Chigger Basics

Whether for work or recreation, now is the time of year when we take to the great outdoors for picnics, gardening, backpacking or fishing. It is also the time of year when we find ourselves dealing with biting pests. One of the most notorious biting pests is the chigger. The threat of chigger bites exists from May until the first killing frost.

A chigger is the parasitic immature stage of the mite Trombicula alfreddugesi. The adult mites are harmless. Chiggers are microscopic (about 1/50 of an inch) and normally live on rodents and birds, where they must feed in order to complete their development. They do not suck blood or transmit disease. Humans are only accidental hosts, and we usually encounter chiggers in moist areas with low-growing shrubs or tall grasses and weeds. Within these areas chiggers typically have a clumped distribution. A person sitting in one spot may be heavily attacked, while a person a few yards away may not be bitten at all.

When a chigger attaches to a human, it moves upward and settles down to feed in an area where clothing fits tightly against the skin (i.e., socks, waistlines, etc.). When feeding, chiggers form a tube within the skin tissues called a stylostome, which is used to inject digestive enzymes and suck up dissolved skin tissues. The discomfort associated with this feeding causes intense itching in humans.

Scratching dislodges the chigger and kills it; however, the feeding tube remains and will continue to cause discomfort until the body has had time to neutralize the enzymes and repair the damaged tissue. Dissolved tissue will ooze out of the bite each time it is scratched and form a hardened cap, which is a distinct feature of chigger bites. Scratching also increases the risk of secondary infection and should be avoided. You can treat the itch using medicated creams, but only time will heal the tissues.

The best defense against chiggers is to control chigger habitats and avoid going into areas that might be chigger-infested. Keeping grass and weeds trimmed around the home and garden will eliminate the majority of problems. However, if you must go into chigger habitats, wear appropriate clothing. Avoid wearing sandals, shorts, or sleeveless shirts. Instead, wear clothing that is tightly woven. Tuck pant legs inside of socks and button collars and cuffs to keep chiggers on the outside of clothing. In addition, you can use mosquito-type repellants on the outside of clothing to repel chiggers.

Although most outdoor activities are fun and relaxing, a case of chiggers only causes grief and discomfort. Hopefully, you can minimize the effects of chiggers by avoiding their habitats, dressing appropriately, and, if bitten, using appropriate precautions to treat the bites.

Richard M. Houseman, Department of Entomology UMC (573) 882-7181