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Page last updated at 11:44 GMT, Friday, 25 July 2008 12:44 UK

Why are there so many flying ants?

The Magazine answers...

Flying ants engage in their airborne mating ritual once a year

Swarms of flying ants have descended upon some parts of the UK over the past few days, only to disappear just as suddenly. Why?

Over the past few days, the phrase "ants in your pants" could be taken literally as the air filled with ants flying en masse, landing on laundry, dropping onto heads and basking on pavements.

Entomologists say the sudden emergence of the black garden ants - known as Lasius Niger - is the insects' annual mating ritual.

Dave Clarke, head keeper at London Zoo's bugs department, describes the annual flight as "the biggest one night stand in the UK".

Black garden ants engage in annual mating ritual
Usually occurs in July or August
Timing depends on weather conditions

This airborne ant nuptial has none of the spontaneity of a bug's version of the mile-high club. The males will have been waiting for some weeks for the queens to emerge as days lengthen and weather conditions are just right.

"There has been a rise in temperature and humidity over the past few days. It has been balmy and muggy - like it is pre-thunder - which is perfect," says Stuart Hine, manager of the Insect Information Service at the Natural History Museum.

As ants from thousands of colonies take to the skies at once, the number could be millions of millions.

But why all swarm at the same time? Tom Fayle, who is completing a PHD on ants at Cambridge, says it helps maximise the chances of reproducing. But it is also a self-defence mechanism.

"A swarm keeps predators away - birds tend to eat about one in 10 of the ants."

Discarded wings

After mating, the females lose their wings and go in search of somewhere to hibernate until they lay eggs and set up a new colony.

Workers live for about a year
Queen ants can live 10-15 years
Biggest colony straddles Italian Riviera and north-west Spain and is 3,600 miles long
Source: London Zoo

"Only a few queens are successful," says Mr Fayle, "The majority won't find anywhere available and if they try to join an existing colony, they will be killed."

Once a queen has mated, she will be fertile for the rest of her life, never needing to engage in this ritual again. For the male ants, the picture is less rosy. Having fulfilled their function, they waste away and die.

While the bugs - one of about 50 species of ants in the UK - might annoy, they are harmless and pose no threat to humans, other than the odd nip.

In fact Mr Clarke says the ants pollinate flowers and feed on other insects that plague gardens. Even dead ants and discarded wings quickly disappear, eaten by swifts and swallows.

A regular feature in the BBC News Magazine - aiming to answer some of the questions behind the headlines

So when can we next expect the next swarm of flying ants?

The annual explosion tends to takes place in the UK in mid or late summer, usually towards the end of July. But although the idea of putting a fixed Flying Ant Day in the calendar has gained some notoriety, Mr Hine says the timing is not that predictable.


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