Every autumn, more than 17 million insects pass through a single 30-metre-wide mountain gap on the border between France and Spain, new research shows.
A team of scientists have made the remarkable discovery that every autumn over 17 million insects migrate through a narrow mountain pass high up in the Pyrenees on the border between France and Spain.
The team visited the pass each autumn for four years monitoring the vast number and variety of insects heading south.
Based on the findings from this one pass, which represents the easiest route through the high mountains for the insects, the researchers now believe that billions of insects migrate through the Pyrenees every autumn making it a key location for many migrating insect species.
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The research has its origins back in 1950 when British ornithologists Elizabeth and David Lack made the chance discovery that large numbers of marmalade hoverflies were migrating through the mountains, the first recorded instance of fly migration in Europe.
In 2018 the researchers visited the same pass to see if the migration was still happening and were astonished by what they found then and in the subsequent four years.
“Not only were vast numbers of marmalade hoverflies still migrating through the pass, but far more besides,” says Will Hawkes from Exeter University.
“These insects would have begun their journeys further north in Europe and continued south into Spain and perhaps beyond for the winter. There were some days when the number of flies was well over 3,000 individuals per metre, per minute.”
Hawkes adds that one of the most magical things that the team found migrating through the Pyrenean pass were cabbage white butterflies.
“I always believed that these butterflies would stay in our gardens all year round, hibernating in the winter, but we found them migrating in their thousands.”
Whilst bird migration is well studied, Hawkes says that we are just beginning to understand insect migration in Europe and around the world.
“Insect migration is a really understudied field that is just beginning to blossom,” states Hawks.
“However, there are already some fascinating tidbits of stories of insect migration. For example, we know that insects migrate across the European Alps and we think that some dragonflies migrate across the Indian Ocean.”
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