Meet the spiders in your house with Travis McEnery!

Posted on June 19, 2023 by cataranea

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 s laps.

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.

Announcing a new project: Recluse or Not?

Posted on October 10, 2017 by cataranea

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.

Yellow sac spiders (family Cheiracanthiidae)

Posted on June 19, 2016 by cataranea

Note: this post has been updated to reflect that the yellow sac spiders are now in the family Cheiracanthiidae. At the time of first writing, they were in the 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 Cheiracanthiidae).

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.

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.

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

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

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.

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

How to tell if a spider is not a brown recluse

Posted on June 8, 2015 by cataranea

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UPDATE (Oct. 2017): We have just launched a new community science and public education initiative called Recluse or Not? This is a collaboration with Eleanor Spicer Rice and Matt Bertone that will allow us to obtain information about where people are finding recluse spiders inside and outside their native range in North America and help people to learn more about recluse spiders and how to identify them. Please check out the project page here for more details, and send us your photos of suspected recluse spiders on twitter! If you are not on twitter, please feel free to email me (you can find my contact information on the “about me” page).

This post addresses one of the most common spider identification questions in North America (north of Mexico): is it a brown recluse?*

A female brown recluse, Loxosceles reclusa. Photo: Alex Wild, used with permission.

The brown recluse spider (Loxosceles reclusa) is arguably the most feared and most misunderstood spider species in North America. So, here we will find out how to tell if a spider is not a brown recluse. But before we do, it’s important to note that even if you do find a brown recluse, it’s not that big a deal.

Arachnologist Rick Vetter is an expert on the brown recluse spider who has done a ton of research on where they are (and aren’t) and how dangerous they really are (hint: not as dangerous as you think), as well as spending a lot of time dispelling myths and misconceptions held by both the public and the medical community. His website is full of excellent resources, and is the source of most of the information here. I encourage you to peruse his website and the articles linked in this post yourself, but I will highlight a few of the more compelling reasons that the brown recluse hysteria is unwarranted.

Exhibit A: brown recluse bites are rare even where the spiders are abundant.

A family lived in a house full of brown recluses (more than 2000 of them!) for half a year and not a single bite occurred. Even in places where brown recluses are common, bites are very rare. Of those rare bites the vast majority of bites can be effectively treated with RICE (rest, ice, compression, and elevation) without any dire consequences. The small percentage of bites that are very serious are the ones that get all the attention in both the medical literature and the media, which has led to the misconception that recluse bites are always severe, require hospitalization, result in extensive scarring, and so on. Furthermore, misdiagnoses of all manner of other (more serious) conditions as brown recluse bites are rampant throughout North America (even in areas where the spiders do not occur), adding fuel to the already raging fire.

Now that all that’s out of the way, here is a series of questions to determine if a spider is NOT a brown recluse**. (Some of these may seem silly, but many of the spiders below that are not brown recluses are regularly misidentified as brown recluses by non-experts. Many people aren’t aware just how many different kinds of spiders there are, and for some, seeing brown, any marking vaguely reminiscent of a violin, and 8 legs is enough to conclude that a creature as a brown recluse.)

For those who want to skip the fine print, if the answer to question 1a or 1b is “yes”, it’s probably not a brown recluse. If the answer to any one of the remaining questions is “yes”, it’s definitely not a brown recluse.

1a. Are you in Canada (or Alaska)?

The range of the brown recluse spider does not extend into Canada. If you are in Canada, you are extremely unlikely to encounter a brown recluse spider. (Also see notes under 1b.)

1b. Are you in a state outside of the range of the brown recluse?

Above is a map of the known ranges of all of the species in the genus Loxosceles in North America. If you are anywhere outside the red-outlined region, you are very unlikely to encounter a brown recluse.

[update 2021] Below is an updated range map based on the latest data, made by Matt Bertone. For more information about recluse spiders, check out our Recluse or Not? page.

Brown recluses are occasionally found outside this range – sometimes they hitch a ride with people moving around the country (in boxes that have been stored in basements, for example). But even in these cases they will typically remain in the building into which they are introduced because they are very poor dispersers. Just because one or a few brown recluse spiders have been found in a new area does not mean that their range has expanded or that they are abundant there. (Note: A brown recluse spider bite diagnosis in an area outside their range does NOT mean that brown recluse spiders have been found there. Many doctors erroneously diagnose spider bites in the absence of any evidence, namely a spider that has been identified as the culprit.)

