Tool
Maine Black Fly Season: Timing and Trip Planning
Roughly Mother’s Day to the Fourth of July, and worse the further north and higher you go. This is when each region is usually in it, and where to go instead.
Black fly season in Maine is a planning consideration for time outdoors, especially in spring and early summer. Dates alone cannot tell you how active flies will be beside a particular stream or trail. Use the seasonal guide as an overview, then prepare for the conditions at your destination.
Where the season is today
No region is inside its typical window today.
| Region | Typical window | Today | Reports |
|---|---|---|---|
| Aroostook and the far northCaribou, Presque Isle, Houlton | May 20 to July 10 | Past | none |
| North Woods, Moosehead and KatahdinGreenville, Millinocket | May 15 to July 5 | Past | none |
| Western mountainsRangeley, Bethel | May 10 to June 30 | Past | none |
| Kennebec Valley and inland MaineAugusta, Waterville, Bangor | May 10 to June 25 | Past | none |
| Downeast and AcadiaBar Harbor, Lubec, Eastport | May 15 to June 25 | Past | none |
| MidcoastCamden, Rockland, Boothbay Harbor | May 15 to June 20 | Past | none |
| Southern coast and PortlandPortland, Ogunquit, Kennebunkport | May 20 to June 15 | Past | none |
- Aroostook and the far north: First to turn and last to be free of flies. Both run about two weeks behind the coast in spring and two weeks ahead of it in autumn.
- North Woods, Moosehead and Katahdin: The classic peak-foliage destination, and the worst place in the state to camp in the first half of June.
- Western mountains: Elevation does the work here. A summit can be past peak while the valley below it is still green.
- Kennebec Valley and inland Maine: The middle of the state in both senses. Reliable mid-October color without the mountain crowds.
- Downeast and Acadia: Acadia peaks noticeably later than the mountains, which is why the park is busy well into October.
- Midcoast: The sea holds the temperature up, so color arrives late and hangs on.
- Southern coast and Portland: Last to turn, and the mildest fly season in the state. A sea breeze keeps the worst of them off the beaches.
Where these dates come from
The windows are long-run typical timing, not a forecast for this year. They move with latitude and elevation, which is why the north and the mountains lead and the southern coast trails by a fortnight.
No field reports have been approved yet, so nothing on this page is a live reading. When observations start arriving they will appear in the reports column, dated and credited, and they will sit beside the typical window rather than replacing it.
Any given year can run one to two weeks either side of these dates. A warm, wet autumn delays color and dulls it; a cold spring pushes the flies later and compresses them.
The season, region by region
One shared axis, so the stagger is visible. It starts inland, in the western mountains and the Kennebec valley, around the tenth of May. It finishes first on the southern coast in the middle of June and last in Aroostook in the second week of July — nearly four weeks between the two, and the reason a June trip is a different proposition depending which way you drive.
When are black flies active in Maine?
Maine’s parks guidance describes a typical season from late April through June, with activity sometimes extending beyond that period. Rainfall, temperature and local wet conditions affect the experience. An end date on a regional calendar should never be read as a promise that the insects disappear that day.
A trip outside the broad spring window can still encounter biting insects. Separate a general seasonal pattern from a recent observation at the place you intend to visit; neither a blank map nor a missing report establishes that an area is fly-free.
Place matters more than a regional cutoff
Black flies develop in running water, and different species use different types of streams. That is a useful distinction when comparing an inland waterside outing with other plans, but it does not produce a dependable start or finish date for an entire county.
Aroostook, the North Woods, the western mountains, the Kennebec area, Down East, the Midcoast and southern Maine cover many local settings. Use these regional names to find your destination. Do not interpret a broad region’s color on a map as a measurement at a campsite, river access or town center.
Prepare for the outing you actually plan
A head net, long sleeves and long pants give you options when insects are persistent. Keep that preparation with the rest of your outdoor gear instead of relying on a calendar to decide whether it will be needed.
For a walk with children, a long pause beside water and a moving hike are different plans. Leave room to shorten an uncomfortable outing or choose another activity. General timing can help organize the trip, while the experience at the trailhead decides how that day unfolds.
Read local reports with their dates
A useful report names a place, an observation date and the conditions seen there. A comment from another season or a broad regional description cannot answer what is happening on your chosen trail today. When no current observation is available, treat local activity as unknown.
For regional trip context, start with the Maine Lakes and Mountains guide. Choose activities for their own interest and access arrangements, without an assurance that any Maine region avoids black flies entirely.
Sources: September 14, 2026 — Maine Bureau of Parks and Lands, University of Maine Cooperative Extension.
Common questions
When is black fly season in Maine?
Roughly Mother's Day to the Fourth of July, worst from the middle of May through the middle of June. It starts earlier inland and in the south, and runs latest in the north and at altitude.
How bad is it really?
Bad enough to change plans in the North Woods in early June. They bite in daylight, they are worst near running water on still, humid days, and a head net is normal equipment rather than an overreaction.
Where can I escape them?
The open coast. A steady sea breeze keeps them down, so the southern beaches and the exposed headlands are the mildest places in the state during the worst weeks.
When do they stop?
The first generation fades as the streams warm and slow. By mid-July the flies are largely done and the mosquitoes have taken over, which is a different problem with the same solution.
