The family Staphylinidae contains some 20,000 known species of beetles. It is the most numerous family of beetles found in North America, where there are nearly 3,000 species.

Known as rove beetles, members of this family are small-the largest species seldom reaches more than V2 inch in length. Rove beetles are usually brown or black in color. Their bodies are usually long and slender, and capable of lightning-swift contortions.

The most distinctive structural feature of the rove beetle, however, is the extreme shortness of its wing covers, or elytra. Only about twice as long as they are wide, the elytra of the slender rove beetle leave a considerable portion of the abdomen exposed. A strong flyer, the rove beetle folds its well developed back wings parachute fashion under its tiny elytra when not in flight.

Members of this family are found in a variety of habitats. Some live on carrion; others are found in piles of garbage, in excrement, in humus, and in fungi. Some species of staphylinids inhabit the nests of birds, mammals, and insects, especially ants and termites.

The rove beetle's relationship with its host in these situations can take a variety of forms. Some species cohabit peacefully with the nest's original occupants, while others are predaceous, feeding on the eggs and larvae of their hosts. Members of the genera Homalota and Quedius, for example, enter the homes of bark beetles and eat their larvae.

Those rove beetles that abuse their hosts hospitality are often attacked and driven from the nest by its outraged residents. Staphylinids are also found in widely diverse climates: certain species thrive in the tropics, and others are found in the Arctic.

When disturbed, a rove beetle will frequently raise the tip of its abdomen, giving the impression that, like a scorpion, it is about to sting its attacker. But despite this affectation, the rove beetle does not sting its enemies. The rove beetle's defensive weapons, in fact, are located at the other end of its body-a pair of long, sharp mandibles that usually cross in front of the head. Many novice coleopterists can testify to the rove beetle's painful bite. Some species also are armed with caustic secretions that can burn human skin.

Some species of rove beetles have formed complex relationships with the members of other families of Coleoptera. Rove beetles of the genus Bledius, for example, cohabit with ground beetles of the genus Dyschirius.

These rove beetles densely populate sandy shores and coastal swamps where they feed on algae. One species of rove beetle, Staphylinus olens, on the other hand, preys on sexton beetles in the carrion graves where they raise their young.

Paederus. Rove beetles of this genus are usually brownish-orange or terracotta in color, marked with dark patches and shiny green or dark blue wing covers. Extremely mobile beetles, they tirelessly explore the gravel beds of streams. When disturbed, these rove beetles emit pederine, a substance that can seriously inflame human skin. The African species Paederus sabaeus is particularly dangerous in this respect.

Lomechusa. Members of the genus Lomechusa produce secretions that attract hymenopterans, members of an order of insects that includes sawflies, ants, bees, and wasps. These secretions are so appealing to the Hymenoptera that they will often neglect their young to follow the scent. The Lomechusa feed on food regurgitated by these Hymenoptera and also prey on their eggs and larvae.