2. Is it on a web out in the open?

Some brown web-building spiders that are not brown recluses. Clockwise from top left: common garden spider (Araneus diadematus) on orb-web, dome-web spider male (Neriene radiata) false widow spider (Steatoda grossa) on cobweb giant house spider (Eratigena atrica) on funnel-shaped sheet web. Photos: Sean McCann.

If you find a brown spider on a web out in the open, it is not a brown recluse. Unlike the various brown web-building spiders shown above, each with their different types of web, brown recluse spiders do not use silk for prey capture. They do build small irregular silk retreats in which they hide during the day. These retreats are made low to the ground and out of sight in cracks and crevices or under objects like rocks.

Update (8/06/2015): I should mention that house spiders in the family Agelenidae are probably the most likely spiders to be mistaken for brown recluses in Canada. While females will usually be found on their webs, males are often found out and about when searching for females. They all look pretty similar to the one pictured below, but see this post for more information house spiders and hobo spiders.

Female giant house spider (Eratigena atrica – formerly Tegenaria duellica). These spiders are often mistaken for recluses, but note the pattern on the abdomen. Photo: Sean McCann.

3. Does it have stripy or spiky legs, or more than one colour on its abdomen?

Stripy legs + patterned abdomen = not a brown recluse. Photo: Sean McCann.

If you find a spider that has stripes or large spines on its legs, it is not a brown recluse. If it has a patterned abdomen, it is not a brown recluse.

Stripy legs with large spines + patterned abdomen = not a brown recluse. Photo: Sean McCann.

Brown recluses have plain brown abdomens and plain brown legs with fine hair but no large spines.

4. Does it have extremely long and skinny legs?

Cellar spider, Pholcus phalangiodes (family Pholcidae). The dark spot on the cephalothorax looks a bit like a violin, but do not be fooled. This is not a brown recluse. Photo: Sean McCann

If it has extremely long skinny legs like the spider in the image above, it is a cellar spider (or daddy-longlegs), not a brown recluse. Despite looking very dissimilar to brown recluses, these spiders are often mistaken for brown recluses because of the “violin” mark on the back. Having a violin-shaped marking is not, by itself, a good way to determine if a spider is a brown recluse.

4. Is it really big?

Brown recluses are not huge spiders. If its body length (not including legs) is more than 0.5 inches or about 1.25 cm, it’s definitely not a brown recluse.

5. Does it have 8 eyes?

This is the dead giveaway, provided you are close enough to the spider to count its eyes. If it has 8 eyes (like most spiders), it is not a brown recluse. Below are some 8-eyed spiders that are sometimes mistaken for brown recluses.

Fishing spider (family Pisauridae) actually a close relative of fishing spiders in the family Trechaleidae, with 8 eyes. Also see: stripy, spiky legs. Photo: Sean McCann.

A wolf spider (family Lycosidae). Wolf spiders have 8 eyes and spines on the legs. Photo: Sean McCann.

A sac spider (family Clubionidae) A ground spider (family Gnaphosidae, genus Drassodes). It looks a bit like a brown recluse, but again, has 8 eyes, some larger spines on the legs, and a dark stripe on the abdomen. Photo: Sean McCann.

Huntsman spider (family Sparassidae). These spiders are fairly frequently mistaken for brown recluses. Note the 8 eyes in 2 rows, and spines and darker dots on the legs and abdomen. Photo: Sean McCann.

Update (12/06/2015): Another 8-eyed spider that can easily be mistaken for a brown recluse (and is common in the southern states) is the male southern house spider. It has a similar violin-like marking on the back, but several other features that distinguish it from brown recluses. The 8 eyes are all tightly clumped together, it has conspicuous spines on the legs, and its pedipalps (the two small leg-like appendages at the very front end of the spider) are extremely long and stick straight out in front of its face (compare to a male brown recluse spider here).

Male southern house spider (Kukulcania hibernalis). Photo: Sam Heck, licensed under CC BY-NC 2.0.

Some other spiders that are not brown recluses, like the woodlouse hunter Dysdera crocata, also only have only 6 eyes, but they are arranged differently (not to mention D. crocata is red or pinkish or orangish in colour, not brown).

Female woodlouse hunter, Dysdera crocata. Her 6 eyes are all in a tight bunch in the centre of the cephalothorax, and her massive fangs are much larger than those of a brown recluse. Also, these spiders are not brown. Photo: Sean McCann.

Brown recluses only have 6 eyes, arranged in 3 pairs.

This is a brown recluse. It has only six eyes. Also note the fine hairs on the legs, but no spines, and the plain brown abdomen. Photo: Alex Wild, used with permission.

