Diamondback moths: an epic journey
Miniscule moths are using the power of wind to soar over oceans and continents.
Gardeners up and down the UK noticed the arrival of thousands of tiny brown insects to our shores in the first week of June.
Droves of diamondback moths (Plutella xylostella) filled the country's fields and hedgerows.
Suddenly everywhere, these creatures are likely to have made a mammoth journey to be here.
Microlepidoptera curator Dr David Lees says that although it isn't clear when exactly the first females arrived, the wind is likely to be responsible for their speedy voyage.
Diamondback moths can migrate huge distances. They are found all over the world, from Scandinavia to Australia and the Americas.
One of the most widely distributed moths or butterflies on the planet, they feed on cruciferous vegetables like broccoli and cabbage. Human migration has also helped the spread of the species.
Like many moths, the diamondback cannot survive low temperatures, and does not spend the winter in the UK. Scientists think that the moths arrive in cooler countries - including the UK - by riding on strong wind currents.
A gardener's enemy
Diamondback moths are considered a pest, and are one of the most destructive species in the world when it comes to cruciferous vegetables.
Since the 1980s, the species has developed immunity to some common pesticides, and can lay waste to crops.
Despite a short life cycle of about a month, or a few weeks in hot conditions, they are able to produce many offspring during their adult lives. This can number up to 300 per female.
Population levels vary from year to year and from location to location, depending on environmental conditions, predators, and migrations.
A windy journey
When they are seen in Britain, they have usually travelled huge distances. Despite these long journeys, the diamondback has a wingspan of just 15 millimetres and is a weak flyer.
It relies on the elements to carry it across the planet.
David says, 'We are seeing millions of diamondback moths in Britain at the moment, especially around the south coast.
'These moths can arrive via very high wind currents, including winds from the Sahara desert.
'But this explosion started at the beginning of June, and at that time the winds were blowing from the north. So it might be a huge emergence of the first generation that arrived long-haul earlier this year - possibly in March or April.'
Why the long trip?
It is known that the tiny moths can travel on the wind uninterrupted for several days. They can cover distances of more than 2,000 miles, at a speed of more than 300 miles per night.
An outbreak of the species in 1958 saw a deluge in northeast England and eastern Scotland that caused chaos.
Reports from the time say that the moths entered houses in such numbers as to cause alarm, cyclists were forced to ride through swarms, and car drivers had to stop and clean their windscreens.
Time will tell if this summer's outbreak will become so large, but millions of diamondbacks are estimated to have hit the south coast from around 1 June.
David says, 'Often with organisms that behave this way, there is some trigger that puts them into their migratory phase. In this phase, population increases can be quite substantial, and the moths are unusually active by day as well as by night.
'They are weak flyers but it seems they just spread their wings and are taken up like plankton by the wind and dispersed long distances.
'The precise mechanism that allows moths to know when and where to migrate is not fully understood.'
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