In 2021, I posted a BYGL Alert titled, “Itchy Alert” (August 9, 2021) regarding a possible connection between periodical cicadas (Magicicada spp.) and outbreaks of the non-native parasitic “itch mite,” Pyemotes herfsi (family Pyemotidae). The Alert referenced reports from Maryland of itchy outbreaks associated with Brood X (10) of the 17-year cicadas. You can read the Alert by clicking on this hyperlink:
https://bygl.osu.edu/node/1842
BYGL readers may recognize P. herfsi from past Alerts 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). Consequently, it’s commonly referred to as the Oak Gall Midge.
Margial Leaf Fold Galls – Midge Fly (Macrodiplosis erubescens) 1
Margial Leaf Fold Galls – Midge Fly (Macrodiplosis erubescens) 2
Oak Gall Midge (Macrodiplosis erubescens) – Maggots in Leaf Fold Gall
The mite behaves more like a tiny vampire. It first immobilizes its insect victim by using its fang-like mouthparts (chelicerae) to inject saliva containing a paralyzing neurotoxin. Then, in vampire style, 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 weight, including the larvae (maggots) of the oak gall midge. They become menacing “itch mites” when they exhaust their insect-food supply and drop from trees in search of nourishment.
If they drop onto people, they may use their chelicerae to deliver a bite. It’s suspected that the neurotoxin injected with their bite is responsible for the “itch mite” designation by playing an important role in producing skin reactions suffered by its people-victims.
The bites have been described as producing small, circular, rosy-red, pruritic (itchy skin) rashes and the discomfort may last for several days. Since the mites drop from trees, most of the bites occur on a person’s arms and upper body particularly beneath shirt colors on the back of a person’s neck.
P. herfsi is not the first mite in this genus to earn the “itch mite” moniker. 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.”
P. herfsi is believed to be native to Europe where it was first described in 1936. In fact, there are reports from Europe of the mite being directly associated with mysterious occurrences of “insect bites.”
The mite has found its way to North America, with the connection to midge maggots in leaf fold galls first observed in 2004 in Pittsburg, KS. Since that time, itchy mite outbreaks have been reported in Chicago as well as various locations in Missouri, Nebraska, Oklahoma, Pennsylvania, Tennessee, and Texas. In 2008, I received a phone call from the Hamilton County (Ohio) Health Department about reports of bites occurring to bikers along a bike trail just east of Cincinnati.
A technical report published in 2008 connected bites from P. herfsi in the Greater Chicago area in August 2007 with the eggs deposited by Brood XIII of the 17-year periodical cicadas. The comprehensive report was compiled and published by the Illinois Natural History Survey in response to a request from the Illinois Department of Public Health for help in identifying a mysterious outbreak of “insect bites” in Cook and DuPage Counties.
The report describes some fascinating scientific sleuthing and includes pictures of cicada eggs that are collapsed and dehydrated owing to the depredations of P. herfsi. Also, the report noted that mite bites may occur after handling plant material infested with the insects these mites are attacking. The researchers investigating noted that they developed pruritic rashes on their hands and arms after handling tree stems with cicada oviposition slits.
Periodical Cicada Eggs in Oak Stem
Aside from the report from Maryland referenced at the beginning of this Alert, Brood X (10) of the 17-year periodical cicadas also generated a media report of an outbreak of “oak leaf gall mites” that was linked to the cicadas in the Miami [River] Valley, Ohio. The report was made in September 2021 by a Dayton television station and noted that a dermatologist in the area was seeing two or three patients a day with mite-bite symptoms.
Putting the Mite Before the Bite
As demonstrated with the midge maggots in the oak leaf fold galls, P. herfsi is not just associated with periodical cicadas. People aren’t being attacked by hangry mites that only get fed every 13 or 17 years.
The mites will feed on a wide variety of arthropod prey found in trees. Indeed, in Europe, pyemotid mites will chow down on a wide range of tree-dwelling insects including scales. So, they are already in the trees when the pearly-white periodical cicada egg banquet arrives.
