What a swarm actually is
In Fresno the phone calls come in two waves: late October, after the first real rain, and the tail end of summer, when afternoons sit triple-digit and dead still. Both waves are swarms — a mature termite colony sending out winged reproductives, called swarmers or alates, to pair off and found new colonies. It’s the only moment in a termite’s life cycle when it flies, and the only one most people ever witness.
The key fact: swarming is not an arrival, it’s a departure. Colonies don’t swarm until they’re several years old and well established, so a swarm coming out of your house means the colony has been in it for years already. Even a swarm in the yard means a producing colony within a short flight, working someone’s wood, possibly a fence line, possibly your neighbor’s garage, possibly yours. That’s why swarmers rank near the top of the signs worth acting on, and why the right response is a free inspection rather than a can of spray. The swarm is loud, brief, and harmless in itself; the colony that produced it is the quiet, permanent thing worth finding.
The Fresno swarm calendar
- 1
First fall rains (October–November)
Subterranean swarmers pour out of damp soil on the first warm day after a soaking rain, the biggest flights of the year.
- 2
Warm spring days (March–May)
A second, smaller subterranean window after spring rains, often in the morning.
- 3
Hot, still afternoons (August–October)
Drywood swarmers fly in the heat of the day, in smaller, quieter numbers.
- 4
The rest of the year
Established colonies keep feeding; swarming is the visible event, not the activity.
Who flies when, and how to be sure it’s termites
The two local species keep different calendars because different triggers release them. Western subterranean termites wait for the ground to soften: the first soaking fall rains, followed by a warm, calm day, produce the year’s biggest flights, with a smaller spring window after winter storms. The colony is in the soil, so the whole neighborhood tends to fly at once, and for a week or two wings show up on windowsills all over town. Western drywood termites answer to heat instead. Their swarmers emerge from infested wood on hot, still afternoons in late summer and early fall, in smaller numbers, often one house at a time.
Before acting on either, rule out the great impostor: flying ants, which also swarm after rain. The check takes ten seconds. Termite swarmers have a thick, straight waist, four identical wings about twice the body’s length, and straight, beaded antennae. Ants are pinched at the waist, carry mismatched front and rear wings, and their antennae have an elbow bend. Wings alone are enough: identical and oversized means termites, two sizes means ants.
Which termite it is matters as much as whether it’s a termite at all, since the species decides where treatment happens. When the swarmers themselves are gone, the species guide’s evidence comparison settles it from what they left behind.
Swarmers indoors? Schedule the free inspection while the evidence is fresh.
If they’re swarming right now
Don’t spray. It feels productive and it destroys information: the swarmers die on their own within a day anyway (they’re fragile, half-blind fliers, and nearly all of them fail), while an inspector could have used them to identify the species on sight. Instead, collect a few in a zip-top bag or take a sharp photo, and note precisely where they emerged. A stream coming from a baseboard gap, a window frame, or a garage wall pinpoints the colony in a way that scattered wings never will.
Then close the loop while the evidence is fresh. Vacuum up the rest if you like, but leave the emergence point untouched and book the inspection. Swarm evidence plus an intact emergence site is the easy version of termite diagnosis; the hard version is the same house six months later, with the wings swept away and the colony still eating.