Flying ant day is not a day, and you do not need to buy anything
The largest study ever done on this found flying ants on as many as 96% of days between June and September. There is no single date, there is nothing to treat, and the swarm in your garden is over before anything you order could arrive.
By The Pest GuyLast updated
The short answer
It is a mating flight. It ends by itself.
What you are watching is a nuptial flight. Winged queens and males of the black garden ant leave the nest to mate, and the whole thing exists so that new queens can start colonies somewhere other than where they hatched. The Natural History Museum sums up the intent: they "aren't interested in people or picnics, they're just looking for a mate".
It has a biological ending built in. The males live only a day or two after the flight. The mated queens chew their own wings off and go underground. There is nothing left to treat within days, which is why the Royal Society of Biology's advice is simply that they "are not harmful, so if some emerge in your garden or elsewhere it's best to leave them alone".
The one thing this page will not give you is a date, because the research is that there is not one.
Why there is no flying ant day
The Royal Society of Biology ran a citizen survey starting in 2012 and continuing for three years. The resulting paper, by Hart, Hesselberg, Nesbit and Goodenough in Ecography, describes "the largest ever dataset (>13,000 observations) on the location and timing of winged ant sightings over a three-year period across a broad spatial scale".
What it found breaks the story everyone tells. Observations ran from June to September, with 97% in July and August, "but exact temporal patterns differed substantially between years". More importantly: "the predicted spatiotemporal synchrony was far less apparent; observations were not significantly spatially clustered at national, regional or local scales."
The Royal Society of Biology puts the same finding in plain words. "There is not actually one day where these ants all appear all at once." Instead, flying ants were spotted on as many as 96% of days between the start of June and the start of September.
So the annual headline naming a date is not reporting a fact, it is repeating a habit. The Natural History Museum, citing the same project, calls flying ant day "a misconception" and describes a flying ant season instead, in which winged ants emerge over several weeks with peaks that each last only a few days, and a pattern that varies year to year.
What is true is that it feels like a day where you are standing. Your garden and the one next door will often go up together, because they are experiencing the same weather. That local coincidence is what the whole myth is built on.
What actually sets it off
Three weather numbers, and one of them is the reason your street goes and the next town does not.
The study measured it. Winged ants were "only observed at temperatures >13 °C and wind-speeds <6.3 m-1", and barometric pressure, despite the folklore, was not a significant predictor. Temperature drove flights up, wind drove them down.
The heat threshold is the striking one. "All days with a mean daily temperature >25°C had observations." On a properly hot day in a British summer, ants are flying somewhere in the country, without exception across three years of data.
Then the part that reads as almost deliberate on the ants' side: changes in temperature and wind speed from the day before a flight peak were also significant. The authors conclude that ants "appear able to determine, at least in a limited way, if weather is improving or deteriorating and adjust their behaviour accordingly". They are not waiting for a date. They are waiting for a good day that follows a worse one.
Two more findings explain the pattern on your street. Nests in urban areas, and nests against heat-retaining structures, produced winged ants earlier. The Natural History Museum attributes the same effect to the urban heat island. A nest under a south-facing patio slab in a city goes before one in a rural lawn, which is exactly why "flying ant day" never arrives everywhere at once.
The conclusion the paper draws is the one to take away: "Local weather conditions rather than broad geographical or seasonal factors were shown to be critical in the timing of winged ant activity."
They are the ants you already had
Close to nine in ten of the winged ants recorded by the survey were one species, the black garden ant Lasius niger. The paper puts it at 88.5%. These are the same ants that were under your paving all year, in a life stage they only reach when the colony is ready to reproduce.
The Natural History Museum describes the caste split: the queen lays, female workers do everything else, and "most of the eggs develop into workers, but when the colony is ready, the queen begins to produce virgin queens and males". The winged ants you see are those queens and males. The queens are the large ones, up to 15mm. The ants you see the rest of the year are workers.
Black garden ants nest in dry soil, in flower beds and lawns, and under paving slabs and stones. Patios are a favourite. If you want a warning, there is one: heaps of soil appearing above the nests in the few weeks before it happens.
Afterwards you get the second act that confuses people. Large ants walking about with no wings, and discarded wings scattered on the pavement. Those are mated queens looking for somewhere to dig. One will excavate a chamber, lay her first eggs, and not eat for weeks until her first daughters can forage for her. If she succeeds, that colony can eventually run to more than 20,000 workers and she may live fifteen years.
