Deer fly bites in Illinois
Illinois has 59 verified deer fly records in the GBIF biodiversity database — ranking it 9th nationally. Sightings concentrate in June to July. The bite itself appears immediate sharp pain and lasts a few days.
| Verified records | 59 |
|---|---|
| Peak sightings | June to July |
| State bite season | April to October |
| Active | daylight hours, worst in humid weather near water |
| Habitat | wetlands, lakesides, wooded trails |
| Bite appears | immediate sharp pain |
Identifying it in Illinois
Deer flies circle the head and bite the scalp and neck, which distinguishes them from horseflies going for legs and back. The patterned wings and gold-green eyes are visible when one lands.
Locally, the species most often confused with it are mosquito bite, honey bee sting, bald-faced hornet sting — all of which are also recorded in Illinois.
Seek medical care if
- spreading redness and warmth
- fever with swollen glands after a bite
What else it could be in Illinois
These are recorded in Illinois too and are the ones most often confused with it here. The differences below are the ones that actually separate them.
| Deer fly bite | Horsefly bite | Black fly bite | |
|---|---|---|---|
| Pattern | single or a few, often on the scalp and neck | single, occasionally two | several, along the hairline, ears and ankles |
| Where on body | scalp, neck, shoulders — they target the highest point of a moving person | legs, back, shoulders — often through thin clothing | hairline, behind the ears, ankles |
| Appears | immediate sharp pain | immediate, sharp — you feel this one | often painless at first, itch builds over hours |
| Records here | 59 | 206 | 44 |
Season in Illinois specifically
Records in Illinois concentrate in June to July, which is what local sighting data shows rather than a national average — seasonality shifts substantially with latitude. The general bite season in Illinois runs April to October.
Because wetlands, lakesides, wooded trails, exposure in Illinois tends to be concentrated in specific places rather than spread evenly — which is why a bite history ("where were you in the 24 hours before?") narrows the answer faster than the appearance of the mark.
Care
- wash, cold pack, antihistamine
- keep the site clean
Avoiding them in Illinois
- hats and light-coloured clothing
- sticky patches on caps work surprisingly well on trails
- repellent has limited effect
Questions
When are deer flys active in Illinois?
Illinois records peak in June to July. The general bite season in Illinois runs April to October.
Are they common in Illinois?
Illinois accounts for 59 verified records in GBIF, ranking it 9th among states for this species. Records reflect reporting effort as well as abundance.
What does the bite look like?
a painful red weal, smaller than a horsefly bite, red. Single or a few, often on the scalp and neck.
Get a photo assessment in the app
Everything above is free to read. The app adds what a page cannot: point your camera at the bite and get an assessment of the most likely cause, a severity read, and a day-by-day care plan — including the specific signs that mean you should be seen.
iPhone and iPad. Free to download.