#EntomologyConsult: (rephrased because I don’t provide medical advice via Twitter but am happy to discuss generalities!) Lesion appears in the AM after field work the previous day. How can one determine whether it is a from an bite? https://twitter.com/biologycarly/status/1290645679241658368

T-cells respond to dangerous antigen. It takes awhile (eg 24 hours) for them to really get going but then redness and swelling worsen over days to weeks before subsiding. There are subsets of T-cells that respond to different types of threat. The Th2 subset responds to arthropods

Th2 cells cause itch along with redness and swelling. In contrast, Th17 cells respond to bacterial threats. They cause identical redness and swelling but cause pain instead of itch. There are caveats, but the general rule: itch = Th2 = arthropod bite; pain = Th17 = bacteria

If the lesion itches within 24 hours of exposure, it means that those T-cells have seen the saliva before and were ready to respond. That’s an interesting clue. Mosquitoes, fleas, mites... something common enough to re-encounter.