Indiana trees are now at risk of a new nuisance known as the oak leaf gall mite, warns the Purdue University Extension Service.

The oak gall mite, which has been a nuisance in Nebraska, Kansas and Colorado, is a parasite on a parasite that has recently been found in trees around Chicago. Its primary host are insects that are parasitic on oak trees; the parasites feed on the tree’s leaves, causing a deformity of the leaf called a gall. The oak gall mite lives in the gall, said Tim Gibb, a Purdue Extension entomologist.

"Unlike the name might suggest, the oak gall mite is not just found on insects in oak trees," Gibb said. "We know for sure they are on oak trees, but because many of those insects also make galls on other trees there is reason to believe they are on other trees as well."

When there are not enough insects acting as hosts for the mites, humans and animals become secondary hosts.

"Don't panic yet. These mites do not carry diseases and are very similar to chiggers," Gibb said. "They are strictly a nuisance and there is no need to stop outdoor activities."

The oak gall mite is hardly visible to the naked eye, measuring about 100th of an inch, or the width of three human hairs.

When the mites get on people, they typically go to the pores or hair follicles.

"Once they pick a spot they inject their saliva, which desensitizes the skin around it and then suck lymph from the body. The person won't know until four- or five-plus hours later when the skin becomes sensitive and develops a rash or welt that itches,” Gibb said.

The soft-bodied mites die easily and drop off after feeding.

The mites can be dispersed in the air, but people are at a higher risk if they work in trees or in direct contact with leaves that have galls. Gibb urges people to wear long pants, long-sleeve shirts, a hat and insect repellent when outdoors. People returning from areas heavily populated with oak trees should shower with plenty of soap, which will kill or wash off the mites. Clothing should also be removed and washed, since the mite can remain in the fabric for several days.

Posted 10/9/2007