A mite. Or mite not. The oak leaf itch mite.
Found in Europe and the Central US. Thousands can get the bite in outbreaks, often spreading to docs who examine the patient. The mite larvae live in leaf galls on pin oak trees. Outbreaks can affect thousands.
Humans get itching from mite bites 10 to 16 hours after contact. The rash is a red patch with a small blister in the center, often multiple. They can look like a comet (PubMed).
Last Update: 04/04/18.