Thousands of fireflies glow in unison in Oita Prefecture in Japan.

Scientists believe they synchronise to avoid confusing the females

Men would not get away with it - but mass flashing is a necessary way for some male fireflies to attract a partner.

Scientists have discovered why the bugs sometimes flash in unison, with large groups producing synchronised, rhythmic pulses of light that can illuminate a whole forest.

They do it to ensure females do not get confused and can recognise members of their own species, research published in the journal Science has shown.

Flashing is the mating tool of fireflies, which are really a type of beetle.

The patterns consist of one or more flashes, followed by a characteristic pause. During the pause, females perched on leaves or branches will produce a single response flash if they spot a suitable male.

But a problem arises when large numbers of males gather in the same place, creating a cluttered landscape of flashes. Then the characteristic flashes of one's own species might be difficult for a female to recognise.

The solution is for all the males of the same species to flash in synchrony, producing a pattern that cannot be missed.

US scientists demonstrated the effect in the laboratory by exposing females of the firefly species Photinus carolinus to light emitting diodes (LEDs).

Each of the lights produced the species-specific pattern for P. carolinus, mimicking male fireflies.

When the LEDs flashed in sync, the females responded 80% of the time. But when the flashes were out of sync they only produced a 10% response rate, the scientists found.

'There have been lots of really good observations and hypotheses about firefly synchrony, but until now, no one has experimentally tested whether synchrony has a function,' said study leader Dr Andrew Moiseff, from the University of Connecticut.

'When males are flashing in high densities, the female's inability to focus on just one male would make it very difficult for her to detect her species-specific pattern. So if the males synchronise, it can maintain the fidelity of the signal in the presence of many other males.

'Animals have evolved to solve unique problems in many different ways, and I'm interested in how they do that. Fireflies have these tiny heads and these tiny brains, but they can do some complex and amazing things.'