Meet the spiders in your house with Travis McEnery!

Have you ever found a spider in your home and wondered whether or not you should evict it? If you are a dedicated arachnophile, perhaps you peacefully coexist with spiders no matter their size or habits. But not all spider housemates are equally polite, and you may want to be a little more selective about which spiders you accept as tenants. Some important considerations include the following: Will they make messy cobwebs and leave prey remains around the place, or are they tidy and discreet? Do they hang out in their webs all day, or move around the house, popping up in unexpected places to startle you with erratic movements? And is there any risk of the spiders defending themselves by biting human, feline, or canine members of the household? 

The answers these questions (and many more) can be found in the outstanding new youtube series The Spiders in Your House created by “amateur” arachnologist Travis McEnery. This post is an introduction to the series and Travis. I am a huge fan of both, and you should be too! 

One of Travis’ first videos, focused on the Common House Spider (Parasteatoda tepidariorum).

These videos are deeply researched, thoughtful, and often hilarious profiles of spiders that you can probably find in or around your own house. I am continually impressed by Travis’ ability to get to the bottom of questions about the spiders he covers. I put “amateur” in scare quotes above when describing him because Travis’ approach to arachnology and the videos he creates is anything but. As a professional arachnologist myself I have learned something new in almost every video (like what was really behind that Mazda recall blamed on yellow sac spiders!), and Travis is directly contributing to spider science through original observations and experiments (he is the creator of my new favourite experimental method for assessing spider biteyness: the cheese test).

Hit play on this video to see the cheese test in action, but definitely also go back to the beginning and watch the whole thing! This episode on yellow sac spiders is just fantastic.

Through his videos, Travis is breaking down barriers between lay people, casual arachnofiles, and professional arachnologists by not only presenting information from the scientific literature in a fun and accessible way, but also by going directly to the scientists behind the studies to get additional context on their findings and sharing what they have to say with the audience. Also, the theme song absolutely slaps.

Click play to hear the theme song.

Another reason I love Travis’ work on this series is that he is constantly learning and sharing that process with the audience. When a fellow arachnologist pointed out a small mistake in one of his videos (on the false widow spiders), he made a whole new video correcting it and in the process shone a light on the messiness of science (we all make mistakes, all the time, and learning from them is a big part of science!) and the value of open communication, collaboration, and a supportive community. This ended up being one of my favourites!

The video correcting a mistake in the episode on false widow spiders.

Head over to Travis’ youtube channel for more excellent videos, consider subscribing, and let him know what you think in the comments! He is super responsive to questions and suggestions, and I am sure you will enjoy learning from him as much as I do! You can also support him and find even more content on his Patreon.

For a bit more information on Travis and his motivation for the series, here’s a piece in The Globe and Mail in which I also appear (talking about the spread of misinformation about spiders). I often lament the lack of factual information about spiders on the internet, and I am extremely happy to see Travis contributing such excellent content and the overwhelmingly positive response to it.

They mostly come at night… mostly.

This post is not about aliens, but it is about the night-time marauding behaviour of fierce, many-limbed* predators: candy-striped spiders!

I am very excited to share this new paper that was a collaboration with my partner in life and science, Sean McCann! It’s the shortest paper I’ve ever written, and also my favourite scientific contribution so far. Written in a style that I hope is engaging and accessible, it documents some of the fascinating natural history of candy-striped spiders in North America. It is very short, so I encourage you to go read it in its entirety! Here I will present some back story and behind-the-scenes photos of what went into this study about the foraging behaviour of these intrepid spiders.

It all started with Sean’s penchant for getting up before dawn to take pictures of sleeping insects like these cuckoo leaf-cutter bees:

A pair of sleeping Coelioxys against the sunrise.

While we were doing fieldwork as part of my PhD research on black widow spiders on the lands of the Tsawout First Nation on the Pacific Coast, we had a mostly nocturnal lifestyle, but occasionally we would head out to our coastal dune field site early in the morning for some recreational spider and insect observations and photography. While searching for sleeping insects for Sean to shoot, we started to notice that wasps and bees would often be perched on dead vegetation in large aggregations like the one below.

A group of sand wasps (Ammophila sp.) sleeping together on a communal perch. Photo: Sean McCann.