If you answered no to all those questions (or all but questions 1a and 1b and you’re really lucky!) AND the spider looks just like the one in the image above, then you’ve found a brown recluse. If not, then it’s another kind of spider that is totally harmless. (The only other medically significant spiders in North America are black widows). Either way, please remain calm. Spiders are not out to get you, and will leave you alone if you leave them alone. Here are some tips for avoiding brown recluse bites if you do live within their range. Still not sure about any of this? Please feel free to tweet at me (I’m @Cataranea on twitter) or comment here if you have any questions and I’ll be happy to try to answer them.

*I’ve also started answering this question on twitter with the hashtag #notabrownrecluse. This campaign, with the goal of educating people about the brown recluse spider, is ~~a blatant ripoff of~~ inspired by wildlife biologist David Steen (he’s @AlongsideWild on twitter), who tweets snake identifications using the hashtags #NotACottonmouth and #NotACopperhead. For more about his awesome twitter outreach, check out this excellent article: ‘This snake scientist is the best biologist on twitter‘.

**This guide is based on the following resources:

Vetter, Rick. (1999). Identifying and Misidentifying the Brown Recluse Spider. Dermatology Online Journal, 5(2). link

Vetter, Rick. (2009). How to Identify and Misidentify a Brown Recluse Spider. Web Resource. link

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

Posted on September 25, 2014 by cataranea

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

Misinformation about spider bites is everywhere

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

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

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

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

1. The hobo spider is not aggressive.

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

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

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

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

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

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

A female hobo spider. Photo by S. McCann.

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

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

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

Arachnologists Robb Bennett and Rick Vetter advise doctors that,

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

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

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

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

Did we mention that spiders hardly ever bite people?

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

A black widow, photographed by S. McCann.

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

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

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

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

What happens when you poke, prod and pinch black widow spiders? You might be surprised…

Posted on February 14, 2014 by cataranea

This post originally appeared on Chris Buddle’s blog Expiscor at Scilogs.com.

A stunning female western black widow (Photo: S. McCann)

People seem to have a particular fear mixed with fascination when it comes to venomous animals, and whenever I talk about my work with black widows I am invariably asked questions like, “have you been bitten yet?” The answer is, of course, no. Spiders almost never bite people. I’m always quick to relate that in my experience black widows are not aggressive, even when I go around poking and prodding them with my bare hands.

Replicated experimental results always carry more weight than anecdotes, however, so I am delighted to share this recent paper: Poke but don’t pinch: risk assessment and venom metering in the western black widow spider, Latrodectus hesperus.

Hey look!! An actual peer-reviewed research paper about the poking, prodding, and pinching of black widows, confirming that they are reluctant to bite, even when threatened. Not only that, but the study provides some cool data suggesting that these spiders are capable of assessing risks to make decisions about how to defend themselves.

Here are the details:

David Nelson and his coauthors wanted to know if black widows change their defensive behaviour depending on the level of threat they are faced with. To find out, they used gelatin ‘fingers’ to place spiders in three different threatening situations: a ‘low threat’ attack was a single poke with one finger, a ‘medium threat’ was a series of prods simulating a more persistent attacker, and the ‘high threat’ was three a series of long pinches of the spider’s entire body between two fingers, as might be experienced if being grasped by a predator.

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Figure 1 from Nelson et al. 2014

They found that the spiders engaged in several distinct defensive behaviours during these experimental attacks: retracting the legs toward the body, moving (often retreating), ‘silk-flicking’ (drawing sticky silk out of the spinnerets with last pair of legs and flinging it toward the attacking finger), ‘playing dead’ (curling up into a ball), and biting.

During low-threat, single pokes, no bites occurred. Most spiders were completely non-confrontational, simply moving away, and only rarely flicking silk. When the threat level escalated to persistent prodding, the spiders changed their defensive behaviour: roughly half of them flicked silk, some played dead, and only one spider (out of 43) attempted to bite the offending finger. Silk-flicking is much safer than biting for a black widow – she can maintain her distance while flinging sticky silk to subdue or slow down her attacker. Biting, on the other hand, requires getting up close and personal with the assailant in order to pierce it with her tiny fangs, making her much more vulnerable to injury.

See the red tips of this black widow’s puny fangs? It’s a lot safer for her to keep her distance in threatening situations than get close enough to use them (Photo: S. McCann)

Only when the spiders were being pinched between two fingers (with the mouthparts already positioned right up against their ‘attackers’) did biting start to become a more common, last-resort tactic: 60% of the spiders bit the fingers as a result of being squeezed for an extended period of time, delivering on average 2.7 bites each. Pinching also resulted in silk-flicking by about half of the spiders, and a few played dead.

