Warm weather means the return of mosquitoes, ticks ... and tiny biting mites known as chiggers. They're nearly invisible. But if they bite you, you'll know it.
What are chiggers, anyway?
Chiggers are the immature stage of some mites. They're tiny — about 1/150 of an inch in diameter — and they have six legs. But they're not insects: the adult mites have eight legs. "They are more closely related to spiders and scorpions," explained Ashley Dowling, an acarologist at the University of Arkansas.
Only the larvae bite. As adults, the reddish, furry mites are predators or scavengers. "They just walk around and eat little insects or other mites, or feed on eggs of insects," Dowling said. "They pretty much leave us alone."
In fact, even the larvae aren't really looking to bite people. Dowling said they prefer reptiles, amphibians and other small animals. "Snakes and lizards," Dowling said "Some of them feed on frogs, birds, on mice. That’s normally what they’re looking for."
But even if we're not an ideal host for them, chiggers will feed on us, too, if they get the chance.
Where do chiggers live?
Everywhere! OK, not quite. But chiggers are all over the lower Midwest.
"Missouri is definitely chigger country," Dowling said. "I’m in northwest Arkansas, not far from Missouri, and this part of the country — Oklahoma, Arkansas, Missouri, Nebraska, Iowa — these are all primary chigger areas. If you get further south, they tend to get even worse."
Chiggers generally live in dense grass, bushes and brambles. "Those are excellent chigger habitat," Dowling said. "But you’ll get them in manicured lawns, too." Chiggers can't move very fast or travel very far. "And so they’ll often just hang out on vegetation, low to the ground, hoping for another mouse or a snake to come by."
Why do chigger bites itch so much?
That itching may not be what you think. "There are a lot of myths out there about chiggers," Dowling said.
For example: chiggers don't suck blood, like a mosquito. And contrary to popular opinion, they don't burrow into the skin. "They pierce the outer layer, and typically, as soon as you start itching, the chigger isn’t even there anymore," Dowling said. "They’re so small that if we scratch it, if we brush up against something, it tends to dislodge the chigger."
Still, what chiggers actually do to us is pretty gruesome. Once they pierce our skin with their mouthparts, they secrete saliva full of digestive enzymes. "Those enzymes, they dissolve the skin cells inside there," Dowling said. "And then they’re basically drinking those dissolved skin cells."
Our skin reacts to the assault by forming a hard tube, called a stylostome, that the chiggers use like a straw to suck up more skin cells. The itching we feel is a reaction to that irritating stylostome and the enzymes.
Dowling said the idea that covering chigger bites with nail polish or something similar will stop the itching is just another myth. "Or at least, you’re not doing it to suffocate the chigger," Dowling said. "The chigger is long gone."
Dowling said if you think you've been bitten, the best thing to do is use a wet wipe to clean off exposed skin and get rid of any chiggers that might be digging in. Taking a shower and putting hydrocortisone cream on the affected areas as soon as possible can also help reduce the itch.
How can I avoid getting bitten?
If you live in Missouri, don't go outdoors in the spring, summer or fall.
But avoiding overgrown trails is probably a good idea.
And like mosquitoes and ticks, chiggers can't bite you if they can't get to your skin. "Being covered up works well," Dowling said. He recommends wearing pants and long sleeves, and tucking your pant legs into your socks.
Dowling said mosquito repellents like DEET may not deter chiggers, but insecticides like permethrin — which you spray on your clothing, not your skin — will kill them.
"And then there are other things," Dowling said. "People make this mixture with sulfur, sulfur powder, maybe talcum powder. They sprinkle that on their pant leg and socks and swear that keeps the chiggers off of them. I know my mother-in-law swears by it."
But some people are just more sensitive to chigger bites than others. "If you went out hiking with five people, you could all walk through the exact same chigger-infested area, and you could all react differently," Dowling said. "Ranging from someone with hundreds of bites to someone else in the group not actually exhibiting any bites."
Dowling said chiggers don't bother him much. But if I get anywhere near them, I end up covered in red, rash-like bumps that itch like crazy for weeks.
On the plus side, unlike some mosquitoes and ticks, chiggers don't spread disease. "Not in the U.S.," Dowling said. "Not as far as we know."
I'll try to take comfort in that, the next time I get bitten.
Follow Véronique LaCapra on Twitter: @KWMUScience