On a warm, humid day in mid-July, virtually every black garden ant (Lasius niger) colony in the country releases its winged queens and males at the same time. The synchronised swarm — often called flying ant day, though it usually plays out over two or three days — is a mating flight, not an invasion. But it does tell you exactly where the local nests are.
Why they all fly at once
Mass emergence overwhelms predators and gives queens the best chance of meeting males from a different colony. Warm ground temperatures, low wind and high humidity after recent rain are the usual triggers, which is why the date shifts a week or two each year.
Is a swarm in your garden a problem?
- Winged ants coming out of a lawn or border — almost always harmless. The males die within hours and mated queens fly off to start new nests elsewhere.
- Winged ants emerging from an airbrick, doorframe, kitchen skirting or under a conservatory floor — there's an established nest inside or under the building. Treat it.
- Trails of ordinary worker ants leading into the kitchen for weeks before the swarm — same nest, same treatment.
What actually works
Sprays kill the foragers you can see and leave the queen producing replacements within days. A professional gel bait is carried back to the nest by the workers and wipes out the colony, usually within a week. If the swarm came from under a solid floor or a wall cavity, that's the only reliable option.