Chiggers are tiny pests that cause intensely itchy bites, often experienced while enjoying the outdoors. These organisms are the larval stage of mites, which are arachnids related to spiders and ticks. While the resulting red welts and severe itching are a common summer frustration, chiggers in the United States are not known to transmit human diseases. Understanding the biology of these mites and their preferred habitats helps in avoiding the painful skin reaction they cause.
Identifying the Pest
Chiggers are the parasitic larval stage of mites belonging to the family Trombiculidae, making them arachnids related to spiders and ticks. The larvae are nearly microscopic, measuring 0.15 to 0.3 millimeters, and are typically yellowish to light-red with six legs. Adult mites are larger, have eight legs, and are non-parasitic, feeding on small organisms and insect eggs in the soil.
Only the larval stage feeds on vertebrates, including humans, who are considered accidental hosts. Chiggers do not burrow into the skin or suck blood. Instead, they attach to the skin and inject a digestive enzyme. This enzyme dissolves skin cells, which the chigger ingests as a liquid meal through a feeding tube called a stylostome. Intense itching and reddish welts begin hours later as the body reacts to the enzyme and the stylostome, often long after the chigger has detached.
Mapping the Affected Regions
Chiggers thrive in warm, humid climates, making them highly prevalent across the central, southern, and southeastern United States. Problematic regions include the Southeast, the humid Midwest, and states like Texas, Oklahoma, Georgia, and Florida, where the warm season is extended. Activity begins in the late spring, peaks throughout the summer, and continues until the first frost, as they are most active when ground temperatures are between 77 and 86 degrees Fahrenheit.
Chiggers are concentrated in specific habitats that offer shade and moisture. They are typically found in transition zones, such as the borders between wooded areas and open fields, or along the edges of swamps and brush thickets. Tall grasses, weeds, berry patches, and overgrown areas near water sources provide the low-lying vegetation where the larvae wait for a host. They become inactive when temperatures fall below 60 degrees Fahrenheit and are rarely found in arid climates, high mountains, or the far northern United States.
Managing Bites and Prevention
Managing chigger exposure involves both prevention tactics and post-exposure treatment. Prevention centers on creating a barrier and a chemical deterrent before entering a suspected chigger habitat. Wearing long pants and long-sleeved shirts, especially tucking pant legs into socks or boots, minimizes the exposed skin available for chiggers to contact.
Specific insect repellents are effective deterrents when applied correctly. Products containing DEET should be applied directly to exposed skin. Permethrin-based products are designed for clothing and gear, where they act as an insecticide to kill the mites. After being in a chigger-infested area, taking a hot shower or bath immediately and scrubbing the skin vigorously can dislodge any unattached larvae, reducing the number of bites.
Chigger bites typically appear as intensely itchy, small, red welts or bumps, often clustered in areas where clothing fits tightly, such as the waistline or ankles. Treatment focuses on alleviating the itching to prevent scratching, which can lead to a secondary bacterial infection. Over-the-counter anti-itch creams containing hydrocortisone or calamine lotion are recommended for topical relief. Taking an oral antihistamine can also help minimize the allergic reaction, which can persist for a week or more.