Sometimes multiple species of wasps and bees would be sleeping together on the same dead plant. The stems used for perches were typically isolated from other vegetation, and we started to wonder about the sleeping habits of these insects. Does perching together in large groups reduce the risk of being taken by predators? Do the same bees and wasps come back to sleep together at the same perch night after night?

Cuckoo leaf-cutter bees (Coelioxys), sand wasps (Ammophila) and a lone thread-waisted wasp (Prionyx) all perched together before dawn.

We decided we would do a little project to try to find some answers. We located a few communal perches within our widow spider study area that we could visit each night during our regular surveys. Then we painted all the insects sleeping on the same perch with a dot of the same colour of paint, so we would recognize them if they returned.

Painting wasps at the pink perch.

Then over the next few nights, we returned to the perches to count the number of painted insects and new arrivals.

Counting wasps.

Soon, our ideas about safety in numbers were put to the test. We started to find our bees and wasps being picked off by spiders! In one case (shown below) a single sleeper of a group of 5 was captured and killed by a spider in the night.

A candy-striped spider feeding on an unlucky sand wasp while its perch mates sleep on, apparently blissfully unaware of the horror below.

In other cases however, we came upon perches whose whole cohort of sleepers had been massacred by a single spider! Now our curiosity turned to the behaviour of the spiders, who we suspected were able to subdue these large, otherwise well-defended (with venomous stings) prey by sneaking up on them while they were sleeping and too cold to defend themselves.

A death scene at dawn: the results of nocturnal marauding by a candy-striped spider (Enoplognata sp.). Photo: Sean McCann (Figure 1 from Scott & McCann 2023)

We now wanted to know who these spiders were, and what was known about their predation behaviour. The details are all in the paper, but the short version follows.

Candy-striped spiders (Enoplognatha ovata and E. latimana) come in three colour forms.

Candy-striped spiders are introduced to North America from Europe, and they can be extremely abundant in many habitats. They come in three colour varieties, and while the genetics of this polymorphism has been worked out, not much attention has been paid to their behaviour. Most of what we know about their predation is based on the observations of William Bristowe, an English naturalist who studied about these spiders almost 100 years ago. He described the following foraging tactics:

Web-based ambush. Like other members of the family Theridiidae, candy-striped spiders build messy tangle webs, often under flowers. When day-flying insects land on the flowers to feed on nectar and make contact with her silk threads, the lurking spider will rush out to wrap the prey with strong, sticky silk.

A candy-striped spider with a sparse tangle-web under yarrow has captured a wasp that landed on the flowers to feed on their nectar.

Web invasion for kleptoparasitism (stealing prey) and araneophagy (spider-eating). Sometimes, candy-striped spiders connect their webs to those of neighbouring spiders to eavesdrop on the vibrations produced by prey insects. At our field site, they would often have lines connecting their webs to those of black widows, and creep onto the web to try to steal prey from their much larger relatives (black widows are in the same family of tangle-web weavers: Theridiidae). They also sometimes eat the spiders themselves!

A very bold candy-striped spider whose web connects with that of her neighbour, a black widow, attempts to prey on both the web owner while she is in the process of wrapping a large spider (a male foldingdoor spider, Antrodiaetus pacificus) recently caught in her web. This attempt was ultimately unsuccessful.
Here a candy-striped spider preys on black widow spiderlings before they have a chance to disperse from their mother’s web.

More recently, candy-stiped spiders have been reported actively foraging without the aid of a capture web. A very cool study found that the spiders eavesdrop on the vibrations produced by sexually signalling leafhoppers and use these to locate these insects as they move around in grasses and shrubs.

A candy-striped spider with a pair of froghoppers taken without a web. Perhaps she located these individuals based on listening in on their vibratory duet as she prowled around on the leaves.

Launching sneak-attacks on sleeping insects, however, appears not to have been previously reported. You can find a whole gallery of images and videos of the behaviours we observed here, including some attacks on sleeping bees and wasps that we just happened to witness, and some that we set up.

Here’s an action shot of a candy-striped spider in the process of trapping a pair of still-sleepy sand wasps.

