Pill bugs are not actually bugs. These tiny creatures are members of Phylum Arthropoda and in the Order called Isopoda. Since they are actually the only crustaceans that spend their lives on land, they use trachea-like lungs in their hind legs to breathe . They are active at night. If salt was sprinkled on a pill bug, their lungs would dry out and they would proceed to die. Respiratory structures must be moist in order for diffusion of gases to proceed. Their shell allows them to reduce water loss when they roll up into a ball. They need to seek moist environments in which to live. Their presence indoors may indicate a dampness problem and they are considered pests.