House Dust Mite

The common name comes from the association of these mites, their skeletal parts, and/or fluids with hose dust. Although these mites do not bite, they are estimated to be responsible for the allergic reactions of some 500 million people worldwide and may be a factor in 50-80 percent of asthmatics. Although there are several species of house dust mites, this section will be restricted to the two most common species found worldwide. These are the American house dust mite, and the European house dust mite.

Recognition

Adults are about 1/64 inch long. Body oval, soft, somewhat dorsoventrally flattened. Color off-white to cream. Dorsum with fine straight/grooves not interrupted by sharp projections, without punctures not prolonged by a forked or pointed extension; external scapular hair/seta much longer and thicker than internal scapular hair; hysterosomal/rear shield absent; male posterior margin billowed, with 10 hairs; and metapodosomal venter without ringlike structures. Mouthparts with chelicerae relatively short, chelate; palpus short, simple apical sensillae short, unmodified. Stigmata absent. Legs with fourth pair inserted on posterior/rear portion of idiosoma/body; tarsi stout, usually not more than twice as long as adjacent tibia, tarsi of third pair of legs without spines, tarsal tip bearing a miniature claw surrounded by large discoid/bellshaped pulvillus. Genital opening an inverted "U". Anus with surrounding sucker plate surrounded by lateral, hardened ridges.

Habits

House dust mite development, fecundity, and longevity are very dependent on temperature, moisture, and an adequate food supply. Therefore, they select certain macroclimates within a structure which provides these needs.

These mites feed on sloughed human skin, spilled foodstuffs, fungi, and pollen. The average adult human sheds about 70-140 milligrams of skin scales each day, and about 180 milligrams of this material is sufficient to produce and maintain mass cultures of the European house dust mite for several months.

Highest concentrations of sloughed skin scales occur in bedding, mattresses, upholstered furniture, carpets, and in stuffed toys. Humans supply the necessary increase in moisture and temperature over ambient room levels when they frequent these areas. Bedding and stuffed furniture provide the best conditions because humans spend more time here, with carpeting being the least favorable because of lower moisture. A gram of dust vacuumed from carpeting may contain 100-400 mites, whereas a gram of dust from stuffed furniture may contain 3,500 or more mites. It has been estimated that a typical used mattress contains from 100,000 to 10 million house dust mites within it. Mite development in carpet on slab floors and floors over cool crawlspaces and basements probably is additionally slowed because of the cooler temperature.

The highly desiccant-resistant, prolonged quiescent protonymph is thought to be the stage which survives the dry conditions of the winter heating season and is the source of mites for population growth during the favorable periods which follow.