Thief ants possess small stingers on their oblong abdomens. Both nymphs and adults have long, paired cerci projecting from the tip of their abdomens. Shrimp are swimming crustaceans with long narrow muscular abdomens and long antennae. Widow spiders are large, shiny house spiders with relatively spindly legs and deep, globular abdomens. These males also have visible outlines of the testes through the skin of their abdomens. Some species of "Gasteracantha" have very long, horn-like spines protruding from their abdomens. Their queens are wingless and have abdomens that expand significantly during egg production. Birdeaters have hair on their bodies, abdomens, and legs. Like most other insects, moths pick up these sounds using tympanic membranes in their abdomens. Their narrow wings and streamlined abdomens are adaptations for rapid flight. Their abdomens are pale yellow to white. Females can be distinguished from males by their wider abdomens and smaller second pereiopods. However, when they flee, they swim backward quickly by curling and uncurling their abdomens. Females with incomplete markings or all-black abdomens occasionally occur. Adults have black backs and white abdomens.