Chiggers are tiny arachnids belonging to the mite family, commonly encountered in grassy and wooded outdoor environments. These pests are best known for the intensely itchy bites they leave on the skin of people and animals. Their small size makes detection before a bite occurs nearly impossible. They are a widespread nuisance, especially in warm, humid climates.
The Size and Visibility of Larval Chiggers
The chigger stage that bites humans is the larva, which is nearly microscopic and extremely difficult to see with the unaided eye. These six-legged larvae typically measure between 0.2 and 0.4 millimeters in diameter. This minute size means they are often overlooked as they crawl across clothing or skin looking for a feeding site.
Adult mites are slightly larger, reaching about 1 millimeter in size and are often bright red, making them more noticeable. However, adults are not parasitic and do not bite humans. If spotted, the larvae may appear as tiny, reddish specks, sometimes gathered in groups, but this usually requires magnification.
The Life Cycle and How Chigger Bites Occur
The chigger life cycle includes the egg, larva, nymph, and adult stages, but only the larva is parasitic and feeds on vertebrates. After hatching, the larvae climb onto low-lying vegetation, waiting for a host to pass by. They attach to a host as it brushes against the vegetation, often migrating to areas where clothing is tight or the skin is thin.
Once a feeding site is found, the larva attaches its mouthparts to the skin; it does not burrow underneath the surface. Instead, the chigger injects a digestive enzyme through its saliva that breaks down skin cells. The host tissue reacts by hardening, which creates a feeding tube called a stylostome. The chigger feeds by sucking up the liquefied skin cells through this tube for several days before dropping off and molting into the harmless nymph stage.
Identifying the Rash and Reaction
The primary way to identify exposure is by recognizing the resulting skin reaction, known as trombiculiasis. The characteristic rash appears as red, raised welts or bumps that may resemble pimples, blisters, or hives. These lesions are often clustered together, sometimes appearing in a line.
The intense itching is typically delayed, starting several hours after the chigger has begun feeding, and can last for several days. Bites are most often found in areas where clothing restricts movement, trapping the larvae against the skin, such as around the waistline, ankles, or armpits. The severity of the reaction is a direct result of the host’s immune response to the stylostome and the digestive enzymes left behind.
Prevention and Immediate Removal
Preventing chigger bites starts with knowing their habitat, which includes damp, shady areas with tall grasses and dense vegetation. Before entering these environments, protective measures include wearing long-sleeved shirts and long pants tucked into socks or boots. Applying insect repellent containing DEET to exposed skin and treating clothing with permethrin can reduce the chance of attachment.
If you suspect exposure, the most effective immediate action is to take a hot, soapy shower or bath as soon as possible. Scrubbing the skin will help dislodge any larvae that have not yet attached or begun feeding. Any clothing worn during the exposure should be removed immediately and washed in hot water and dried on a high heat setting to kill remaining mites.