Gamasid Mites

(Gamasoidea), a group of mites of the order Parasitiformes. There are about 20 families. Gamasid mites have oval or elongated thoraxes (0.3-4 mm) covered with corselets. (A mite may have a single or divided dorsal and several ventral segments.) The body has many bristles, which are constant in number and position. The legs are six-jointed, with claws and suckers. The mouth organs are designed for bitting or puncturing and sucking. The chelicerae have pincers or are needle-shaped, and they project from tubular foundations, which are the fused coxa of the legs. The mites breathe through trachea, which open through spiracles on the sides of the body.

Gamasid mites lay eggs, but many are viviparous. There is a six-legged larva, which becomes an eight-legged first nymph, then a second nymph, and finally an adult mite. The cycle is short, and there can be tens of generations in a season. Most Gamasid mites are predators. They live in the soil, on the forest floor, and in manure and feed on tiny arthropods and nematodes. Some forms settle on manure and carrion insects. Representatives of some families (for example, Laelaptidae, Macronyssidae, and Dermanyssidae) have become parasites and bloodsuckers on reptiles, birds, and mammals. Their methods of parasitism vary. (There are forms living in the nests of their host animals, constantly on their bodies, or in their respiratory organs.)

Some forms attack man. Gamasid mite bites—for example, that of the chicken mite (Dermanyssus gallinae), which has multiplied widely in chicken coops—cause severe dermatitis. Gamasid mites are carriers of infectious diseases. The rat mite (Macronyssus bacoti), which lives in rat holes and cracks in building walls, can transmit rat-borne typhus and the plague. The mouse mite (Allodermanyssus sanguineus) transmits a fever disease—vesicular rickettsiosis. It appears that mites of the genus Hirstionyssus are capable of spreading tularemia among rodents in the natural regions for that infection.