Black flies in Michigan
Yes — black flies are recorded in Michigan. The GBIF biodiversity database holds 218 verified black fly records from the state — one of the highest counts in the country. Sightings concentrate in May to July. Onset: often painless at first, itch builds over hours. Duration: up to a week, sometimes with lasting swelling.
| Verified records | 218 |
|---|---|
| Peak sightings | May to July |
| State bite season | May to October |
| Active | daylight, worst in late spring near running water |
| Habitat | fast-flowing streams and rivers — larvae need moving water, so they are absent from still ponds |
| Bite appears | often painless at first, itch builds over hours |
Black fly bites in Michigan: what the mark looks like
Black flies cut a small hole and pool blood, so the classic finding is a pinpoint blood spot that later swells and itches intensely. They crawl into hair and under collars, which is why bites cluster at the hairline and behind the ears rather than on open skin.
Locally, the species most often confused with it are mosquito bite, yellow sac spider bite — all of which are also recorded in Michigan.
Seek medical care if
- marked swelling around the eyes
- fever or spreading redness
- breathing difficulty (rare allergic reaction)
What else it could be in Michigan
These are recorded in Michigan too and are the ones most often confused with it here. The differences below are the ones that actually separate them.
| Black fly bite | Mosquito bite | |
|---|---|---|
| Pattern | several, along the hairline, ears and ankles | single bumps scattered over exposed skin |
| Where on body | hairline, behind the ears, ankles | ankles, lower legs, arms |
| Appears | often painless at first, itch builds over hours | within minutes |
| Records here | 218 | 177 |
Black fly season in Michigan specifically
Records in Michigan concentrate in May to July, which is what local sighting data shows rather than a national average — seasonality shifts substantially with latitude. The general bite season in Michigan runs May to October.
Because fast-flowing streams and rivers — larvae need moving water, so they are absent from still ponds, exposure in Michigan 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.
Month by month in Michigan
These are the 218 Michigan records broken out by the month they were recorded — not a national curve redrawn for the state. Records appear in 6 of the 12 months here. The single busiest month is June with 91 records (42% of the state total).
| Month | Records | Share |
|---|---|---|
| April | 1 | <1% |
| May | 35 | 16% |
| June | 91 | 42% |
| July | 76 | 35% |
| August | 13 | 6% |
| September | 1 | <1% |
Counts are observations submitted to GBIF, not bites. They tell you when the animal is out and being noticed in Michigan; they do not tell you how many people were bitten. The thinnest month with any record at all is April (1).
How Michigan compares
Across the 27 states with any black fly records, Michigan ranks 2nd with 218. The state directly above it is Pennsylvania (278). Directly below is Wisconsin (99). The highest count anywhere is Pennsylvania (278).
Inside Michigan itself the picture is different again: of the 16 biting species we track with records here, this one is 9th and accounts for 2% of the 10,073 records logged in the state. A species can be common nationally and marginal in one state, or the reverse — which is the whole reason this page exists separately from the national guide.
Care
- wash, cold pack, antihistamine
- avoid scratching — these bleed and crust easily
Avoiding black flies in Michigan
- fine-mesh head net in black fly season
- cover wrists and ankles
- avoid riverside trails in late spring at peak emergence
Questions
Are there black flies in Michigan?
Yes. Michigan accounts for 218 verified records in GBIF, ranking it 2nd among the 27 states with any records for this species, just behind Pennsylvania (278). Within Michigan it is 9th of the 16 biting species we track here, at 2% of the state's records. Records reflect reporting effort as well as abundance.
When are black flies active in Michigan?
Michigan records peak in May to July. The general bite season in Michigan runs May to October.
What does the bite look like?
a small bleeding point that swells into an itchy lump, red, often with a central blood spot. Several, along the hairline, ears and ankles.
Which month has the most sightings in Michigan?
June, with 91 of the 218 Michigan records (42%). Records appear in 6 of the 12 months here. This counts sightings submitted to GBIF, not bites.
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.
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