May 28 - Eutrombicula alfreddugesi

If you’ve ever had chiggers, you know they’re really, really irritating. These are the parasitic larval stages of free-living mites, and Eutrombicula (Trombicula) alfreddugesi is the most familiar in North America. Chiggers perch on foliage, climb aboard passing pedestrians, and find their way to the new host’s skin. Once there, the tiny mite positions itself atop a hair follicle or pore, and secretes highly digestive saliva that liquefies the host’s skin cells. The surrounding cells harden in defense, forming a stylostome. But it’s a poor defense – the stylostome helps the parasite by functioning as a straw for the chigger to slurp his slurry of dead cells. Moreover, the stylostome contributes to that really, really irritating inflammatory (i.e., itchy) response in the host’s skin. Thankfully, E. alfreddugesi is not a vector for disease, and the discomfort subsides after a few days.

Eutrombicula alfreddugesi isn’t picky, and infects numerable hosts besides humans. It’s a parasite of many vertebrates, including birds, mammals, and reptiles (the photo shows several chiggers on the dewlap, or throat fan, of an anole lizard). In fact, host habitat is probably more important that host taxonomy for this species. Chigger infestations usually occur in warm, shady, and moist environments, as this is best for the soil-dwelling and detritus-eating adult stages (meaning that this is where most eggs are laid). Similarly, these chiggers prefer certain areas on the host, from the undergarment areas of humans, to the “mite pockets” of some lizards. Mite pockets are small, but relatively deep, cavitations that are typically located just behind the lizard’s forelimbs. When these lizards have mites, most are in the pockets, leading some scientists to speculate (and others to dispute) that a pocketful of mites is advantageous for the lizard. The chiggers are bright red, and on a drab lizard, they present a flashy spot of color that can be turned on and off as the lizard moves its legs.

Contributed by Bryan Falk.