Count the legs of a woodlouse and you'll know they're not insects or spiders—or even millipedes.  Juvenile and adult woodlice have seven pairs of legs on their many-segmented bodies.  (Insects have six pairs of legs, spiders have four pairs.)

Woodlice are land-going crustaceans.  As you might expect from terrestrial relatives of crab and shrimp, keeping moist is a high priority for woodlice.

Lacking the heavy, waxy, water-retaining surface of other land arthropods, woodlice seek cool, dark, and damp locations.  They take up precious water several ways:  by sipping water through the mouth, through the food eaten, and by using the small tubes at the tail end to draw water into the anus.

All animals (even marine crustaceans) require oxygen.  Many species of woodlice draw their oxygen from moist air using lung-like structures on the underside, near the tail.  Look for light-colored spots, protected from drying by flaps.

Like other arthropods, from crabs to spiders, woodlice must molt to grow.  Adult woodlice molt about every two months, shedding the exoskeleton on the back half of the body a few days before shedding the front half, leaving the animal bi-colored for a short time.  Why don't we see more shed skins?  The frail cast exoskeletons are often eaten by their producer or by other woodlice.

Although such small animals may seem to live fast-paced lives, some larger species of woodlice don't breed until they're two years old.  They're surprisingly maternal, too:  Pale, newly hatched woodlice spend the first couple of weeks of their lives tucked away in a special, damp pouch on the underside of the mother.

Woodlice feed primarily on dead and decaying material they encounter as they travel through leaf litter and other hidden places.  Occasionally, they turn to tender living plant material when their populations get crowded.  Woodlice process bits of dead plants and animals into nutrients more readily used by the plants in your garden ecosystem.  In turn, woodlice are eaten by shrews, salamanders and newts, frogs, lizards, some spiders and small birds.

While Oregon has at least one native woodlouse (Ligidium gracile), the ones most commonly found in our gardens and basements, such as the sowbug and pillbug, are introduced from Europe.

If you've ever accidentally squashed a handful of woodlice, you may have noticed the smell of ammonia.  Woodlice don't process their nitrogen-based waste into urea (which we excrete as urine), but pass the gaseous ammonia off through their thin shells.

Woodlice don't bite and don't damage our buildings or possessions.  In fact, in their native Great Britain, our garden woodlice are sometimes kept as pets.

These fascinating land-living crustaceans are much more fun to watch than squash.

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Visit our pages on related topics:  

Dungeness crab

spiders

salamanders

frogs

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Wavecrest Discoveries can craft your personal discovery of this delightful part of our world by customizing one of our distinctive guided excursions.   Our walks, tours, and special activities are wonderful ways to explore this fascinating region—and are the perfect entertainment for guests.