How Migrating Death’s-Head Hawkmoths Fly Along a Straight Path
No prior study had continuously monitored wild, nocturnal migrating insects
The Death’s-head hawkmoth (Acherontia atropos) is known by many for its role in The Silence of the Lambs—but perhaps the insect’s bigger feat is its staggeringly precise migration.
Every year, these moths with skull-like markings fly well over 2,000 miles from Europe to Africa. As they fly, they move along a remarkably straight path, regardless of wind conditions. Scientists know little about how these moths—or any migrating insect—can cover such long distances so efficiently.
“Studying insects on the move is a formidable challenge,” Myles Menz, an ecologist at James Cook University says in a statement. “They’re usually too numerous to mark and find again and too small to carry tracking devices.”
But advances in technology have considerably shrunk the size of animal-tracking radio tags, and death’s-head hawkmoths—with their wingspan of about 5 inches—are larger than most insects. This lets them fly unhindered with a tag attached to their back.
In a study published in Science in August, Menz and his colleagues at the Max Planck Institute of Animal Behavior attached tracking devices weighing about 0.2 grams to 14 moths and followed their migration in an airplane. Before this, no other study had continuously monitored wild, nocturnal migrating insects, per the statement.
“They have been trying to do this with insects, and they finally got it,” Gerard Talavera, an ecologist at the Botanical Institute of Barcelona who was not involved in the study, tells National Geographic’s Jason Bittel. “It is fantastic to see people doing brave work like this.”
The team tracked one particular moth for just under 56 miles, which marks the longest distance an insect has been continuously tracked, write Menz and co-author Martin Wikelski in The Conversation.
Wikelski, a migration researcher with the Max Planck Institute of Animal Behavior, flew the moth-tracking airplane. Receiving antennas on the aircraft detected the animals’ precise location every five to 15 minutes as he followed them for up to four hours each, per The Conversation. They got detailed data from seven of the moths.
The researchers found that death’s-head hawkmoths actively changed their flight strategy based on how the wind was blowing.
"If there were favorable tailwinds following [the moths], they flew up a bit higher and took advantage of these winds, which were going south-west,” Menz tells Nick Kilvert of the Australian Broadcasting Corporation (ABC). “The other strategy was to fly partly downwind and offset a bit and make an adjustment [along the journey].”
If the winds were unfavorable, moths would fly down low and “basically punch into it,” Menz tells the publication. Flying closer to the ground gives the moths more speed and control, because that way, they’re “getting some buffering from the wind,” he tells the ABC.
Still, exactly what system these insects use to stay their path remains a mystery, and it’s a question the team hopes to address in future research.
“Are they following the Earth’s magnetic field? Or perhaps relying heavily on visual cues?” write the authors in The Conversation. “The more we understand, the closer we can get to being able to predict the phenomena of insect migration. And this would have broad implications—from managing threatened species and species with agricultural benefits, to having better control over agricultural pests.”