwhile suitor likely decreases the male’s chance of becoming dinner. In still other spiders, the silk itself constitutes the gift, rather than the wrapping. In the ray spider Theridiosoma gemmosum, the male feeds the female silk directly from his spinnerets during courtship and copulation. This silk gift provides the female with nutrients (these spiders can recycle silk proteins). Finally, silk-lined burrows are considered gifts in the sex-role reversed wolf spiders Allocosa senex and A. alticeps. In these species, males dig deep silk-lined burrows to which they attract females with a pheromone. Mating takes place inside the burrow, and afterward the male helps the female to seal herself inside the burrow where she lays and broods her egg sac. The energy and silk that go into producing the burrow are a considerable investment for the male, and directly benefit the female and his offspring by providing a safe refuge.

The big picture 

Silk use during courtship occurs in diverse species all across the spider tree of life, and provides myriad opportunities for future research. In the figure below, many families are not highlighted, but this is as likely to represent lack of knowledge about their courtship behaviour (or even anything about their natural history) as lack of silk use, and I hope that this paper will inspire other arachnologists to investigate mating behaviour, silk use, and the potential for male pheromone production in some of these little studied spiders. There are undoubtedly many exciting new discoveries to be made and I look forward to reading about them and perhaps making some myself in the future.

Figure 1.—Cladograms illustrating relationships between araneomorph spider families (based on Wheeler et al. 2016) and the occurrence of male silk and pheromone use.  Note that in the Mygalomorphae (families not shown on the figure) there are records of male silk deposition on the female’s web or silk for species in the following three families: Dipluridae, Porrhothelidae, and Theraphosidae.

Full citation of the paper:

Scott CE, Anderson AG & Andrade MCB. 2018. A review of the mechanisms and functional roles of male silk use in spider courtship and matingJournal of Arachnology 46(2): 173-206. Open access here

Announcing a new project: Recluse or Not?

This is just a quick announcement about a new citizen science and education project called Recluse or Not?

A recluse spider (Loxosceles arizonica). Photo: Sean McCann.

Recluse or Not? is a collaboration with North Carolina entomologists Eleanor Spicer Rice (Dr. Eleanor’s Book of Common Spiders) and Matt Bertone that you can read all about on the project page here! Briefly, it is a way for citizens to contribute data about where in North America recluse spiders (genus Loxosceles) occur, and to quickly get suspected recluse spiders identified by an expert. We also aim to correct myths and misinformation by regularly tweeting facts about recluse spiders from our new twitter account, @RecluseOrNot.

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!

Steatoda grossa female

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.