Pill bugs (roly polies)


The endearing roly poly brings back memories from our childhood. We know them as harmless creatures, rolling up into tight little balls when handled. Their group names, Armadillidiidae and Armadillidae, were clearly inspired by the way armadillos roll up to protect themselves. Their topside is heavily armored to protect against predators, and balling up serves as a way to protect their soft underside from attack.

Roly polies belong to a broad group called the woodlice. There are many species of woodlice, and many look very similar, but only a few can roll up into perfect spheres. The roly poly you probably played with was Armadillidium vulgare, the common pill bug.

There is a spider called the woodlouse hunter that feeds on roly polies and their relatives. The spider’s inordinately long fangs can reach around the hardened plates and pierce the underside of their prey. Despite their specialized fangs, these spiders will feed on any small creature they can overpower, not just roly polies. Although fearsome in appearance, these spiders are harmless to humans and are very rarely seen inside buildings.

People think that roly polies are insects or millipedes. I was convinced, as a child, that roly polies were stumpy millipedes. They are not, despite the resemblance. Roly polies are actually crustaceans. They are more closely related to lobsters, crabs, and shrimp than to millipedes, spiders, or insects.

Having crustacean ancestry means that they are limited to and primarily found in damp areas. You can expect to find them in mulch, under rotten logs, and beneath stepping stones. They are scavengers on decaying organic matter and can be found in proximity to millipedes and springtails (other moisture-loving critters with similar diets). Roly polies are generally considered to be beneficial. Their activities produce compost and turn the soil. Occasionally, they can be pests of the garden by feeding on seedlings and ripening fruit.

Roly polies can annoy people by getting inside structures. If conditions become very dry, they migrate in search of moisture to prevent from desiccating. They can invade homes by the dozens, or by the hundreds, in pursuit of wetter habitat. Although their presence is unwanted, they do not bite, spread disease, or damage wood or property. Roly polies that wander inside will die because homes are far too dry for them. Roly polies (and millipedes) are indicative of high moisture around the home, like overwatered mulch beds.

Crabs are delectable, shrimp are scrumptious, and lobsters are an expensive delicacy. Logic might dictate that roly polies should also taste pretty good. Before you go out to collect a bucket of roly polies, consider these words from Paul Harding, a British isopodologist. “If you accidentally get one in your mouth, it’s a most unpleasant experience. Basically, it tastes of strong urine.”