It’s a strange migration that takes place every autumn, at the Bujaruelo pass (Hautes-Pyrénées), near the Gavarnie cirque, between France and Spain. A British scientist and his team published a study on June 12 in the journal Royal Society on this mass migration of more than 17 million insects crossing this Pyrenean pass, only 30 meters wide. Every fall, from 2018 to 2021, Will Hawkes’ team of researchers went to Bujaruelo Pass to install cameras and traps to observe this extraordinary phenomenon, known since the 1950s.
“We identified 20 families of diurnal insects belonging to five orders exhibiting migratory behavior judged by directional movement across the Bujaruelo pass,” the team of scientists indicates in its research articles. Diptera (flies, mosquitoes, midges, etc.) dominated the migratory assemblage and the annual number varied more than four times. The numbers at this single site hint at the likely billions of insects crossing the entire Pyrenees mountain range each year.”
3,683 individuals per meter per minute
At the height of this massive migration wave, compared to “a blizzard of yellow and white butterflies, like a storm of petals”, the researchers counted 3,683 individuals per meter per minute. Of this swarm of insects, butterflies represent only 0.4% of the total of these migrants, the most numerous being the Syrphidae, a family of flies, with an average of 3.1 million per season.
According to this study, temperature, wind direction and rainfall influenced the importance of this movement of insects from Western Europe towards the south, into Spain and for certain species as far as Africa.