There’s much more in the paper about the diet of these spiders, and the details of how we studied them, and I hope you’ll go check it out! As for conclusions, this research resulted in a lot more questions than answers. What prompts the decision by these spiders to leave their webs and go marauding? (Presumably it is risky to leave the protection of the tangle web.) Do they all do it, or is this a new or learned behaviour in an environment where sleeping insects are particularly abundant? Do the spiders just search randomly for sleeping prey, or are they able to detect them from a distance (perhaps using chemical cues)? And what is the impact of all this predation on insect communities, particularly in threatened ecosystems like the sand dunes where we worked? These spiders take a lot of pollinators, but they also take all kinds of other bugs—are they impacting pollinator populations, helping to control insect pests in agricultural ecosystems, or both? The list goes on, and we have years of work ahead of us to find out!

Candy-striped spider wrapping a Coelioxys.

Speaking of which, if you’re in North America, YOU can help us with our ongoing work on candy-striped spiders! Please keep your eye out for these spiders, wherever you are, and contribute observations to our iNaturalist project. More information about this participatory research here.

*As far as I can tell, the “queen” alien from the movie has 6 limbs, but apparently James Cameron drew some inspiration from black widows in coming up with her morphology!

The global spread of misinformation on spiders

This post is a summary of a recently-published paper (and related open-access dataset) that was a very fun collaboration led by Stefano Mammola, Angela Chuang, Jagoba Malumbres-Olarte and 61 other arachnologist colleagues* from around the world.

Illustration of a person holding a medaphone and a newspaper with the headline "panic!!" He is standing on top of a map of the world, and a woman with an afro, wearing a white lab coat, and holding a spider biology textbook is correcting a misleading image on the newspaper with a red pen. White figures around the works are reading the news.
Summary illustration of the paper by coauthor Jagoba Malumbres-Olarte.

This study was largely motivated by our collective frustration at the often inaccurate and sensational way that spiders are portrayed in the media. But just how bad is the quality of reporting on spiders, and why is it so pervasive?

To answer these questions and understand how misinformation about spiders flows at the global scale, we amassed a team of experts from all over the world to analyze 10 years of online news stories about human-spider encounters. We first searched Google News (using variations on the search term “spider AND bite”) to find more than 5000 news articles from 81 countries published in 40 languages. We then read each paper to collect data including the date and location of each reported event, whether the story described a human-spider encounter (but not a biting event) or a “bite” or “deadly bite” (spoiler: articles rarely included evidence of an actual spider bite), and checked each news item for errors (e.g., misidentified spiders in photos, incorrect information about spider biology or venom) and sensationalism (somewhat subjective**, but often based on the inclusion of words like “horror”, “terrifying”, and “deadly” ). We also recorded whether the article quoted an expert, and whether they were a medical professional, a spider expert (usually an arachnologist or entomologist), or “other” (e.g., a pest management professional). All of this data, detailed methods, and a summary of what we found broken down by continent is freely available online here.

A large spider clings to a tree above floodwaters. Caption: The massive spider rescued from the Queensland flood seemed too horrifying to be real. Additional text below photo reads: It really does sound like something from a horror movie: a giant spider larger than a man's hand, which makes loud hissing sounds and has powerful long venomous fangs.
An example of sensationalist reporting on a human-spider encounter in Australia.

Overall, the quality of the reporting was poor: 47% of all articles contained one or more errors and 43% were sensationalist. Stories with photos of spiders or alleged bites were more likely to be sensationalized, as were stories that contained errors. Whereas quotes from medical or other experts were unrelated to sensationalism, stories that contained quotes from spider experts were much LESS likely to be sensationalized.

Drivers of sensationalism in media articles about spiders. Odds ratios to the left (right) of the dotted line indicate a decrease (increase) in the likelihood of sensationalism. Figure from Mammola et al. 2022.

One of our plans for the future is to create a global database of arachnological experts to make it easier for journalists to identify and contact arachnologists in their region who are willing to be interviewed and provide factual information about spiders. We are also already working on a paper outlining guidelines for journalists covering spider news stories, which we hope will help to prevent some of the most common errors we saw and improve the overall quality of reporting.

