Bats feast on migrating insects in the Pyrenees

Each fall, high up in the Pyrenees mountains, an extraordinary natural phenomenon unfolds. As nocturnal insects migrate south, bats gather in large numbers to feast upon them, according to research from the University of Exeter

The experts report that these bats – both migratory and local – take advantage of the behavior patterns of insects, utilizing them as a vital food source.

Hotspots for migratory insects

The study was conducted at the Pass of Bujaruelo, located close to Spain’s border with France. The research has presented some groundbreaking revelations. 

Scientists identified seven distinct bat species and an impressive 66 insect species in this region. What’s even more fascinating is that 90 percent of these insects are moths.

Dr. Will Hawkes from the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall noted, “Mountain passes are hotspots for a wide variety of insect species that fly south in the autumn.” 

Activity spikes for a few days

Dr. Hawkes also pointed out that this grand spectacle lasts for only about two months each autumn. Weather conditions, being as unpredictable as they are, only allow three or four primary nights where vast numbers of insects fly through the Pass of Bujaruelo. 

On these pivotal nights, the activity levels of both migratory and residential bat species see a significant spike.

This research presents the first evidence of migratory bats consuming migratory insects during their concurrent migrations. 

Refuelling station 

Dr. Hawkes suggests that these bats may consider the influx of insects as a “refuelling station” for their own lengthy voyages southward. This interconnectedness between bats and insects draws attention to the fragility of ecosystems.

Dwindling moth numbers in the UK and the myriad threats they face – from climate change and light pollution to pesticides and habitat loss – underscore the potential repercussions on bat populations. 

Study implications 

Considering that some of these insects travel hundreds or even thousands of miles, they face multiple challenges that could, in turn, affect the bat species.

One noteworthy example is the European free-tailed bats, inhabitants of these mountains. Born in the autumn, their young are particularly reliant on the insect migrations for sustenance and to accumulate energy essential for hibernation.

Among the bat’s prey is the cotton bollworm moth. Known for its caterpillars that often plague crops, by consuming such species, bats inadvertently extend a pest-control service beneficial to humans.

A lucky encounter 

Recounting the origins of this study, Dr. Hawkes recalls a fateful night in 2018. While in the pass with co-author Karl Wotton, the researchers overheard the feeding buzzes of bats, leading to the theory that bats might be specifically targeting migratory moths during their own migrations.

“It was this lucky encounter of us being in the right place at the right time that made us think that maybe the bats are specifically targeting the migratory moths as the bats themselves migrate too,” said Dr. Hawkes. 

“The sheer level of activity at the pass of both bats and insects was amazing to see,” noted co-first author Kelsey Davies.

The study is published in the journal Royal Society Open Science. 

More about migratory insects 

Migratory insects are fascinating creatures that undertake substantial journeys, often traveling hundreds or even thousands of miles during their lifetimes. 

These migrations are typically driven by seasonal changes, environmental conditions, and the search for food or breeding grounds. 

Monarch butterflies 

Perhaps the most famous migratory insect, the monarch butterfly, travels thousands of miles from North America to Central Mexico and back. This migration occurs over several generations, with each generation completing a portion of the journey.

Dragonflies

Some species of dragonflies, like the globe skimmer or wandering glider, are known to migrate across the Indian Ocean between India and Africa. They travel thousands of miles, which is impressive given their delicate appearance.

Locusts

Swarms of locusts are infamous for their migrations, which can devastate large areas of vegetation. Driven by environmental factors, locust swarms can travel great distances in search of food.

Moths

Many moth species, like the Silver Y moth, undertake long migrations, often traveling from Southern Europe to Northern Europe and back.

Whiteflies

These tiny insects can migrate longer distances, often aided by wind currents, moving from crop to crop and causing considerable damage.

Reasons for migration

Seasonal changes

Many insects migrate to exploit seasonal variations in resources. For example, they may move to cooler areas during hot periods or to warmer areas during cold periods.

Reproduction

Some insects migrate to find suitable breeding grounds or to avoid competition.

Food availability

If food sources become scarce, insects might migrate to areas with a more abundant supply.

Navigation

One of the great mysteries surrounding insect migration is how they navigate during these vast journeys. Studies suggest they use a combination of the Earth’s magnetic field, polarized light, and visual landmarks.

Challenges

Migratory insects face numerous challenges, including adverse weather conditions, predators, and the sheer physical demands of long-distance travel. 

In addition, human-made challenges such as light pollution and habitat destruction can interfere with their migrations.

Image Credit: Will Hawkes

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