Every summer, normally in July or August, huge numbers of male worker ants and young queen ants will suddenly develop wings.
The day when the most flying ant sightings take place has been dubbed Flying Ant Day, even though not all ants will fly on the same day.
The flying ant period can last up to a few weeks, depending the location of the ants, species, local weather and a number of other factors.
Professor Adam Hart, from the University of Gloucestershire, said that there is "no such thing as Flying Ant Day” and the winged insects "will be picking up across the country” in coming months.
The insert expert said that flying ants usually take off around the third week of July but they seem to have appeared early in the capital, with many sightings in London this afternoon.
Professor Hart said Londoners will probably see more flying ants from around 4pm, adding: "There seem to be lots of ants in London at the moment. Probably because of the recent heatwave.”
What happens on Flying Ant day? Why do ants grow wings?
In the UK, it is the small black garden ant, Lasius niger (Formicidae), that will take to the sky.
Their nests have a single queen and typically about 5,000 workers, although there can be as many as 15,000.
New queens will fly away each year to mate with winger male ants and start a new colony of their own.
The ants will mate mid-air in a nuptial flight before queens lose their wings and land on the ground to start a new colony.
Disgusting swarm of black flying ants covers wall
After Flying Ant Day, you can sometimes see large queen ants walking around, looking for somewhere to nest.
The queen ants will likely mate with several males during the nuptial flight period.
They can store sperm in their abdomen for a lifetime after the mating period and can use it to fertilise millions of eggs.
The male worker ants will only live for a day or two after the nuptial flights.
David Cross, head of the technical training academy at Rentokil Pest Control, said: "The past few weeks have been on the whole, very warm, which could explain why some areas have seen a sudden increase in ant populations.
"It is common for both male and female garden ants to fly at this time of year in order to mate. Female ants (Queens) and the smaller males (Drones) mate in the air, often in their thousands.
"After the mating has taken place, the Queen ants will find a new landing spot where they’ll bite off their wings and hibernate for the winter – laying the foundations for a nest the following year.
"Once the Queen ants have been fertilised, there is not a great deal that you can do to prevent the foundations of a colony.
"Nevertheless, it’s still advisable to ensure that all foods are sealed, and that any rubbish is properly packaged and placed in closed bins.
“If you are unsure of how to deal with an ant infestation then make sure you call the experts for advice, they will know what products are best to use.”