The cicada eggs remain in tree stems and are available to the mites for 6 to 10 weeks. Each cicada “egg-nest” may contain 20–30 eggs, and a female cicada may lay 400 to 600 eggs in her lifetime. Of course, the sheer volume of cicada egg meat morsels would certainly be a boon for mite reproduction.
Periodical Cicada Eggs in Maple Stem (New Growth)
However, the cicada meat market eventually closes once the cicada eggs hatch, and the nymphs drop to the ground. The proliferated mites are then left behind searching for food. This is when they bail from the trees to possibly descend upon unsuspecting hikers, bikers, and others enjoying the great outdoors. The bottom line is that the mites don’t bail until after the cicada nymphs bail which is why mite bite reports usually don’t occur until late in the growing season.
Take-Home Message Regarding Mysterious “Bug Bites”
"Just because you're paranoid, doesn't mean they aren't out to get you."
Joseph Heller in Catch-22.
Complaints of people being bitten by something that’s difficult to detect presents a serious diagnostic challenge. This is particularly true when the culprit is one step above microscopic and the circumstances that bring the victim within reach of the biter are unusual. Pyemotes mites fit both conditions.
I’m not suggesting that this year’s periodical cicada emergence will necessarily produce itchy mite outbreaks in Ohio or elsewhere. If fact, such occurrences appear to be extremely rare. However, the possibility should be considered when people are complaining about mysterious “bug bites.”
Entomologists, Extension professionals, pest control operators, and others should broaden their scope of inquiry when confronted with such complaints. It’s important to consider the time of the year as well as whether the person lives in a location or has visited an area where periodical cicadas have emerged en masse during the spring.
Selected References
Borchers, C. E., Schaetzle, T., & Borchers, S. (2022, October 1). Pyemotes herfsi Dermatitis: A Case of 17 Year Itch (Poster Presentation). Wright State University, Dermatology Faculty Publications, Dayton, OH, United States
https://corescholar.libraries.wright.edu/dermatology/15/
Broce, A. B., Zurek, L., Kalisch, J. A., Brown, R., Keith, D. L., Gordon, D., ... & Weber, J. (2006). Pyemotes herfsi (Acari: Pyemotidae), a mite new to North America as the cause of bite outbreaks. Journal of medical entomology, 43(3), 610-613.
https://doi.org/10.1093/jmedent/43.3.610
Glosner, S. E., & Kang, E. (2008). Pyemotes, the Mysterious Itch Mite. US PHARMACIST, 33(5), 59.
https://www-staging.uspharmacist.com/article/pyemotes-the-mysterious-itch-mite
Karban, R. (1984). Opposite density effects of nymphal and adult mortality for periodical cicadas. Ecology, 65(5), 1656–1661.
https://doi.org/10.2307/1939144
Koweek, M. (2021, September 13). MIAMI VALLEY — A new bug outbreak is causing trouble in the Miami Valley: oak leaf gall mites. Live Local News. broadcast, Dayton, OH; WHIOTV7.
Samsinak, K., Chmela, J., & Vobrazkova, E. (1979). Pyemotes herfsi (Oudemans, 1936) as causative agent of another mass dermatitis in Europe (Acari, Pyemotidae). Folia Parasitologica, 26(1), 51-54.
https://europepmc.org/article/med/156143
Vargas, S. 2021. Cicadas may be gone, but here come itch mites causing mysterious bites in Washington, DC, region. USA Today: Nation, 4 August 2021. https://www.usatoday.com/story/news/nation/2021/08/03/pyemotes-oak-tree-itch-mites-cicada-washington-dc-region/5478360001/
Zaborski, E. R. (2008). 2007 Outbreak of Human Pruritic Dermatitis in Chicago, Illinois Caused by an Itch Mite, Pyemotes herfsi (Oudemans, 1936) (Acarina: Heterostigmata: Pyemotidae). Technical Report INHS 2008 (17).
https://www.ideals.illinois.edu/items/18258