Vein pocket galls are visible on an oak leaf in this photo from Kansas State University Research and Extension. Almost-microscopic oak leaf itch mites burrow into these growths before falling from the leaves and biting whatever they land on, often leaving large red welts.

It’s officially fall: The leaves are turning color and dropping off the trees. And falling with them are almost-microscopic biting insects that can leave itchy welts on your skin.

The insects, oak leaf itch mites, are in the area for the second year in a row, said Marlin Bates, a horticulture agent at the Kansas State University Extension in Douglas County. And this year they’re more widespread than before.

The arrival of the mites is a cyclical event that’s not completely understood, Bates said, but it’s tied heavily to another insect, a type of fly that lays its eggs, called midges, on the leaves of oak trees.

An oak leaf itch mite

Once laid, the midges force the oak leaf to react by surrounding the intruder with a growth, called a vein pocket gall, Bates said. The mites then bury themselves in the gall, which protects them from the elements, and feed on the midges.

“What’s happening in these midges is the mites are having their young, who will eventually fall onto the ground,” Bates said. “They’re going to be falling on the ground, underneath the leaves, and they’re like specks of dust, and if they’re flying around, they’re going to bite whatever they land on if they’re alive.”

Bites from the mites can leave large red welts, more similar to a mosquito bite rather than a chigger bite, said Andy Dean, a physician assistant at Kansas Medical Clinic.

“They aren’t necessarily just on exposed areas, either,” Dean said. “The mites are tiny and can pass through loose clothing.”

Once bitten, over-the-counter creams such as calamine lotion or hydrocortisone cream and anti-itch creams can help with the welts, Dean said. Severity of the reactions can vary from person to person as well, he added.

Avoiding the mites can be difficult, Bates said. Spraying the trees won’t kill them because they’re protected by the leaf’s galls.

Insect repellents applied to the skin don’t help much, either, Bates added. Rather, the best course of action is to wear hats, long pants and long-sleeved shirts and to avoid contact with leaves and the ground.

If a person does come into contact with the ground or leaves, which is common enough this time of year, Bates said, showering can help keep the insects off.

“It takes about three hours for them to settle on you to take a bite,” he said. “Some people say it can happen in shorter amounts of time, however. But shorter periods of being exposed is better than hanging out in a lawn chair under a tree for three to six hours at a time.”

Although avoiding the mites can be difficult, Bates said, they’re not around for much longer, and they likely won’t be back next year.

“It’s a nuisance, but it’s a problem for a short period of time,” he said. “They’re not even likely to last all the way through the warm part of the season. I don’t think we’ll have to wait until the first frost.”