The scorpion fly, despite its name, is neither a scorpion nor a fly. The name is a suggestion of the general appearance of the insect. They have four membranous wings that are the same size and shape. The head is rather elongated and points down in a beak-like fashion with the chewing mouthparts located at the tip of the beak. The genital segment of the male scorpion fly has an enlarged, rounded appearance. In addition, it curves up over the back of the insect, resembling a scorpion's tail. However, the tail is not an offensive weapon; it is used for grasping the female during copulation.
Scorpion flies are so unique they have been given their own taxonomic order: Mecoptera. They undergo complete metamorphosis and most are 0.4-0.8 in (9-22 mm) in length. The majority of the Mecopterans that are encountered in the wild constitute two of the five families: Panorpidae (common or "true" scorpion flies) and Bittacidae (hanging scorpion flies). The three remaining families, Panorpodidae, Meropeidae, and Boreidae, have a combined total of 14 North American species and are not very common.
The Panorpidae are, for the most part, scavengers. The larvae and the adults feed on dead animals, including insects with the occasional diet supplement of mosses, pollen, fruit, and nectar. The eggs are laid in the soil in small clusters, eventually hatching into larvae that have a caterpillar-like appearance. If the larvae are not on the surface feeding, they are in shallow burrows that have been dug in the soil. Pupation takes place in an elongated cell just under ground by the fourth instar larvae.
The Bittacidae are similar in appearance to the Panorpidae but lack the scorpion-like tail. In addition, the Bittacids are hunters. The second and third pair of legs are extremely long and raptorial (modified for grasping), thus preventing the insect from standing in a normal fashion. By hanging from the front pair of legs, the Bittacids reach for passing prey with the hind legs, hence the nickname "hanging scorpion fly." Prey often includes spiders, moths, flies, and other small, soft-bodies insects.