Master Naturalists: Chiggers vs. people - and the winner is?
By Paul and Mary Meredith
May 10, 2012 at 12:10 a.m.
Mary won the chigger-attracting contest when we were setting beetle traps in Point Comfort last week. So now, she's got lots of red welts and will itch-and-scratch for several days. What is all this - and how do we avoid it in the future?
First, learn more about chiggers. They're small, but big on authoritative Internet sources.
Things called "chiggers"
Chiggers are arachnids - like spiders - closely related to ticks. They're mites whose larval stage feeds on vertebrate animals, preferably reptiles or birds. To survive, they sometimes victimize targets of opportunity, like humans. As adults (after metamorphosis) they become vegetarians. (It's interesting that chiggers that feed specifically on humans in Asia and on Pacific Islands do not cause itching).
Chiggers are born red, no blood-sucking required. And a very well-fed chigger turns yellow. They measure less than 1/150 of an inch, so more than 1,000 could line up across a sheet of paper (81/2 x 11 inches) and leave room for several hundred more. Under a microscope, you see they're ugly, maybe even enough to star in a science-fiction movie.
How they do it
It's a myth that they burrow into our skin and die there, thus making us itch. Some Southern pests do burrow, but chiggers are too large to fit in our pores and are not equipped to burrow.
They bite us - somewhat like ticks do, attaching themselves to us by using specialized mouth parts (chelicerae) - in depressions in our skin, usually skin pores or hair follicles. They can penetrate only thin skin, or where skin wrinkles or folds. They prefer women's and children's more tender skin.
But so far, there's nothing to make us itch. What does that - so very much for so long - is the chigger's injecting saliva into us. Their saliva contains a powerful digestive enzyme that literally dissolves the skin cells it contacts. What the chigger ingests for food is the liquefied tissue, never blood.
Chiggers usually go unnoticed for several hours after they bite. That's when they inject their saliva and begin feeding. In defense, our bodies harden the skin cells around their saliva, forming a straw-like feeding tube (stylostome).
Our itching is an allergic reaction to the stylostome. The longer the chigger feeds, the worse our welts become. But welts never get large enough to "engulf" the chigger. The red dot in the welt is the stylostome, not the chigger.
Chiggers run around except when feeding, are fast, and are attracted to anything new. Getting from your shoe to your beltline (a favorite target area) takes only about 15 minutes - amazing, given their size. They can penetrate your clothes, but look for easy openings, hem lines perhaps.
Get rid of chiggers
The best way to eliminate chiggers is just remove the habitat adult and juvenile chiggers favor. Clear away brush and weeds, keep grass cut close to the ground, and remove conditions that attract small animals that can be chiggers' hosts. Chiggers seldom survive in well-groomed areas.
Sources: Missouri Department of Conservation; University of Missouri Extension; Arizona Cooperative Extension
Paul and Mary Meredith are master naturalists. Contact them at firstname.lastname@example.org.