Week Eleven: Chigger Mite

Common Name: Chigger Mite

Scientific Name: Leptotrombidium sp.

Not-So-Fun Fact: Chigger mites transmit scrub typhus, which is also referred to colloquially as tsutsugamushi fever and scientifically as Orientia tsutsugamushi. Symptoms of scrub typhus begin as influenza-like but eventually cause fatal damage to the cardiovascular system, the lungs, and the kidneys if left untreated.

Domain: Eukaryota

Kingdom: Animalia

Phylum: Arthropoda

Class: Arachnida

Order: Acari

Family: Trombiculidae

Genus: Leptotrombidium

Description: The chigger mite is an ovoid arachnid so small that its sharp mouth cannot penetrate the skin far enough to suck directly from a blood vessel (for the actual mode of feeding, see Nutrition). This is a quite different organism from its harmless though irritating cousin the harvest mite, which in the United States is often referred to as a chigger.

Environment: Chigger mites inhabit low, damp grass and woodland areas in Asia, Australia, and the surrounding island archipelagos. During World War II, soldiers fighting in these areas were extremely susceptible to scrub typhus because their clothes were impossible to fully seal against the depredations of the mites and because of the necessity of marching through fields of tall kunai grass, a favorite haunt of the chigger mite.

Reproduction & Development: Chigger mites reproduce sexually and lay eggs. The larva of the chigger mite ingests one blood meal in its short childhood before molting and becoming an adult. The reason the chigger larva is able to pass on scrub typhus while only feeding once is that chiggers are capable of a process called “transovarial transmission.” In this process, the adult female becomes infected with the disease and passes it on to her unborn offspring, producing larvae born infected with scrub typhus.

Nutrition: The chigger mite’s single blood meal is made through a tiny feeding tube, which pokes minutely through the skin, liquefies the surrounding tissue, and sucks up this mixture of blood and fluid flesh. The irritation around a chigger bite comes mainly from its sloppy habit of leaving behind the feeding tube. The adult feeds entirely on plants and causes no harm to any animal except through its potentially diseased progeny.