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The Fine Art of Herding Spiders

Your house has its own ecosystem, and you’re just a side character in it. Don’t believe me? Look closer.

A close-up of one of my newest neighbors

I’ve been wrangling newborn animals in my house this week. My tools: a Ball jar, a kid’s paintbrush, and my 20/20 vision. When I find one rambling around my ceiling or wall, I sneak up and carefully place the jar underneath it. Then, with a careful touch of the paintbrush, I flick it in.

Obviously I’m not talking about baby lambs or chicks or even mice. If you know anything about me, you can probably guess where this is going: My house is full of baby spiders.

We as a culture have a tendency to draw a bright line between human space and natural space. Outside, there’s grass and trees and all the things that live in them, clashing and evolving according to their logic. Inside is our space, sterile and orderly and under human control. But you only have to give it cursory thought to realize how false that is. Carpenter bees drill into our siding, weeds sprout from cracks in the concrete, ants cart off the crumbs we drop on the ground. And sometimes, in some quiet corner of the house, a spider weaves an egg sac.

While we’re conditioned to think of them as invaders, most, of the spiders you find in your home have lived their whole lives there. Synanthropic species like the long-legged cellar spider Pholcus phalangioides or the noble false widow Steatoda nobilis thrive in the warmer, quieter nooks of human houses. They’re a cog in the machinery of your house’s ecosystem, preying on houseflies, gnats, and occasionally each other and, when they get a chance, making babies to continue the cycle.

The babies I’ve been corralling this week are yellow sac spiders from the genus Cheiracanthium. Specifically, they’re either native black-footed yellow sac spiders (C. inclusum) or introduced northern yellow sac spiders (C. mildei)—both are common, and even in adults, it’s hard to impossible to tell the difference without putting them under a microscope. About the size of a quarter when full-grown, these creamy yellow-white spiders are the most common species I find in my house: From fall through spring, almost every spider I catch is a yellow sac spider.

A full-grown Cheiracanthium

As common as they are, yellow sacs are probably some of the most maligned spiders in the United States. Google them, and you’ll be treated to a litany of pest control websites, “fact sheets,” and even medical journal articles claiming that their bite is necrotic, causing tissue and skin around the wound to die and slough off and leaving huge scars in their wake. If you’re anxious after learning that fact, you’re not alone.

The problem? There’s actually no credible evidence it’s true. Just ask Richard Vetter: A retired research scientist from University of California-Riverside who specializes in brown recluses, Vetter knows a thing or two about both necrosis and arachnophobia: In 2020 he won an Ig Nobel prize for an article in American Entomologist which found that a significant portion of professional entomologists were still afraid of spiders.

In a 2006 article in the American Journal of Tropical Medicine and Hygiene, Vetter and his coauthors analyzed records of 20 verified yellow sac spider bites in the US and Australia and found none of them resulted in necrotic lesions. When they expanded their search to Europe, the results were more or less the same: Out of 39 confirmed bites, only one—caused by a species that doesn’t live in the U.S.—could be credibly linked to a very mild case of necrosis. In the paper, Vetter and his coauthors called the spiders “virtually innocuous” and suggested that speculative case studies and doctors misdiagnosing wounds could have contributed to the public’s misplaced fear of Cheiracanthium.

That’s great for me, because my house is lousy with them. And while I try to catch and relocate yellow sac spiders outside, I appreciate the free pest control they provide, and love to watch them take down lacewings and moths under my porch light. The babies I’m catching on my ceiling now look exactly like shrunk-down versions of their parents: an arrow-shaped abdomen and a creamy-yellow cephalothorax, all small enough to balance on the pointy end of a pin.

In spring, I caught two adult yellow sac spiders on my living room wall, a courting pair. The female crouched in place, her legs bent close to her body; the male twitched his palps as he slowly crept closer, probably wary of the chance that she could turn him into her next meal. Once you’ve seen that full circle, from pair to egg sac to sling and back again, it’s hard to hate them: they’ve been living their lives in this house for generations, since long before I moved in. So I’ll keep gently sweeping them into a jar with my paintbrush and taking them outside, where I’ll watch them scatter across the front step, spiderlings about to step into their own life cycle.