The term "chigger" is a common name used to describe the larval stage of a certain group of mites. These mites are parasitic on warm-blooded animals during their larval development and produce bites that cause intense itching and the formation of small, reddish welts. Chiggers are active from spring to late fall but are most numerous in early summer when weeds, grass and other vegetative undergrowth are at their heaviest.
Chiggers are closely related to ticks and spiders and pass through the same four stages of development: the egg, larva, nymph, and adult. Adult chiggers spend the winter in protected locations and become active in early spring. After mating, female mites deposit their eggs in grassy or weedy areas. These eggs hatch into larvae (chiggers) that must feed on a warm-blooded animal in order to complete their development. After feeding, the larva detaches from the animal and finds a protected place on the ground where it develops through the nymph stage into an adult. Both nymphs and adults feed on insect eggs or small insects. Under favorable conditions, most chigger species complete their development in about 40 to 70 days.
In the larval stage, chiggers are orange, yellow or light red and are less than 1/150 of an inch in diameter. These larvae can barely be seen as they crawl on the skin surface of the host in search of an appropriate attachment site. When a suitable location is found, such as a skin pore or hair follicle, the chigger attaches its mouthparts to the spot. On humans, chiggers prefer places where the clothing fits tightly over the skin or where the skin is thin or wrinkled. Contrary to popular opinion, chiggers do not burrow into the skin or feed on blood. Instead, chiggers inject a digestive fluid containing enzymes that causes skin cells to rupture. The ruptured skin cell contents are then utilized as food. Unfortunately, the digestive fluid injected by the chigger causes affected skin tissue to become red and swollen. In addition, the bite area will itch intensely for several days even after the chigger has detached from the skin.
Control of chiggers in parks, recreation areas, or campgrounds is probably impractical. However, the likelihood of encountering chiggers in these areas can be reduced by applying personal insect repellents, wearing loose-fitting clothing, and avoiding sitting or reclining directly on the ground. In addition, taking a hot, soapy bath or shower immediately after returning from likely chigger-infested areas can remove most chiggers before they have had the opportunity to attach and feed. Chiggers may at times become established in homeowner lawns. In these cases, application of insecticides approved for turfgrass, such as those containing diazinon or chlorpyrifos, can be effective in reducing chigger populations.
This article originally appeared in the July 12, 1996 issue, p. 117.