In late July an article about oak itch mite bites and cicadas ran in the Washington Post in response to numerous reports of people in the DMV with red, itchy bites on their upper bodies. Several of us who work in Extension in this area have received numerous inquiries about these bites and their relation to Brood X periodical cicadas. I have researched what is known about this phenomenon and summarize the information here with a list of resources for more detailed information.
There is a mite known as the oak leaf itch mite, Pyemotes herfsi. The mite is most commonly known to feed on larvae of a midge (fly), Macrodiplosis erubescens, that forms galls on the edges of pin oak (Quercus palustris) leaves. Once the mites complete their development they drop from the tree, usually in late July through early fall for mites associated with the oak gall midge, and can be carried by wind for large distances. The mites land on animals and humans that they then bite. For more detailed information on this mite and midge go to the Kansas State fact sheet listed below.
The bite causes a reaction that is rash like and itchy. In the mid-west (Missouri, Nebraska), P. hersfi was first detected in 2004 and since has been reported associated with the oak gall midge to cause itching bites in humans from 2014-2017. Note that in addition to the oak gall midge, P. herfsi has been reported to feed on insects from at least 5 different orders with reports dating back as far as 1885 (ex. pine tip moth larvae, hackberry nipple gall).
The first confirmed (ex. mites found in egg nests) report of P. herfsi attacking eggs in periodical cicada egg nests (Brood XIII), and as the cause of an outbreak of bite rashes on humans, was in the Chicago area of Illinois during August – September in 2007. Although not directly found in periodical cicada egg nests, a species of Pyemotes, likely P. herfsi, was reported to be “the mite most commonly found” with periodical cicada egg nests among samples collected in 1885 in Michigan, Virginia and the District of Columbia.
In the DMV area, to my knowledge, no one has actually found P. herfsi mites in cicada egg nests. However, given the historical association of periodical cicadas and the mite, it is likely that the billions of Brood X periodical cicada eggs serve as a food source for the mites, and has resulted in an increase in mite densities and the occurrence of mite bites to humans.
Frequently Asked Questions
- What is causing the red, itchy bites that many people in our area are encountering?
- It is likely an itch mite known as Pyemotes herfsi which feeds on certain insects in trees and then drops to the ground, landing on people on the way, which then bites them.
- It is likely an itch mite known as Pyemotes herfsi which feeds on certain insects in trees and then drops to the ground, landing on people on the way, which then bites them.
- Are the itch mites coming out of periodical cicada egg nests?
- To my knowledge, no one has actually found P. herfsi mites in cicada egg nests in this area. However, given the historical association of the two, it is likely that the abundance of Brood X periodical cicada eggs as potential food for the mites has resulted in an increase in mite densities and the occurrence of mite bites to humans.
- To my knowledge, no one has actually found P. herfsi mites in cicada egg nests in this area. However, given the historical association of the two, it is likely that the abundance of Brood X periodical cicada eggs as potential food for the mites has resulted in an increase in mite densities and the occurrence of mite bites to humans.
- How did I get itch mite bites?
- The most likely exposure is when hiking, walking, sitting, etc. under trees infested with insects that the mites feed on (ex. trees, such as oaks, with periodical cicada egg nests or galls caused by insects)
- Raking or leaf blowing leaves (for mites coming from leaf galling insects)
- Itch mites dropping from trees can be carried by wind and may land on you.
- How do you tell the difference between P. herfsi itch mite and chigger mite bites?
- Itch mite bites usually occur in the upper body around the neck, shoulders, and chest; Chigger bites usually occur in “tight” places on the lower parts of the body like under belt or waste lines, underwear, socks, or other places clothing is tight against skin.
- Itch mite bites usually occur in the upper body around the neck, shoulders, and chest; Chigger bites usually occur in “tight” places on the lower parts of the body like under belt or waste lines, underwear, socks, or other places clothing is tight against skin.
- How long after being bitten do bites start to itch?
- Symptoms start to appear 10-16 hours after exposure.
- Symptoms start to appear 10-16 hours after exposure.
- What do the itch mite bites look like?
- Bites may look like raised, red areas with a small central blister on the skin; the bites are itchy and may be painful if scratched; bites occur on the upper body around the neck, shoulders, and chest.
- Bites may look like raised, red areas with a small central blister on the skin; the bites are itchy and may be painful if scratched; bites occur on the upper body around the neck, shoulders, and chest.
- What can I do for itch mite bites?
- Do NOT scratch as this may lead to secondary bacterial infections
- Use products labeled to provide relief from itching and other symptoms
- Consult a doctor if symptoms are bad or infections appear.
- How can I prevent itch mite bites?
- Reduce exposure to trees with cicada egg nests or galls (ex. oaks).
- Bathe shortly after spending time in areas where you may have been exposed to itch mites.
- Wear protective clothing when in areas of potential exposure or raking / leaf blowing leaves (ex. long sleeves, a hat, gloves).
- Repellents used to prevent bites from mosquitoes, ticks, etc. have not been effective against itch mites.
- Can I apply pesticides to trees with cicada egg nests to kill the itch mites?
- Application of miticide sprays to trees with cicada egg nests are not likely effective since mites are protected from exposure within the cicada egg nests.
- Application of miticide sprays to trees with cicada egg nests are not likely effective since mites are protected from exposure within the cicada egg nests.
- When will the itch mites go away?
- Cicada eggs take 6-10 weeks to hatch. Egg hatch for most Brood X periodical cicada eggs should be completed by the end of August in this area. Once the food source for the itch mite is gone, their densities should go down.
Resources for more detailed information on itch mites (Pyemotes herfsi)
Itch Mite Update, Illinois Dept of Public Health (2008)
http://www.idph.state.il.us/envhealth/pcitchmites_update5-23-08.htm
Oak Leaf Itch Mite by Ray Cloyd (2019)
https://bookstore.ksre.ksu.edu/pubs/MF2806.pdf
Research article: Pyemotes herfsi (Acari: Pyemotidae), a Mite New to North America as the Cause of Bite Outbreaks. J. Med. Entomol. 43(3): 610-613 (2006). https://www.srs.fs.usda.gov/pubs/ja/ja_moser050.pdf
By Paula Shrewsbury, Department of Entomology, University of Maryland
Para leer este posteo en Español, visite esta página: https://extensionesp.umd.edu/2021/08/13/picazon-por-acaros-de-hoja-de-roble-y-su-relacion-con-los-huevos-de-cigarras-periodicas/