Insects are the world’s smallest flying migrants, but they can maintain perfectly straight flight paths even in adverse wind conditions, according to a new study from the Max Planck Institute for Animal Behavior (MPI-AB) and the University of Konstanz. The researchers radio-tracked the migrating hawkmoths for up to 80 kilometres, the longest distance an insect has been continuously monitored in the wild. By closely tracking individuals during migration, the world’s first study reveals a century-old mystery about what insects do on their long journeys. The study, published in Science, confirms that sphinxes can accurately maintain straight paths over long distances, using sophisticated strategies to counter and correct for adverse wind conditions. The results reveal that the insects are capable of precise navigation, confirming that an internal compass guides them on their long journeys.
With billions of individuals migrating each year, insects are among the most common migratory animals on Earth. They include marquee species, such as the monarch butterfly, as well as species of enormous societal and environmental importance, such as locusts, mosquitoes and bees. But even though migratory insects far outnumber better-known migrants, such as birds or mammals, their migration is the least understood form of long-distance animal movement.
The problem, for the most part, has been methodological. “Studying insects in motion is a formidable challenge,” says first author Myles Menz, who conducted the research at MPI-AB and is now a lecturer at James Cook University in Australia. “They are usually too numerous to mark and find, and too small to carry tracking devices.”
Much of what we know about insect migration comes from studies that sample insects at a given time, such as by radar or direct observation, which has left vast gaps in our knowledge. “Understanding what insects do during migration and how they respond to weather conditions is the final frontier of migration science,” Menz says.
The current study, which tracked radiolabeled individuals in a light aircraft, is the first to continuously study nocturnal migrating insects in the wild and represents the longest distance an insect has been continuously tracked in the field. The team, which includes researchers from MPI-AB and the University of Konstanz in Germany and the University of Exeter in the UK, focused on the death’s-head hawk-moth, a large nocturnal migrant which travels up to 4,000 kilometers between Europe and Africa each year. year. Like many insects, the species is a multigenerational migrant, meaning that no individual knows the entire journey.
At MPI-AB in Konstanz, Germany, the team bred caterpillars to adulthood in the lab to make sure the individuals were naïve. When the moths emerged as adults, they were affixed with radio beacons weighing 0.2 grams, or less than 15% of adult body weight. “Butterflies would probably eat more weight than that in one night, so these tags are extremely light on insects,” Menz says.
The researchers released the tagged butterflies and waited for flight to begin, after which they chose a single individual to track at a time. The team tracked 14 moths each for up to 80 kilometers or 4 hours – a stretch long enough to be considered a migratory flight – using antennae mounted on a Cessna aircraft to detect precise locations every five to 15 minutes. The insects were tracked in a south-southwest direction from Konstanz in the Alps, which follows the route taken by the sphinxes to the Mediterranean and northwest Africa.
Due to the practical constraints of flying in airplanes, the scientists tracked the moths continuously until the insects stopped en route. “When you’re on a plane, it becomes extremely difficult to wait for the insects to start migrating again because you would have to be in the air when it happens, which could be any time of the night,” says the lead author. Martin Wikelski, a movement ecologist from MPI-AB and the University of Konstanz, who piloted the plane during the study.
The results show that the butterflies maintained perfectly straight trajectories over long distances during flight. It wasn’t because they were expecting favorable winds. Instead, they used a range of flight strategies to shield themselves from prevailing winds, allowing them to maintain their course throughout the night. When the winds were favorable, they flew high and slow, allowing the air to carry them. But in strong headwinds or crosswinds, they would fly low to the ground and increase their speed to maintain control of their path.
Says Menz: “For years it was assumed that insect migration was mostly about getting swept away. But we show that insects are capable of being great navigators, on par with birds, and are much less vulnerable to wind conditions than we thought.
“By showing that it is technically possible to continuously monitor individual insects as they migrate and observe their flight behavior in detail, we hope to inspire further studies to answer many other big questions in this field. .”
For the study authors, the next step is to answer the question of how butterflies are able to maintain such straight lines. “Based on previous lab work, it’s possible that insects use internal compasses, both visual and magnetic, to navigate their way around the world,” Menz says.