Chiggers are microscopic pests that cause intensely itchy welts, often encountered after walking through overgrown fields or woods. These organisms cause a form of dermatitis known as trombiculiasis. While often mistaken for insects, chiggers are actually a type of mite, placing them in the class Arachnida, alongside spiders and ticks.
The Biological Identity of the Chigger
Chiggers are the parasitic larval stage of mites belonging to the family Trombiculidae, commonly known as harvest mites. Only the six-legged larva, which is less than 0.3 millimeters long, seeks out a vertebrate host for a meal. This larval stage is the only one in the life cycle that feeds on humans, mammals, reptiles, or birds.
Once the larva is engorged, it drops off the host to continue development. The subsequent nymph and adult stages have eight legs and are not parasitic to people. These mature mites are harmless to humans, feeding instead on plant matter, insect eggs, and small arthropods in the soil.
The Etymological Confusion of the Name
The name “chigger” is a phonetic corruption of “chigoe” or “jigger,” which refers to the Tunga penetrans, a type of burrowing flea. This flea is an insect, not a mite, and is primarily found in tropical and subtropical regions, including Africa and South America.
The jigger flea burrows into the skin, typically the feet, to lay eggs, causing a serious inflammatory disease called tungiasis. Early explorers or colonists in the Americas encountered the intensely irritating mite and mistakenly applied the name of the well-known tropical flea due to the similarity in skin irritation. This name transfer persisted despite the two creatures belonging to entirely different classes of arthropods.
Addressing the Misconception of the Bite
A widespread misconception is that chiggers burrow into or under the skin and must be smothered for removal. In reality, the chigger larva does not burrow or suck blood; it attaches only to the surface of the skin. Once attached, the mite injects a digestive fluid containing proteolytic enzymes into the host’s skin cells.
These enzymes dissolve the host’s tissue, which the chigger then ingests as a liquid meal. The host’s immune system reacts to this foreign substance by hardening the surrounding skin, forming a tube-like structure called a stylostome. The chigger uses this hardened tube as a straw to continue feeding on the liquefied tissue. The intense, persistent itching is an allergic reaction to the enzymes and the stylostome, which remains embedded even after the larva has finished feeding or been brushed off.