Science & Environment

Trillions of high-flying migratory insects cross over UK

butterfly Image copyright Jane Hill
Image caption Painted lady butterflies were one of the larger species recorded in the study

For the first time scientists have been able to track the hordes of high-flying insects that pass across the skies of Southern England every year.

Unseen and unnoticed by humans, researchers found that 3.5 trillion bugs and butterflies annually migrate across the region.

The researchers say their mass is equivalent to 20,000 flying reindeer.

The count was made using vertical radar and insect nets mounted on balloons.

Over a 10-year period, the scientists looked at insects flying night and day, between 150 and 1200m above the ground.

While their origins weren't recorded the researchers believe that many were travelling to and from the UK from across the English Channel and the North Sea.

Although the vast majority of the insects were tiny creatures like cereal crop aphids, flies and midges, there were also larger ones including hoverflies, ladybeetles, moths and butterflies.

Image copyright Graham Shephard
Image caption Vertical facing radar was used at several sites in Southern England to monitor the insects

One of the most surprising findings was that while the smaller insects took off regardless of wind direction, all the medium and larger creatures showed a really clear pattern of seasonal movements.

"The insects are basically measuring the wind direction and deciding whether or not to fly on that particular day or night," said Dr Jason Chapman, from the University of Exeter, the paper's co-author.

"It signifies that the insects have a compass mechanism in order to know which is north and south, but they also have the capability to then fly up high into the sky and assess the direction of the wind and relate it to the compass direction and make a decision on whether to fly or not - that's a quite complex set of things and many, many species are doing this."

The researchers found strong migrations northward in the Spring with subsequent movements south in the Autumn.

The scale of these movements essentially cancelled each other out over the period of the study.

Image copyright Ian Woiwood
Image caption Insect nets attached to helium balloons were used to trap lower flying creatures

What was also somewhat surprising were the distances covered and the speed of travel. The researchers found some insects were able to travel at 36-58 kilometres per hour, over distances of 200-300km.

The ability to study these creatures over long periods of time may be very helpful in determining the changes to the environment.

"Animal migration, especially in insects, is a very complex behaviour which takes millions of years to evolve and is very sensitive to climatic conditions," said Dr Ka S Lim, from Rothamsted Research, another author of the paper.

Image copyright Ian Woiwood
Image caption The silver Y moth is perhaps the UK's most common migrant moth

"Global climatic change could cause decline of many species, but equally other highly adaptable species thrive and become agricultural crop pests."

The researchers say that they have been able to estimate the mass of the creatures flying over the southern part of the UK at around 3,200 tonnes of biomass, which according to the authors is the equivalent of 20,000 flying reindeer.

"It's also nearly eight times the mass of the number of migratory songbirds that are coming out of the UK every year," said Dr Chapman,

"But yes, 20,000 reindeer is the correct figure, it's a calculation I did when I realised the date the paper was coming out!"

The study has been published in the journal Science.

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