Oak Mite Outbreak

By Jeff Rugg

October 6, 2009 4 min read

Q: The doctor diagnosed me as having been bitten by oak mites. What can you tell me about their life cycle, so I can keep from being bitten again? The bites are horrible. They have been itching 24 hours a day for a couple of weeks, and nothing seems to help.

A: While there are several species of microscopic mites, the oak leaf gall mite has been diagnosed as being responsible for several outbreaks on humans. Mites have eight legs like spiders — they are not classified as insects, which only have six legs — and they are only 125th of an inch long.

The normal life cycle of this mite is very strange. Most animals in this size range go through a sequence of egg, larva, pupa and adult. After the female of this mite species mates, the eggs develop into adults while still in her abdomen. Several hundred adults can be born in just a few days. As soon as they are born, they can mate and start the cycle over again.

The normal food source for the mite is the egg or larval stage of other insects. One common food source is a tiny gnat-sized fly called an oak leaf edge-gall midge. The female midge lays her eggs in an oak leaf. The larva is so small that it lives inside the thickness of the oak leaf.

The female oak mite needs to feed on blood to develop the miniature adult babies developing in her abdomen. She bites the larva of the midge and injects it with powerful neurotoxins.

In the late summer and fall, unaffected midge larva drop out of the leaves to spend the winter as a pupa in the soil. Other insect populations are also declining at that time. The mites have less food in the oak tree. Some pregnant females will stay in oak leaves to spend the winter. Some of these leaves fall off, while some will stay on the oak tree. The rest of the mites will fall off the tree or float away on the wind. They seem to do this more in the evening than during the morning. Since they are so small, they can float through screens and clothing.

Working with oak leaves or doing activities under oak trees can allow the mites to get on a person. They seem to not bite immediately, but eventually if they are not washed off, they can bite. When they bite, they inject the neurotoxin that kills their normal foods.

The mites cause red welts that look like chigger bites, but they are not usually found on the legs like chigger bites. Typically, the reaction is intensely itchy, but scratching doesn't offer relief and can be painful. Over-the-counter anti-itch creams may not work. Scratching can lead to infections.

Without an expert's help, it is almost impossible to know if an oak has the mites. Red, pin and white oaks can get the mites, but burr oaks don't. Oak trees occur everywhere across North America. People have homes, parks and lots of activities under oak trees, yet mite bites appear to be very rare. Areas with documented outbreaks in one year may continue to have bite occurrences. Cool and wet weather does seem to help some insect and mite populations expand, which is the type of weather experienced by large parts of the country this past summer.

You do not need to cut down your trees or spray them with insecticides. There is some evidence that an insecticide used for chiggers on lawns may help kill the current mite population. A mosquito repellent may be useful when working outside, but there is less evidence for that. Wearing gloves and long sleeves when raking and cleaning up leaves may help, but the mites could congregate in the tight areas of clothing.

Since they feed on insect larva, they cannot live inside your house. If you have the red welts and uncontrollable itching, you should see a doctor.

E-mail questions to Jeff Rugg, University of Illinois Extension at [email protected] To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.

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