We next conducted an analysis to describe the flow of spider news stories around the world and to get at what may be driving the spread of (mis)information about spiders online. Unsurprisingly, countries with shared languages and with higher proportions of internet users were more likely to be connected in the global network. The number of medically important spider species present (i.e., those capable of harming and potentially killing humans) also increased the connectedness of individual countries within the network. Most notably, we identified sensationalism as a key factor underlying the spread of (mis)information.

Global distribution of news articles about on human-spider encounters showing links between countries (pies; n = 79) with each spider-related event reported by the press (dots, n = 2,644). The size of each pie chart represents the number of news articles published in the country between 2010 and 2020. Figure from Mammola et al. 2022

This study provides insight into what drives the global flow of information about spiders in particular, but can also teach us some more general lessons. Our results make us optimistic because they suggest a way to improve reporting on spiders, and in turn, to shift the quality and spread of online information more broadly. News stories are less sensationalized when they consult appropriate experts, and reducing sensationalism can help decrease spread of misinformation. We found that even local-scale events published by regional news outlets can quickly become broadcast internationally, which means improving news quality at the local scale can have positive effects that travel through the global network.

*Full author list: Stefano Mammola, Jagoba Malumbres-Olarte, Ingi Agnarsson, Valeria Arabesky, Diego Alejandro Barrales-Alcalá, Aimee Lynn Barrion-Dupo, Marco Antonio Benamú, Tharina Bird, Maria Bogolomova, Pedro Cardoso, Maria Chatzaki, Ren-Chung Cheng, Tien-Ai Chu, Naufal Urfi Dhiya’ulhaq, André-Philippe Drapeau Picard, Hisham K. El-Hennawy, Mert Elverici, Caroline S. Fukushima, Zeana Ganem, Efrat Gavish-Regev, Naledi Gonnye, Axel Hacala, Charles Haddad, Thomas Hesselberg, Tammy Ai Tian Ho, Thanakorn Into, Marco Isaia, Dharmaraj Jayaraman, Nanguei Karuaera, Rajashree Khalap, Kiran Khalap, Dongyoung Kim, Tuuli Korhonen, Simona Kralj-Fišer, Heidi Land, Shou-Wang Li, Sarah Loboda, Elizabeth Lowe, Yael Lubin, Marija Miličić, Alejandro Martínez, Zingisile Mbo, Grace Mwende Kioko, Veronica Nanni, Daniel Nwankwo, Yusoff Norma-Rashid, Christina Painting, Aleck Pang, Paolo Pantini, Martina Pavlek, Richard Pearce, Booppa Petcharad, Julien Pétillon, Onjaherizo Christian Raberahona, Joni A. Saarinen, Laura Segura-Hernández, Lenka Sentenská, Gabriele Uhl, Leilani Walker, Charles M. Warui, Konrad Wiśniewski, Alireza Zamani, Angela Chuang, Catherine Scott.

**For the news in English, Spanish, French, and Italian we checked to see how closely scores aligned for different collaborators assessing the same article, and we were pretty consistent.

Risky business: brown widow males choose cannibalistic adults over safer subadult females

I am very happy to share the publication of a new paper reporting research led by my fantastic colleague Lenka Sentenska and coauthored by Pierick Mouginot and Maydianne Andrade, in the journal Behavioral Ecology.

Brown widow spiders (Latrodectus geometricus), like their relatives the Australian redbacks (L. hasselti), are sexually cannibalistic. This is not the situation most people imagine when they hear “black widow,” however, in which the female devours the male after mating. In redbacks and brown widows, sexual cannibalism is better thought of as male self-sacrifice. The diminutive male somersaults during copulation and puts his abdomen in front of the female’s mouthparts, literally offering himself to her and continuing to transfer sperm as she begins to feed on him.

A copulating Australian redback spider pair. The much smaller male has somersaulted, presenting his abdomen to the female so that she can begin feeding on him. Photo: Sean McCann.

At first glance, this doesn’t seem like a particularly good outcome for the male. Although he is able to pass on his genetic material before his death (win!), he will be unable to mate with additional females and increase the total number of offspring he fathers. Recently, a group of colleagues discovered that male redbacks and brown widows can take a shortcut that allows them to survive mating. It turns out that just before their moult to maturity, immature females have fully developed reproductive organs ready to go under the cuticle that they are preparing to shed. This means that a male can bite through the cuticle and successfully copulate with a subadult female, and she will retain the sperm through her moult, and then go on to lay fertilized eggs once she is an adult.

