The chigger is the parasitic larval stage of a mite belonging to the family Trombiculidae, making it an arachnid, like spiders and ticks. These nearly invisible pests are typically less than 1/100 of an inch (0.3 mm) long. Only this six-legged larval stage is parasitic, seeking a host to feed on skin cells before developing into a non-parasitic nymph and adult.
Common Residential and Wild Habitats
Chiggers thrive in outdoor environments that provide warmth, moisture, and dense vegetation. These conditions support the high humidity levels they prefer, which protects them from drying out. In wild settings, chiggers are found in low-lying, damp areas, such as along lakes, streams, and in swampy regions.
They congregate in areas with heavy vegetative cover, including tall grasses, weeds, thickets, leaf litter, and rotten logs. Chiggers are particularly abundant in transition zones, like where a manicured lawn meets a wooded area or an overgrown field. They stay close to the ground, usually on vegetation no more than 12 to 15 inches high, as they do not climb high up into trees or tall bushes.
In residential settings, chiggers persist in home lawns, especially if the grass is allowed to grow tall or if areas are poorly maintained. Brush piles, dense shrubbery, and overgrown garden areas create sheltered microclimates for them to flourish. The presence of small mammals and reptiles, which are their preferred natural hosts, can also indicate a localized chigger population.
How Chiggers Transfer to a Host
Chigger larvae employ “questing” to find a host, which involves climbing to the tips of low-lying vegetation. From this elevated perch, they wait for an unsuspecting animal or human to brush past. They do not jump or fly; transfer occurs only through direct contact with the infested foliage.
Once on the host’s clothing or skin, the chigger will explore for several hours before feeding. Larvae crawl upward until they encounter a location where the skin is thin, tender, or where clothing fits tightly against the body. Common feeding sites include the ankles, behind the knees, around the waistline, and in the armpit and groin areas. The tight bands of socks, underwear, and belts trap the mites, prompting them to settle and begin feeding.
Understanding the Bite and Irritation Mechanism
A common misconception is that chiggers burrow underneath the skin, but this is inaccurate. The six-legged larvae pierce the skin using their mouthparts, known as chelicerae, and inject a digestive enzyme into the wound. This enzyme dissolves the surrounding skin cells, which the mite then ingests as a liquefied tissue slurry.
The host’s immune system reacts to the foreign enzyme by hardening the tissue around the feeding site. This reaction forms a hardened tube called a stylostome, which the chigger uses like a straw to consume the digested cells. The intense itching and irritation are caused by an allergic reaction to the injected enzyme and the hardened stylostome. Symptoms, including the characteristic red welts, typically appear hours after the chigger has attached, often after the mite has already been scratched off.