Wild Side: The long-bodied cellar spider

Probably the easiest arthropod to find in midwinter.

The long-bodied cellar spider, Pholcus phalangioides. — Matt Pelikan

I feel like part of my job as a nature columnist is to serve as a public relations consultant for animals that are unfairly maligned. Today’s client? The long-bodied cellar spider, Pholcus phalangioides.

These things are, let’s admit, a bit creepy both in appearance and in habits. With a body length ranging up to nearly half an inch, they’re good-size spiders to start with. But the salient trait of this species is a set of outrageously long, thin legs: On a large female, the span of those threadlike limbs may approach three inches.

Many people are misguided enough to find spiders of any sort to be repulsive, and the exaggerated anatomy of a cellar spider seems to make this species especially reviled. The cellar spider’s habits don’t help much: As their common name suggests, they’re animals of dark, damp places, building their untidy webs in corners or between rafters in cellars, attics, or closets. It’s not a charismatic lifestyle.

Pholcus is sometimes referred to with the common name “daddy longlegs,” which highlights why serious students of spiders avoid common names altogether in favor of more precise, if sometimes awkward, scientific names. “Daddy longlegs” is also a name applied to the Opiliones, a superficially similar group that is only distantly related to the cellar spider.

Also called harvestmen, Opiliones share the delicate legs of Pholcus. But the body segments on a harvestman are merged into a single, nearly round object, while a true cellar spider has a more elongated body with a distinct division between the abdomen and the forward sections.

The worst slander perpetrated against Pholcus phalangioides is that these spiders are highly venomous, and that only the shortness of their fangs prevent them from being dangerous to humans. Fake news! The venom turns out to be not especially potent even to the arthropods that are a cellar spider’s usual prey. And the fangs of this spider, at least on large individuals, actually are long enough and strong enough to pierce human skin (not that these spiders have any interest in doing so).

But the weak venom renders this species harmless. On the rare occasions when they do bite humans, the effects are said be a trivial and short-lived sting. As is true of all spiders, actually biting something the size of a human is an absolute last resort for a cellar spider: You’d need to try quite hard to get one of these things to put its fangs into you.

The actual defensive strategy of a cellar spider is less dramatic but more interesting. When one is disturbed in its web, the spider shakes the strands of the web, setting the whole shebang into motion and turning the spider itself into a bobbing target for any would-be predator. You can demonstrate this for yourself by giving a good poke to an occupied cellar spider web; most of the time, the spider is instantly swinging.

While the origin of this species apparently lies in the Mediterranean region, cellar spiders have been transported widely if accidentally during the course of human commerce and migrations, and now occur quite widely around the world. Even under natural conditions, Pholcus prefers to live in cavelike settings. And the species is not cold-hardy. So the cellar spider truly does live up to its name, being rarely found outside human structures. But in an artificially heated environment, cellar spiders are active year-round, and are probably the easiest arthropod for a Vineyard-based bug enthusiast to find in midwinter.

Perhaps the most surprising trait of the cellar spider is its longevity. Depending on their environment and food supply, it may take months or even a full year for one to reach maturity, passing through, typically, a half-dozen molts as it grows. And an individual may reportedly live as long as three years altogether if not eaten by something, or mashed by a misguided human.

A female, which is larger than a male and equipped with a larger abdomen, typically lays a few dozen eggs at a time, wrapping them loosely in silk and then holding the package in her jaws while resting in her web.

Predatory like all spiders, Pholcus is not particular about its prey, and hence lives mainly on whatever other invertebrates blunder most regularly into its web. Crane flies seem to be a frequent victim in our basement, along with mosquitoes and other spiders. In hard times, cellar spiders have no objection to eating each other, and I suspect that cannibalism routinely reduces the number of young cellar spiders after they hatch.

All in all, I guess I can understand how people find cellar spiders off-putting. But the worst you can fairly accuse these arthropods of is the construction of untidy webs that accumulate in corners over time. They pose no risk to you or to your pets, and if anything, their overall effect is beneficial, as they deftly prey on other invertebrates that have made their way into your home. Leave them alone, or better yet, make the effort to get better acquainted.