yellow sac spider | spiderbytes

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.

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

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Meet the spiders in your house with Travis McEnery!

Yellow sac spiders (family Cheiracanthiidae)

Myth-busting