Oak leaf itch mite – What’s eating you?

November 15, 2021

Will Summers, Master Gardener

Summer is over and cooler weather is soon to arrive to south-central Illinois. Before cold weather arrives, please be on the lookout for a mysterious itch that “mite” be in the air. This itch is caused by a tiny, almost microscopic, mite that, in lieu of finding its regular host, will prey on any warm-blooded creature. This is the oak leaf gall itch mite, or more specifically, Pyemotes herfsi.

There is little wonder why this mite belongs to the group of insect-like animals called “arachnids.” This includes all ticks, scorpions and even spiders. You may experience unexpected insect bites after spending time outside. The bites feel like a chigger bite, except they are not on your feet, ankles or in tight places between elastic and skin, or like a mosquito bite on your exposed skin. If the bites are a collection of two or more bites on your head, face, neck or chest, then you may be the victim of the oak leaf itch mite. Itch mites are common from Kansas to Indiana and Nebraska to Texas. Oak leaf gall itch mites reached serious proportions as recently as 2017 in Chicago.

The mite is approximately a tenth of a millimeter, or about 1/125ths of an inch long which makes it nearly invisible to all but the well-magnified eye. This mite is so tiny that it may be carried some distance from the source by the breeze. Oak leaf gall itch mites are parasitic on the oak leaf gall midges and a variety of other insect hosts. The oak midge infests pin oaks, but may be found on red and black oaks in our area as well. Unfortunately, as the mite hatches and falls to the ground or floats on the wind, it will feed on whatever it lands on before reaching the ground. The mite bites within 4 hours of landing on its victim. The bites begin to itch within 10 hours after being bitten and last 10 days to 2 weeks. The bites appear as red, raised welts with a raised blister in the center.

A new problem has arisen. Recently, the oak leaf gall itch mite has found its way to preying on cicada egg masses. The itch mite life cycle coincides with the timing and location of the cicada. The female itch mite lays her eggs inside developing cicada eggs. The mite eggs hatch in a week after feeding on, parasitizing and devouring their host insect. The apparent abundance of itch mite coincides with this summer’s periodic cicada hatch.

The oak leaf gall itch mite life-cycle takes about a week and the female will lay 200 to 300 eggs in her lifetime. The male mite dies after mating. Subsequently, due to the short life cycle, large numbers of eggs and no natural control, this insect has the potential for a very rapid population explosion. It is calculated that one pin oak tree produces 300 to 400 thousand mites each day. Oak leaf gall itch mites begin to hatch in late July and their populations continue to build through the fall until cold, wet weather ends their habitat for another year.

What causes the itching sensation is extremely potent neurotoxin and mite saliva. The mite’s toxin is so strong that it can kill another insect 166 thousand times its size. However, it is administered in such tiny doses that in humans only the itch may be felt. As they fall from the sky, itch mites land on the head, face, neck or shoulders of their human victims. However, pets, wildlife, birds, livestock, or any warm-blooded animal will likely fall prey to their itch. Therefore, avoid sitting under infested trees, shower soon after coming indoors and be aware to keep skin covered while raking oak leaves this fall. If you come down with bites, apply anti-itch ointment or an antiseptic solution, but do not scratch.

The oak leaf itch mite was only discovered in the Midwest in 2004 but has since been detected over a wide area of the region. The itch mite is known in China, and India, as well as North America. There is no control except for weather and seasonal change to control this predator. Insect repellants will not work because the mite will bite you through the repellent. Pesticides do not work because there is no way to contact, or even know how many or where the mite might be. The better way is to avoid the bites by being aware of their occurrence. In particular, this fall while you are raking oak leaves, you are likely to encounter the mite as it lingers in fallen leaves.

Fascinating and interesting creatures share our world. For more information regarding oak leaf gall itch mite or any other gardening question, please contact your local Master Gardener, the University of Illinois Extension Service, or your local public library.

The Oak Gall Itch Mite is a tiny, irritating insect you are likely to encounter while raking leaves this fall.

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