So common that they are easily overlooked, pill bugs (Armadillidium vulgare) are very numerous in our yard. These creatures are not insects but crustaceans: terrestrial isopods. One other species of isopod is also found here and is called the sow bug. These differ from pill bugs in being flatter, faster, having a longer tail, needing more moisture, and not being able to roll up in a ball. Pill bugs are also called pill woodlice and roly-polies.
Being related to aquatic crustaceans, pill bugs have gills that must be kept damp. Their hard exoskeletons do an admirable job of reducing moisture loss, and pill bugs can be seen crawling around in all but the very driest conditions. They will drown if submerged in water. Pill bugs are scavengers that eat just about anything, including dead vegetation, tender seedlings, animal droppings, and the leather on shoes.
Pill bugs are native to Europe and were introduced to the U.S. where they are now widespread. They are most frequently found under rocks, in compost piles, and in well-watered lawns.