This immature mating tactic has several major benefits for the male: he barely has to spend any time or energy courting the female (usually males court adult females for hours), males mating with subadults are more likely to copulate twice (thus depositing sperm in both of the female’s paired sperm storage organs), and subadult matings do not end in ritual cannibalism! On top of all that, females mated as subadults produce just as many offspring as those mated as adults. Given all this, you might expect that a male brown widow with a choice between an adult and a subadult female mating partner would choose the safer option: the subadult.

Previous studies (including this one by my colleague Dr. Sentenska) have tested this idea and found that when given a choice, brown widow males preferentially approach adults over subadults. This could just be because subadults are more difficult to detect from a distance; once they mature, adult female widow spiders produce a silk-bound sex pheromone that advertises their location and receptivity to males, and as far as we know, subadults do not produce such airborne signals. In this study, we wanted to see if males would make the same choices based on direct contact with silk (which may contain chemical information that allows males to discriminate between subadults and adults). We also wanted to find out what is driving the reduced courtship and copulatory cannibalism when males mate with subadult females—are courtship behaviours triggered by the sex pheromones on adult females’ webs, or do males adjust their behaviours depending on the kind of female they are attempting to mate, regardless of chemical cues on her web?

To answer these questions, we ran two experiments. First, we asked males if they preferred silk produced by adult or subadult female’s in a two-choice Y-maze. When the male entered the maze (via the common arm in the figure below) he would be walking on both kinds of silk, and then at the intersection of the Y he could choose to follow the adult or subadult silk trail. Once he got to the end of that arm, he could turn around and go investigate the other option, or continue searching on the first arm he chose. We found that initially, males were equally likely to choose each of the two arms of the Y-maze (not displaying a preference for either kind of silk), but that they spent more time on the adult silk. This reinforces the idea that males prefer adult females to subadult females based on silk-bound chemical cues (which spiders detect with hairs on their legs and mouthparts).

The y-maze setup for testing male brown widows’ responses to contact with dragline silk produced by adult or subadult females.

Next, we ran a web-swap experiment where we placed adult and subadult females on webs built by different individuals who were either the same stage or opposite stage, resulting in four combinations: subadults on subadult webs, subadults on adult webs, adults on subadult webs, and adults on adult webs. We then introduced a male onto each web and recorded his courtship behaviour, whether he successfully copulated, and whether he engaged in self-sacrifice behaviour (somersaulting and presenting his abdomen to the female).

This experiment revealed that the kind of web was the main driver of an important male courtship behaviour, silk laying (part of web reduction) and of the total time the male spent courting on the web at a distance from the female. The majority of males engaged in silk laying on adult webs, and almost no males engaged in this behaviour on subadult webs, regardless of whether the female on the web was an adult or a subadult. Males also approached females much more rapidly when they were courting on subadult webs, no matter the actual status of the female on the web. These results are consistent with the idea that males invest more time into courting adult females, and that energetically costly courtship behaviours like silk laying are triggered by the sex pheromone on silk produced by adult females.

The stage of the female herself, however, determined whether males successfully mounted and copulated with females, and how long it took them to progress from one stage of mating to the next. Males were much more likely to mount adult females than subadults, and were able to mount them more quickly. Similarly, males were more likely to copulate with adults than subadults, but the time they spent engaged in courtship on the female’s body prior to copulation was much longer for adult females. This is related to the result that males much more rarely engaged in mate-binding behaviour (wrapping the female’s body with silk) when courting subadult females compared to adult females. Intriguingly, we also found that males who bound females were more likely to successfully mount, particularly when the female was a subadult. This supports the idea that mate binding functions to increase female receptivity, perhaps via a pheromone on the male’s silk.

The tiny brown widow male in this photo has reduced much of the larger female’s web, leaving a thick rope of silk that she is hanging from. Here he is laying silk on her front legs, part of the “bridal veil” or mate-binding behaviour. Photo: Sean McCann.

Finally, we found that males nearly always somersaulted during copulation with adult females, but almost never offered themselves to subadults. This indicates that the lack of sexual cannibalism during subadult mating is a result of males choosing not to engage in self-sacrifice, rather than adult females being more cannibalistic than subadults, which suggests that perhaps we should change our thinking about subadult females being the “safer” option for males.

