Every year, on some warm, still afternoon in July, it happens. Ants that spent the whole summer as small, ignorable garden furniture suddenly sprout wings and pour out of pavement cracks, patio joints and lawn edges in their thousands. Social media agrees, in near-perfect unison, that today is Flying Ant Day. Somewhere, a gull is having the best afternoon of its year.
Here's the thing: there's no such day. Not officially, not biologically, not really at all.
A citizen science project run by the Royal Society of Biology, drawing on more than 13,000 observations submitted by the public over several years, found winged ants flying on as many as 96% of days between the start of June and the start of September. That's not a day. That's most of the summer. What actually exists is a flying ant season, made up of many local, short-lived pulses, each one triggered independently by weather rather than any shared calendar.
"It isn't one synchronised swarm crossing the country. It's thousands of separate colonies, all reading the same afternoon's weather and reaching the same conclusion at once."
Why it happens at all
What you're watching is a nuptial flight, the one and only occasion in an ant colony's year when its future queens leave home. A mature colony spends the summer raising winged individuals called alates, virgin queens and the males that exist purely to mate with them. When conditions are right, they take to the air together, and it's genuinely a once-in-a-lifetime event for every ant involved.
The logic is straightforward once you see it. A young queen needs to mate with a male from a different colony, not her own siblings, and then find fresh, unclaimed ground to start a nest of her own. Flying solves both problems at once: it lets her range further than she could on foot, and it puts her in the air alongside males from colonies streets away rather than the one under her own doorstep.
Numbers do the rest of the work. A single ant in the open is an easy meal for a bird. Ten thousand ants in the open, all at once, overwhelm every predator in range long enough for a good proportion to survive, mate, and get on with founding the next generation. It's the same mathematics as a bait ball of fish, just with slightly less choreography.
The large winged one is the queen. She's the only one in this whole spectacle who gets to do it more than once, and even she only mates on this single flight.
The weather it's actually waiting for
If it feels like everyone's garden erupts on the same afternoon, that's not coincidence, it's meteorology. Research into the conditions ants fly in found a fairly narrow window: warm (generally above 22 to 24°C), low wind (under about 6.3 metres per second), high humidity, and, ideally, some recent rain. Crucially, the flight tends to follow a day that was an improvement on the one before it.
Put plainly: the classic trigger is a muggy, still afternoon arriving straight after a spell of summer rain. That specific combination doesn't turn up often, but when it does, it tends to sit over an entire region at once, which is exactly why thousands of unrelated colonies across a whole city can look, from the outside, like they organised it together. They didn't. They just checked the same forecast.
This is also why a second, or even third, "flying ant day" a fortnight later isn't a rerun or a mistake. It's a different weather window catching a different set of colonies that weren't quite ready the first time.
- On 18 July 2020, Met Office radar over London and the South East picked up a signal dense enough to be logged as rainfall. It was flying ants.
- The Natural History Museum and BBC News have both documented flying ant swarms appearing on UK weather radar as rain-shaped blooms, large enough and dense enough to register as precipitation to the instruments.
- If you've ever seen a "phantom" rain patch on a weather app that never actually rained where you were standing, mid-summer, warm and still, this is a genuine possible explanation.
The drunk seagull story, honestly assessed
No piece on this subject would be complete without the seagulls, so here's the fair version rather than the fun one.
The popular explanation is that gulls gorge on flying ants and end up visibly drunk, stumbling around and flying erratically, supposedly from the formic acid ants produce as a defence chemical. It's a brilliant story, and it gets repeated every July. It's also, on the evidence, probably not true. Lasius niger, the black garden ant responsible for the overwhelming majority of UK swarms, produces very little formic acid, not enough to plausibly intoxicate a bird the size of a herring gull. The more likely explanation, offered by the RSPB, is simpler and less exciting: gulls gorging on an easy, abundant meal get distracted and overexcited, wandering into roads and traffic because their attention is entirely on feeding, not because they're chemically impaired.
Worth knowing, and worth repeating honestly rather than passing on as settled fact. File it under good folklore, not quite good science.
Things that don't come up much
- A queen mates just once, on this single flight, but stores the sperm for the rest of her life, sometimes 15 to 20 years, using it to fertilise tens of millions of eggs over her lifetime without ever mating again.
- Males exist for almost no other reason than this flight. Most die within a day or two of mating, having done the only thing their body was built to do.
- A mature black garden ant colony can hold more than 20,000 worker ants, all of them daughters of that same, single, once-mated queen.
- Newly mated queens land, then physically chew or shed their own wings off, since they'll never fly again once a nest is underway.
- The whole event you're watching, wings and all, is the ant equivalent of a single, once-in-a-lifetime wedding day, for every individual involved.
When it's a nuisance, and when it's actually a problem
Outdoors, in a garden or on a pavement, this is entirely normal and needs no response beyond closing a window if it bothers you. UK flying ants overwhelmingly don't sting or bite, and the swarm itself is usually finished within a few hours. Let it pass, the same way you'd wait out a heavy shower.
The one distinction actually worth making: ants swarming outside your home are just doing what every colony in the area is doing. Ants emerging indoors, from skirting boards, floor gaps, or window frames, are a different signal entirely, that usually means a mature colony is already living inside the structure of the building itself, not just visiting from the garden. That's the point where it moves from "seasonal event" to "worth getting looked at".
- Swarming outside, in the garden or on paving: normal, seasonal, harmless. No action needed.
- A few winged ants indoors near a window: usually just strays drawn in by light. Open a window, let them find their way out.
- Winged ants emerging from skirting boards, floors, or wall cavities: worth investigating. That's a nest in the structure, not a visit from outside.
A day that was never a day
There's something quietly satisfying about a piece of shared British folklore turning out to be, on closer inspection, not quite what everyone thinks. Not a single day. Not really about the ants "invading". Not, probably, drunk seagulls either. Just thousands of ordinary garden colonies, all independently reading the same warm, still, post-rain afternoon and deciding, all on their own, that today's the day.
Next time it happens, and it will, more than once this summer, it's worth a minute on the doorstep watching it rather than reaching straight for the door. It's the only day any of those ants ever get.
The Quieter Field Notes go out on the first of every month. Each edition covers what's worth noticing outside that month. If this was useful, the newsletter contains monthly things to see and do. Sign up at quieter.life. You'll get 10% off our range as well.
