A new study has radio-tracked migrating Death’s-Headed Hawkmoths for up to 80 km—the longest distance any insect has been continuously tracked in the wild.
By closely following individuals during their migration, a world-first study unlocks the century-old mystery of what insects do during their long-distance journeys.
The findings reveal that the beetles are capable of precise navigation, confirming that an internal compass guides them on their long journeys.
The study was published in the journal Scienceconfirms that hawkmoths can precisely maintain straight trajectories over long distances using complex strategies to counter and correct adverse wind conditions.
Tagged Death’s-headed Hawk Moths have been observed flying up to 80 km in a straight line (John Evans).
With trillions of people migrating each year, insects are the most common migratory animals on Earth. But while insect migrants are far more numerous than better-known migrants such as birds and mammals, their migrations are the least understood form of long-distance animal movement. The problem was mainly methodological.
“Studying insects in motion is a very challenging task,” said first author Myles Menz, who conducted research at the Max Planck Institute for Animal Behavior (MPI-AB) and is now a lecturer at James Cook University in Australia. “They are usually too numerous to tag and find again and too small to carry tracking devices.”
Much of what we know about insect migration comes from studies that sample insects at one point, such as by radar or direct observation, which leaves large gaps in our knowledge.
“Understanding what insects do during migration and how they respond to weather conditions is the final frontier in migration science,” Menz said.
The current study, which followed radio-tagged individuals in a light aircraft, is the first study to continuously study nocturnally migrating insects in the wild and represents the longest distance any insect has been continuously tracked in the field.
The Death’s-headed Hawkmoth is a large, nocturnal migrant that travels 4,000 km between Europe and Africa each year. Like many insects, the species is a multigenerational migrant, meaning no individual knows the entire route.
At MPI-AB, the team raised the caterpillars to adulthood in the laboratory to ensure that the individuals were naïve. When the butterflies emerged as adults, they were fixed with radio tags weighing 0.2 grams—less than 15% of the adult’s body weight.
“Moths will probably eat more than that weight in one night, so these tags are very light on insects,” Menz said.
The researchers released the tagged moths and waited for the flight to begin, after which each time they chose an individual to follow.
They tracked 14 moths for up to 80 km, or up to 4 hours each, using Cessna-mounted antennas to detect precise locations every 5 to 15 minutes – long enough to be considered a migratory flight. The beetles were followed south-southwest from Constance to the Alps, following the route taken by hawkmoths to the Mediterranean and northwest Africa.
The Death’s-head Hawkmoth migrates between Africa and Europe every year (Doug Kelson).
Due to the practical limitations of flying in an airplane, the scientists tracked the moths continuously until the insects stopped en route.
“When you’re on a plane, it’s very difficult to wait for insects to start migrating again because you have to be in the air when that happens, which could be any time tonight,” said lead author Martin Wikelski. A traffic ecologist from MPI-AB and the University of Konstanz who piloted the aircraft during the study.
The results show that moths maintain perfectly straight trajectories for long distances in flight. It wasn’t because they were waiting for favorable tailwinds. Instead, they used a number of flight strategies to buffer against the prevailing winds, allowing them to continue their course through the night. When the winds were favorable, they flew high and slow, letting the air carry them. But in strong winds or crosswinds, they fly towards the ground and increase speed to control their path.
“For years it was assumed that insect migration was mainly about flying around. But we show that insects can be great navigators, just like birds, and are less sensitive to wind conditions than we thought,” Menz said.
“By showing that it is technically possible to continuously track individual insects during migration and observe their flight behavior in detail, we hope to inspire more research to answer even more big questions in this field.”
Co-author Dr Jason Chapman, an expert on insect migration at the University of Exeter, commented: “We’ve known for a number of years that migratory insects prefer migratory routes that change seasonally, but what was really surprising about this new study was how hawkmoth tracks travel very long distances. was flat – they really stretched for tens of kilometers to the winter growing areas.
“This means that they are constantly adjusting their flight directions in real time to correct for cross-wind drift, just like bees returning to their hives, only at much greater distances – and this was a complete surprise.”
The next step for the study authors is to answer the question of how the moths are able to maintain such straight lines. “Based on past lab work, it’s possible that insects use both visual and magnetic internal compasses to navigate their way around the world,” Menz said.
Menz, MHM, Scacco, M, and 5 others. Individual tracking reveals long-range flight path control in a nocturnally migrating moth. Science, vol. 377, pp. 764-768. DOI: 10.1126/science.abn1663