A swarm that looks like an infestation
Large numbers of winged ants on a patio, in a doorway or around a window can look like a sudden pest problem. This article summarises two UK sources: the Royal Society of Biology (RSB) page on its Flying Ant Survey, which ran from 2012 for three years, and the Natural History Museum (NHM) guide to flying ants. Both describe the United Kingdom as a whole, so the picture applies across England, Wales, Scotland and Northern Ireland, although local weather decides timing. The sources describe the biology of the swarm; they are not treatment guidance, so advice on removing ant nests is covered in How to Stop Ants Getting Into Your Home: A Prevention Guide and Ants Indoors: Why Identification Matters Before Treatment.
What flying ants are
The NHM explains that flying ants are known as alates. In the UK, particularly in urban areas, the winged insects seen are almost always the sexually mature queens and males of the black garden ant, Lasius niger, with the larger ants being queens up to 15 millimetres long. The RSB reports that its survey, using thousands of ants sent in by participants, found that close to 90% of flying ants were of that one species. The NHM notes that red ants (Myrmica rubra) and other species also grow wings, and that in woodland wood ants may be seen.
There is no single “day”
Both organisations address the idea of a national flying ant day. The RSB found that there is not one day on which the ants all appear. Depending on weather, they can start flying at almost any point in the summer months, and the pattern differs between years. It reports that flying ants were spotted on as many as 96% of days between the start of June and the start of September, and that colonies show no significant geographical coordination: one garden may see winged ants on one day and neighbours weeks or even months later. The NHM adds that swarms can appear any time between June and the start of September, that peaks last only a few days, and that ants tend to fly earlier in urban areas than rural ones, probably because of the urban heat island effect. Sometimes the same colony may produce flying ants more than once in a season, according to the RSB.
The weather triggers
The RSB says weather is critical. By comparing sighting records with the nearest weather station data, it found that ants flew only when the temperature was above 13 degrees Celsius and wind speed was under 6.3 metres per second. Every summer day in the study with a mean temperature above 25 degrees Celsius had ants flying somewhere. Ants were also more likely to fly on days that were warmer and less windy than the day before. The NHM similarly says swarming is triggered by weather and adds that there is anecdotal evidence of flying ant days after summer rain, and that timing varies by species.
Why they swarm
An ant colony can expand only so far, the NHM explains, so a new queen must leave and found a colony of her own. She needs to mate with a male from another colony, and wings allow her to disperse. The NHM says that when males and virgin queens scatter, this maximises the chance of mating between different colonies and reduces inbreeding, and that emerging in huge numbers gives protection from predators and improves the chance of finding a mate. It says they are not interested in people or picnics. The RSB describes mating as taking place in flight, with the male dying shortly afterwards.
What happens after the flight
According to both sources, the fertilised queen lands, chews off her wings and looks for a place to start a new colony. The NHM says this is why large wingless ants may be seen walking about after a swarm, and why discarded wings may be scattered over pavements. It states that the queen digs an underground chamber, lays her first eggs and does not eat for weeks until her first daughter workers can forage. Males usually live only a day or two more. The NHM says a queen can live for up to 15 years and large nests can hold more than 20,000 workers.
Where the nests are
The NHM says black garden ants nest in dry soil and are often found in flower beds and lawns and under paving slabs or stones, with patios a favoured location. It notes that heaps of soil may appear above nests in the weeks before a swarm.
Are flying ants useful?
The NHM describes them as beneficial: their tunnelling improves soil, and swarms provide food for birds such as swifts and gulls. It also says the black garden ant and cornfield ant have a mutually beneficial relationship with the silver-studded blue butterfly on heathland. That context matters for anyone weighing whether a short-lived swarm needs any treatment at all.
Questions to ask if ants persist
- Are the ants winged reproductives or wingless workers seen every day?
- Are they coming from soil under a patio or paving, or from inside the structure?
- Is a professional inspection needed to identify the species before any treatment?
The bottom line
Flying ants in the UK are a seasonal, weather-driven event, not a single national day. The RSB survey found that winged ants can be seen on nearly every day between June and early September, and that temperature above 13 degrees Celsius and light winds are the conditions needed. Most are black garden ant queens and males on a mating flight, after which queens shed their wings to found new colonies. Identifying the species and where the ants are coming from is the sensible step before any treatment decision.
Sources
- Royal Society of Biology, “Flying Ant Day” (Flying Ant Survey) (rsb.org.uk)
- Natural History Museum, “Flying ant day: when winged ants take their nuptial flight” (nhm.ac.uk)