Of all the insects that migrate through the Bujaruelo pass in the Pyrenees, flies make up 90%, with ... [+]
Perched between two majestic peaks in the Pyrenees on a blazing hot September afternoon, scientist Will Hawkes glanced down at his feet to witness a stunning sight. “There were so many small orange/yellow flies it was as if the ground had become a living carpet humming with energy,” he recalled.
If insects had their own Yelp, the mountain pass along the border of France and Spain would top the rankings for popular thoroughfares. More than 17 million insects migrate through it annually, according to a new study that spotlights the astounding number and variety of the winged travelers. Hawkes, an insect migration researcher, is the study’s lead author.
In 1950, ornithologists Elizabeth and David Lack chanced upon a massive number of striking, orange-bodied marmalade hoverflies zipping through the high-altitude crossing at once. Nearly 70 years later, Hawkes and fellow researchers returned to the Bujaruelo pass in the Spanish province of Huesca to see whether a decline in some insect species due to factors such as habitat loss and climate change had impacted the migration.
“What we found was truly remarkable,” said Hawkes, who works at the Centre for Ecology and Conservation at the University of Exeter in Cornwall, England. “Not only were vast numbers of marmalade hoverflies still migrating through the pass, but far more besides.” A whopping 20 families of diurnal insects from five orders, in fact—flies, wasps, butterflies, dragonflies—many benefitting ecosystems as they travel.
Scientists Karl Wotton and Scarlett Weston set up a moth trap in the Bujaruelo pass, which has ... [+]
Insects migrate north in spring before returning south in autumn in the northern hemisphere. The insects described in the study, which appeared Wednesday in the journal Proceedings of the Royal Society B, would have begun their journeys further north in Europe and continued south into Spain, with some advancing as far as Africa for the winter.
A majority of the migrating insects are pollinators that transfer pollen, and the genetic material contained within, between geographically isolated plant populations, increasing the plants’ genetic diversity. Some of the little globetrotters count as crop-damaging pests, but others act as pest controllers. All of their bodies contain nutrients such as nitrogen and phosphorus, which aid plant growth. When the insects die, the soil absorbs them as healthy organic waste.
The scientists estimate that billions of arthropods thrum their way through variousPyrenees routes annually. They can’t fly over 9,800-foot peaks, so they get channeled by the steep-sided mountain valleys and up over the mountain passes. The Bujaruelo pass, which measures 98 feet wide, proved a perfect spot for the scientists to station themselves with their equipment and observe the mechanics of one mass migration.
“The combination of high-altitude mountains and wind patterns render what is normally an invisible high-altitude migration into this incredibly rare spectacle observable at ground level,” team leader Karl Wotton, a bioscientist at the University of Exeter, said in a statement.
Starting in 2018, Wotton, Hawkes and their fellow researchers visited the site every fall for four years to monitor the number of day-flying insects migrating south through the pass and identify the species. You can watch one of their videos of migrating hoverflies below.
The team used video footage shot at 15-minute intervals to count migrating insects less than a tenth of an inch long and relied on their eyes to quantify larger butterflies and dragonflies. They caught insects in a flight intercept trap so they could later identify them under a microscope.
Insect totals peaked in warm, sunny and dry conditions, when low wind speeds and headwinds kept the critters low over the pass and accessible for counting.
“To see so many insects all moving purposefully in the same direction at the same time is truly one of the great wonders of nature,” Wotton said.
The researchers identified a range of insects, but flies made up 90%, with the marmalade hoverfly being the most common. On some days, the team observed more than 3,000 flies per meter per minute. “I had no idea these tiny insects would leave my garden, let alone fly thousands of kilometers across continents,” Hawkes said.
The scientists hope their new study will highlight the wonders of insect migration, while also calling attention to the importance of protecting migrating insects that may be facing threats from land use changes, a shifting climate and pesticides.
“By spreading the knowledge of these remarkable migrants,” Hawkes said, “we can spread interest and determination to protect their habitats.”
Every year, some 17 million insects zip through this mountain pass along the border or Spain and ... [+]