This is all great information, but when the spiders did bite the gelatin fingers, there was no way of knowing how much venom they injected, if any at all (sometimes venomous animals deliver ‘dry’ bites). The next question the researchers wanted to answer was, do the spiders control whether and how much venom they inject when biting? In particular, they wanted to know if the amount of venom injected would vary depending on the type of threat (in this case either pinching a leg with forceps, or grasping the abdomen with gloved fingers).

For this experiment they came up with a clever method to collect the venom: a small vial with a thin membrane over the opening was presented as a target for the spiders to bite. If a spider did bite, her fangs would pierce the membrane (the number of holes would indicate how many times) and any venom she expelled would be collected in the vial so the volume could subsequently be measured.

It turned out that more than half of all bites were dry (no venom was detected in the vials). The black widows delivered more bites per target when they were pinched on a leg than on the abdomen, but more venom was released with each bite when the abdomen was pinched. Being grasped by the body is a high-risk situation for a black widow because her abdomen is unarmored and vulnerable; a strong squeeze or puncture can be deadly. Pinching a single leg, on the other hand, represents a non-life threatening attack. Spiders can autotomize (drop) their limbs and survive without significant ill effects.

The team also found evidence that the spiders delivered more venom per bite when repeated threats were spaced 5 minutes apart than 5 seconds apart. Attacks after the longer intervals might have been interpreted as coming from new assailants, each requiring a larger dose of venom than a second or third bite to the same persistent attacker.

The results all indicate that black widows have fine control over how much venom they inject when biting. First, they can decide whether or not to use venom at all. Some spiders gave dry bites, then wet bites, as well as vice versa, demonstrating that dry bites were not simply a result of running out of venom. Furthermore, they can vary the amount of venom they inject during individual bites and in response to different kinds of threats.

Both silk and venom are metabolically expensive to manufacture, so it makes sense that spiders would be selective about when and how much of these resources to deploy in defense. This study suggests that they are able to assess risks and adjust their responses accordingly, only dipping into their reserves of silk and venom as the threat level escalates towards a life-or-death situation.

What does this all mean for humans? Grabbing and pinching spiders is generally not a good idea – they might get injured and could bite defensively. This is just good sense and didn’t require a scientific study to confirm, but the new data suggest that even if a black widow does bite, she’s not necessarily going to inject any venom. It’s also important to note that in the experiments where bites did occur, the spiders always had a ‘finger’ or target placed in direct contact with their mouthparts.

An unaggressive female black widow takes a stroll across my hand. Although I never grab spiders to pick them up, coaxing them onto my hands and letting them wander around on their own steam has never been a problem. (Photo: S. McCann)

The most exciting thing this study tells us is that spiders can make decisions about how to respond to threats (which sometimes include humans) – further evidence of their incredible sophistication. Perhaps more importantly for the arachnophobic, it suggests that black widows would much rather conserve their valuable venom for use in dispatching their next meal than waste it on a human who is of no interest as prey!

Spiders in general are amazing creatures worthy of our admiration and respect. I hope that this new information about black widows might convince some that there is more about them to be fascinated by than to fear!

References and related reading:

Nelsen, D. R., Kelln, W., & Hayes, W. K. (2014). Poke but don’t pinch: risk assessment and venom metering in the western black widow spider, Latrodectus hesperus. Animal Behaviour, 89, 107-114. http://dx.doi.org/10.1016/j.anbehav.2013.12.019

Vetter, R. S. (1980). Defensive behavior of the black widow spider Latrodectus hesperus (Araneae: Theridiidae). Behavioral Ecology and Sociobiology, 7(3), 187-193. doi:10.1007/BF00299363

W. Cranshaw (2014). Western widow fact sheet: http://www.ext.colostate.edu/pubs/insect/05605.html

Getting friendly with widow spiders

Posted on December 5, 2013 by cataranea

For a lot of people, black widows inspire fear, but to me they are friends with amazing habits and shy, unaggressive* natures. Check out Chris Buddle’s post over on Expiscor for a conversation about these beautiful, misunderstood spiders!

Sean handles a juvenile black widow in the field (photo: Sean McCann)

Sean handles a juvenile western black widow. No, he did not get bitten! (photo: Sean McCann)

*In my experience, black widows are not aggressive towards humans. With potential prey (various arthropods including other spiders), of course, it’s an entirely different story!

spiderbytes

This is a blog about spiders (and other arachnids)

Category Archives: spider myth-busting