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Battle of the Bugs: Oak Leaf Gall Mites

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Battle of the Bugs: Oak Leaf Gall Mites

By George Giltner, Adv. Master Gardener, MS Biology

2015 oak gall mites

Welts from Oak Gall Mites

Have you ever raked leaves, gathered them, and then later develop red welts on your face, neck, arms and upper body? Note that chiggers normally invade from the feet upward to the waist area, but these super itch bugs like the upper body. Welcome to a new invasive species, the Oak Leaf Gall Mite, that is invading our range.  This is an organism from Eurasia (Egypt, Germany, etc.), but has also been reported in Chile, India, and Australia. Outbreaks occurred in 2004 in Texas, Oklahoma, Missouri and other states and again in 2007.


The usual season for outbreaks is August to October when they rain down from trees.  If you observe browned and crispy edges on oak leaves – beware because you may be within range of some nasty, itchy bites.  If you are a curious person requiring evidence, get your magnifier out, then open the crispy leaf edge gall.  There you will find dead midge larvae and itch mite females with large abdomens. Actually the mites would prefer Oak Leaf Midge Gall Larvae or cicada egg nests, its normal hosts that are required for reproduction. However when that food source is depleted, they began their downward fall journey where they can be picked up by wind and possibly be blown with leaves into other trees.  When they land on humans, they crawl around for 4 to 5 hours, and then they dig in.


A good practice is to shower within 4 hours after an expected exposure to these mites.  Also be careful with infected clothing.  If you don’t, itch mite welts form into pimple lesions after 12 hours.  The neurotoxin bites can last up to 2 weeks with intensive itching.  Over counter topical anti-itch creams may help along with oral anti-histamines. But do not scratch due to possibility of bacterial infections.  Then you should have a medical visit skin infections.


According to Kansas State Research and Extension, “There is no research-backed, proven ways to control them (Oak Leaf Gall Mites) yet”.


Pyemotes herfsi, the Oak Leaf Gall Mite, is being investigated, and more of its life cycle and niche is being uncovered.  Studies have shown that the mites can fall from trees in numbers of up to 370,000 per day (Penn State University).  The typical host is the Oak Leaf Gall Midge that forms a leaf-marginal gall fold.  Trees commonly infected are pin oaks and other ‘red oak’ group trees.  Overwintering has been reported in oak leaves, in wood inside of wood-boring beetle larvae, and in grains where they feed on various stored-product pests.


Therefore this fall beware of the ‘fall of mites’ on ‘under the old oak tree’ picnics and hunting stands in oaks.  Load up on calamine lotion, if you do encounter these very itchy mites, but do not scratch!



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