Here the male is withdrawing his coiled embolus (one of his paired sperm-transfer organs) from the female’s genitalia. The drop of fluid on his abdomen indicates that the female bit him after he somersaulted during the first copulation. He can now copulate a second time, and again offer himself to the female so that she can complete her meal. Photo: Sean McCann

Taken together, our results confirm that male brown widows prefer to approach and attempt to mate with adults than subadults, despite the apparent advantages of subadult mating. The shortened time to mating and the lack of cannibalism, however, may be better thought of as males investing less into mating with subadults than as benefits of this tactic. This makes sense when we consider that adult females seem to be more receptive to male mating attempts than subadults, and that they are ready to produce an egg sac shortly after copulation, whereas subadults must first moult to maturity. Moulting spiders are extremely vulnerable to predators, and all the advantages of mating with a subadult disappear if she dies before producing any offspring. We conclude that mating with adults, despite resulting in a male’s death, may actually be the safer option in terms of the return (offspring) on his investment into a given female.

References & related reading:

Sentenská, L., Neumann, A., Lubin, Y., & Uhl, G. (2021) Functional morphology of immature mating in a widow spider. Frontiers in Zoology 18: 1-18.
Sentenská, L., Uhl, G., & Lubin, Y. (2020) Alternative mating tactics in a cannibalistic widow spider: do males prefer the safer option?Animal Behaviour 160: 53-59.
Biaggio, M. D., Sandomirsky, I., Lubin, Y., Harari, A. R., & Andrade, M.C.B. (2016) Copulation with immature females increases male fitness in cannibalistic widow spiders. Biology Letters 12: 20160516.

Entomology bandana fundraiser

UPDATED (18 Nov 2021) with new bandana design & corrected species list!

The Student and Early Professional Affairs Committee of the Entomological Society of Canada is selling bandanas to raise money for its Annual Scholarship Fund, which supports entomology graduate students working at Canadian universities.This 100% cotton bandana, available in red or charcoal gray, is printed with the logo insects* of the ESC and all of the regional entomological societies, plus a bonus arctic wolf spider to represent the northern territories. The beautiful art was created especially for the ESC by Mary Capaldi, and you can find more of their fabulous work, much of it entomology-themed, here.

You can pre-order bandanas on Etsy now, or by contacting me by email or on twitter (if you live in Montreal, we can avoid the shipping costs). We anticipate that the bandanas will be available for shipping around the time of the 2021 ESC JAM in November, in plenty of time for holiday gift-giving. This is the perfect fieldwork accessory for you or the arthropod enthusiast in your life!

*featured taxa:

ESC – Grylloblatta campodeiformis

ESBC – Boreus elegans

ESAb – Chortophaga viridifasciata Apamea devastator

ESS – Melanoplus bivittatus

ESM – Cicindela formosa generosa

ESO – Danaus plexippus

SEQ – Limenitis arthemis arthemis

AES – Rhagoletis pomonella

Arctic wolf spider – Pardosa glacialis

AAS 2021 Virtual Meeting: an invitation to all arachnophiles!

The American Arachnological Society is hosting a Virtual Conference Thursday June 24 – Thursday July 1. A keynote talk by Maydianne Andrade will open the meeting on the evening of the 24th. Program highlights include plenary talks by Mercedes Burns, Lauren Esposito, and Ivan Magalhães; oral and poster presentations; and a panel discussion and workshop on actions to dismantle racism and promote equity, diversity, and inclusion in arachnology.

All arachnologists and arachnid enthusiasts are invited, and there is still time to register (only 20 USD) for the meeting and the associated events before the deadline, which is Monday June 14. Don’t miss this chance to participate in workshops on arachnid photography, collecting, and more, two movie nights (featuring Maratus and Sixteen Legs), a photography and art contest, and a virtual arachnid bioblitz!

Freely accessible & family-friendly events include a public talk about arachnids by Jillian Cowles, author of Amazing Arachnids (this talk will be livestreamed on youtube on Sunday June 27) and an Arachnid Q&A livestream with Isa Betancourt, host of The Bugscope (Saturday June 26).

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).


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.