Pillbugs are arthropods in the subphylum Crustacea or crustaceans. They belong to the class Malacostraca or soft shell crustaceans and the order Isopoda. Pillbugs are more closely related to shrimp, crayfish, and lobsters than insects. Pillbugs are wingless and gray to black. They have seven pairs of legs, well-developed eyes, and are about 3/8-inch long when fully grown. When disturbed they often roll themselves into a ball.
Pillbugs are most active and mate mainly in the spring. To survive, isopods must remain in a moist habitat. In hot weather they remain in dark, damp areas such as cracks in the field or under crop residue during the day and become active at night. They overwinter as inactive adults. A female carries from seven to 200 eggs in a brood pouch on the underside of her body. Eggs hatch in three to seven weeks, and the young are white. The female carries the young in her brood pouch for six to eight weeks until they can care for themselves. There may be one or two generations a year depending on conditions, and individuals may live up to three years.