Thousands of people participating in this year's National Moth Night over the coming nights of 18-19 September are being asked to look out for moths that have been specially marked at sites across Britain and Ireland.
It's part of a nationwide experiment to study the flight routes of moths.
The marked moths - mostly migrants from Europe - have been caught, mainly at locations along the south and east coast, given a small dot of colouring and then released unharmed earlier this week.
Mark Tunmore, National Moth Night co-ordinator said: "National Moth Night sees enthusiasts up and down the country gather around moth traps to inspect the huge variety of moths found in the UK. It is hoped that they will find some of the marked moths in their traps, providing information about how far and in what direction they fly once they arrive in this country.
"Bird ringing has revolutionised our understanding about where our birds fly to, both within Britain and other parts of the world, but in the case of our moth populations we simply have no idea how much movement takes place within our resident populations, or indeed where many of the millions of migrant moths that arrive on our shores end up.
"September is a particularly exciting month for moth migration in Britain and we are hoping for favourable winds to bring across some unusual visitors."
Altogether there are 2,500 different types of moth seen in this country. Contrary to popular belief, many are brightly coloured, some fly during the day as well as at night and only six of these species ever damage stored clothing.
Richard Fox, who heads Butterfly Conservation's involvement in National Moth Night, said: "The worrying fact is that moth numbers are in serious decline, especially in the southern half of Britain.
"Moth caterpillars play a vital part in the food chain for many birds and bats. Without moths, the whole of biodiversity starts to unravel. National Moth Night will help us better understand moths and develop conservation strategies."
The colouring used to mark the moths has been shown to be harmless, with moths being seen five months after they were first coloured.
Richard said: "We realise that probably only a few of the marked moths may be found in traps. There are many millions of moths flying on any one night so encountering one of the marked moths is unlikely, but just about possible."