The Illinois Department of Public Health (IDPH) continues to work diligently to identify the species of the Pyemotes itch mite that caused a rash of bites in northeastern Illinois this August. IDPH is working with Dr. Ed Zaborski, an Illinois Natural History Survey entomologist specializing in mites, to determine the exact species of mite. The genus is confirmed to be Pyemotes, a group known to cause dermatitis in humans. Pyemotes mites are parasites of insects living in protected locations; biting of humans is incidental.

In this group of mites, only males can be identified to species and males make up a very small portion of the population. Originally the mite was suspected to be the oak leaf gall itch mite, Pyemotes herfsi. Currently, specimens are being sent to second specialist for independent verification.

Because it has been difficult to find oak leaves with midge galls, and reports of bites and rashes were coming from neighborhoods that had few, if any, oak trees, the mites may have built their population on a food source other than oak gall midges. Additionally, during the 2004 Kansas outbreak, most oak leaves had midge galls on them, whereas in Chicago, far fewer oak leaves had midge galls.

It is a good possibility the rash of bites is associated with the emergence earlier this year of the 17-year periodical cicada. So far, Pyemotes mites have only been found on cicada eggs in northeastern Illinois this summer. Cicadas lay their eggs in “egg nests” in tree branches, which provide a sheltered environment needed for the mites to multiply.

The emergence of the periodical cicada, only occurring every 17 years, would explain why numerous people have not experienced this type of bite or rash in recent years, but why it is so prevalent this year. And assuming the cicada eggs are the mite host, we would not expect a recurrence of mites next year unless the mites find another suitable and abundant host.