Reports are coming from Maryland about people being bitten by a tiny mite that has been associated with the Brood X periodical cicada emergence. The culprit is a non-native “itch mite,” Pyemotes herfsi. Bites from the mite produce pruritic (itchy skin) rashes and the discomfort may last for several days. Thus far, there have been no reports from anywhere in Ohio.
Although the mite is classified as an insect parasite, it behaves more like a vampire in the truest horror-picture sense of the word. The mite first immobilizes its insect victim by using its fang-like mouthparts (chelicerae) to inject saliva containing a paralyzing neurotoxin, and then it drains the victim's hemolymph (insect blood).
This tiny mite has a big bite! The neurotoxin of this mighty mite is powerful allowing it to subdue an insect larva that's 166,000 times its own weight. It is suspected that the neurotoxin is responsible for the “itch mite” designation by playing an important role in producing skin reactions suffered by its people-victims.
Once the mites exhaust their insect-food supply, they may drop from trees in search of nourishment. They become “itch mites” on people who inadvertently intersect the movable feast. Bites most commonly occur beneath shirt collars on the back of the person’s neck.
Mite bites may also occur after handling plant material infested with the insects these mites are attacking. Researchers investigating P. herfsi in association with periodical cicada eggs in Illinois in 2007 reported that they developed pruritic rashes on their hands and arms after handling tree stems with cicada oviposition slits.
P. herfsi is not the first mite in this genus to earn the “itch mite” moniker. In fact, numerous scientific papers detail the development of pruritic rash symptoms on individuals bitten by other Pyemotes mites. Some dermatology guides refer to the condition as “Pyemotes Dermatitis.”
BYGL readers may recognize P. herfsi from past postings connecting the mite with a gall midge, Macrodiplosis erubescens (family Cecidomyiidae). The midge fly produces so-called marginal leaf fold galls on oaks belonging to the red oak group, particularly black (Quercus velutina), red (Q. rubrum), and pin oak (Q. palustris).
A 2006 paper titled, Pyemotes herfsi (Acari: Pyemotidae), a Mite New to North America as the Cause of Bite Outbreaks, [see “Selected References” below] details an investigation into an outbreak of itching bites on football players after they attended a picnic in a park at Pittsburg State University, in Pittsburg, KS, on August 26, 2004. Although the authors reported It was the first time this European “itch mite” had been found in the U.S., other publications dispute the claim.
The investigators demonstrated a clear direct connection between the itch mite and the gall midge M. erubescens found in their leaf fold galls on oaks shading the picnic area. The mites feast on the gall midge maggots but drop from the leaves once their maggoty food supply is exhausted or if the maggots drop from the leaves to pupate in the soil. The connection with the gall midge on oaks is the reason some publications refer to P. herfsi as the “oak leaf itch mite.”
A technical report published in 2008 connected bites from P. herfsi in the Greater Chicago counties of Cook and Du Page in August 2007 with the eggs deposited by Brood XIII 17-year periodical cicadas (Magicicada spp.) in the spring. The report titled, 2007 Outbreak of Human Pruritic Dermatitis in Chicago, Illinois caused by an itch mite, Pyemotes herfsi (Oudemans, 1936) (Acarina: Heterostigmata: Pyemotidae), was compiled and published by the Illinois Natural History Survey and describes some excellent scientific sleuthing. The report includes pictures of cicada eggs that are collapsed and dehydrated owing to the depredations from P. herfsi.
Itchy mite outbreaks have been reported over the years in various other states including Missouri, Nebraska, Oklahoma, Pennsylvania, Tennessee, and Texas as well as Ohio. Some may have related to 17-year or 13-year periodical cicadas, or with the gall midge, or both. Most were anecdotal reports with no published investigations.
Take-Home Message Regarding Mysterious “Bug Bites”
A serious diagnostic challenge is presented when people are bitten by something difficult to detect due to the small size of the culprit coupled with unusual circumstances that bring the victim within reach of the biter. Pyemotes mites fit both conditions.
The mites are extremely small; they are just one step above microscopic. Scientific publications have documented these mites feeding on insect eggs, insects associated with stored grain, moth caterpillars, as well as wood-boring insects including beetles found in cut wood. Making the diagnostic connection between these mite meals, the tiny itch mite, and people developing pruritic rashes requires a leap across several disciplines.
The bottom line is that Pyemotes mites have demonstrated they can produce dramatic outbreaks of pruritic dermatitis. This should cause entomologists, Extension professionals, pest control operators, and others to broaden their scope of inquiry when confronted with complaints of “bug bites” produced by a mysterious, unseen culprit.
1910. Webster, F. M. A Predaceous and Supposedly Beneficial Mite. Pediculoides, Becomes Noxious to Man. Ann. Ent. Soc. Am. 3: 15. https://doi.org/10.1093/aesa/3.1.15
1952 Booth B. H., R.W. Jones. Epidemiological and Clinical Study of Grain Itch. JAMA. 1952;150(16):1575–1579. doi:10.1001/jama.1952.03680160025006
1979. Samsinák, K., J. Chmela, and E. Vobrázková. Pyemotes herfsi (Oudemans, 1936) as causative agent of another mass dermatitis in Europe (Acari, Pyemotidae). Folia Parasitologica. 26(1):51-54. PMID: 156143.
1988. Tomalski, M., W. Bruce, J. Travis, and M. Blum, M. Preliminary characterization of toxins from the straw itch mite, Pyemotes tritici, which induce paralysis in the larvae of a moth. Toxicon, 26(2), 127-132. doi:10.1016/0041-0101(88)90164-X
2006. Broce, A.B., L. Zurek, J.A. Kalisch, R. Brown, D.L. Keith, D. Gordon, J. Goedeke, C. Welbourn, J. Moser, R. Ochoa, E. Azziz-Baumgartner, F. Yip, and J. Weber. Pyemotes herfsi (Acari: Pyemotidae), a Mite New to North America as the Cause of Bite Outbreaks, Journal of Medical Entomology, Volume 43, Issue 3, Pages 610–613. doi: 10.1603/0022-2585(2006)43[610:phapam]2.0.co;2. PMID: 16739423.
2007. Alberto B. B., and J. Kalisch. Pests That Affect Human Health – Oak Itch Mite. Kansas State University Fact Sheet, MF-2806, pp 2. https://web.archive.org/web/20110716115233/http://www.ksre.ksu.edu/library/entml2/mf2806.pdf
2008. Zaborski, E. R. 2007 Outbreak of Human Pruritic Dermatitis in Chicago, Illinois caused by and itch mite, Pyemotes herfsi (Oudemans, 1936) (Acarina: Heterostigmata: Pyemotidae). Illinois Nat. Hist. Surv. INHS Technical Report 2008(17). http://hdl.handle.net/2142/18171
2008. S.E. Glosner. Pyemotes: the mysterious itch mite. US Pharm, 33 (5) (2008), pp. 59-64
2011. Sceppa, J. A., Y.H. Lee, S.B. Jacobs, and D.R. Adams. What's eating you? Oak leaf itch mite (Pyemotes herfsi)[BJ1] . Cutis, 88(3), 114-116. https://pubmed.ncbi.nlm.nih.gov/22017061/