Which is the honest caveat on this page. A nuptial flight is a two-day event and needs nothing from you. Black garden ants trailing across a kitchen worktop in June are the same species with a different problem, an ongoing one about food and a way in, and this page does not solve it. Do not let a firm sell you a treatment for one by pointing at the other.
The verdict, which is to spend nothing
This is the rare case where the honest answer costs the reader nothing at all.
Shut the windows and doors on the side the swarm is on, for an afternoon. Bring the washing in. Sweep the wings up the following day. That is the entire list.
A powder or a spray bought on the day of a flight arrives too late by design. The swarming is already happening, the males are on a clock measured in days, and the queens have scattered. Whatever you treat, you are treating the tail end of an event that was going to stop anyway. And HSE is clear that "it is an offence not to follow the statutory conditions of use" of a pesticide, so a product used somewhere its label does not cover is a legal problem as well as a wasted tenner.
It is worth saying what the flight is doing while it inconveniences you. The Natural History Museum notes that ants' tunnelling improves soil quality, and that swarming events are a significant food resource for birds, with swifts and gulls feeding on rising swarms. The black garden ant also matters to the survival of the silver-studded blue butterfly on heathland.
None of that obliges you to enjoy it. It does mean that the correct response to a garden full of flying ants in July is to go indoors for a couple of hours, and that anyone quoting you for it is charging you for the weather.
About this resource
The dataset, the weather thresholds, the species share and the finding that flights are not spatially clustered come from Hart, Hesselberg, Nesbit and Goodenough, "The spatial distribution and environmental triggers of ant mating flights: using citizen-science data to reveal national patterns", Ecography 41(6), 2018. The plain-English summary and the advice to leave them alone come from the Royal Society of Biology, which ran the survey. The biology of the flight, the caste system, the queens after mating and the ecological value come from the Natural History Museum. The pesticide label rule is HSE's.
Two honest limits, both deliberate. This page gives no date, because the research says there is not one to give. And it does not tell you whether a flying ant can bite you: it is the single most searched question on the subject, and no source I would put my name to states it either way, so the answer here is that they are not harmful and are best left alone, and no further than that. I do no work and take no referral fee, which is why a page on a 47,000-a-month search term can end with a recommendation to buy nothing.
Common questions
When is flying ant day?
There is not one, and that is the finding rather than a dodge. The Royal Society of Biology survey concluded "there is not actually one day where these ants all appear all at once", and found flying ants on as many as 96% of days between the start of June and the start of September. The peer-reviewed paper behind it recorded flights from June to September, with 97% in July and August, and no significant clustering at national, regional or local scale.
Are flying ants the same as normal ants?
Yes, same species, different life stage. The winged insects are the sexually mature queens and males of the black garden ant, Lasius niger, leaving to mate. The Natural History Museum notes that the ants you see the rest of the year are female workers. So this is not an invasion of something new. It is the ants that were already under the patio, doing the one thing they grow wings for.
Are flying ants dangerous?
The Royal Society of Biology says: "Flying ants are not harmful, so if some emerge in your garden or elsewhere it's best to leave them alone." The Natural History Museum adds that they "aren't interested in people or picnics, they're just looking for a mate". On whether they can bite, none of the sources I would trust on this states it either way, so I am not going to make a claim about it.
How do I get rid of flying ants?
You wait. The flight is a mating event with a hard biological ending: the males live only a day or two afterwards, and the queens chew their own wings off and go underground to start a colony. Nothing you spray shortens that meaningfully, and the swarm you can see is over long before a treatment would be. This is the rare pest question where the correct spend is zero.
Why do they all appear at once?
Local weather, not a calendar. The Ecography study found winged ants only at temperatures above 13°C and wind speeds below 6.3 metres per second, and that every day of the study with a mean temperature above 25°C had ants flying somewhere. It also found that the change in temperature and wind from the previous day mattered, which suggests the ants can tell whether conditions are improving. Nests in urban areas and against heat-retaining structures flew earlier.
What are all the big ants walking around afterwards?
Newly mated queens. The Natural History Museum describes it: "The mated queens quickly chew off their own wings and begin looking for a suitable site in which to nest and set up a new colony." The discarded wings on the pavement are from the same event. A queen will then dig a chamber, lay her first eggs and not eat for weeks until her first workers can forage for her.