Reviewed by William "Willy" Vizcarrondo, NYS DEC Certified Commercial Pesticide Applicator C1825832. Updated September 23, 2026.
Short answer
Spring, on the first warm, sunny days after a soaking rain, most often from late March through May on Long Island. Penn State puts eastern subterranean termite swarms between February and June in Pennsylvania, and UC IPM notes they emerge on warm afternoons following spring rains. A swarm lasts a few hours, and the swarmers you find afterward are dead or wingless within a day.
Warmth and moisture together. A mature subterranean termite colony produces winged reproductives once a year, and they wait underground until conditions are right to fly, pair up and start new colonies. UC IPM describes the trigger plainly: on warm, sunny days following fall or spring rains, swarms of reproductives may be seen emerging en masse, and the eastern subterranean termite in particular flies in the afternoon after a soaking rain. Penn State gives the window in Pennsylvania as February through June, and the middle of that range is what Long Island sees. A stretch of rain followed by a sunny afternoon in the 60s or 70s in April is the classic swarm day.
Hundreds of dark, winged insects at once, then a pile of wings. Penn State describes the winged reproductives as dark brown or black and about 3/8 to 1/2 inch long, with two pairs of equal-length wings. Indoors they come out of a crack at the base of a wall, around a window frame, a door sill or a basement slab joint, fly toward light, and end up on windowsills and in light fixtures. They shed their wings within hours, so what most people find is a scattering of identical clear wings on a sill and a few crawling, wingless swarmers that look like dark ants with thick waists. Outdoors you'll see them coming out of the soil, a stump or a mulch bed in the yard.
Collect a few and call for an inspection. Put some swarmers or wings in a bag or a piece of tape so they can be identified, note exactly where they came out, and vacuum the rest; they can't bite, sting or damage wood, and they die the same day. Then get the house inspected, because University of Kentucky's extension guidance is that winged termites emerging indoors almost always indicate an infestation warranting treatment. Don't spray the swarmers. It does nothing to the colony underground and it makes the evidence harder to read.
Swarm season here runs late March into May, and it comes in waves: one warm day after rain and the phone rings from Levittown, Massapequa and Freeport in the same afternoon, then a week of quiet, then another wave after the next rain. Slab-on-grade houses and finished basements in the postwar Nassau developments produce a lot of indoor swarms because the swarmers come up through expansion joints and around plumbing penetrations. If you saw swarmers in the yard but not in the house, that's worth an inspection too, since the colony is within foraging distance.
Related
Occasionally. UC IPM notes swarms can follow fall rains as well as spring ones, but on Long Island the spring flight is the main event and a fall swarm is uncommon. Winged insects in the house in September are more likely to be ants; check the waist and the wing lengths.
Eastern subterranean termites swarm in daylight, usually in the afternoon. Winged insects around a porch light at night are more likely to be flying ants, which do fly at night, or one of the other insects that come to light. If you found wings in the morning on a windowsill, they may have swarmed during the day while you were out.
Not always, but it means one is close. UC IPM notes that finding swarming termites in your yard doesn't necessarily mean your house has termites, since soil holds buried wood and roots that colonies live on. Swarmers coming out inside the house are a different matter; that almost always means the colony is feeding on the structure.
Still not sure? Call (516) 509-6001 and we'll tell you what you're dealing with.