Hoverflies migrate south based on a combination of the sun and their body clock, according to a new study from the University of Exeter. The experts report that the insects keep the sun on their left in the morning, then gradually adjust to navigate in the right direction.
Pied and yellow-clubbed hoverflies are important pollinators that spend their summers in places like the UK and Scandinavia, and then fly to the Mediterranean and North Africa in the fall.
While it was known that the hoverflies migrate on sunny days, the new study is the first to show that the hoverflies use a “time-compensated sun compass.”
“Simply flying towards the sun would lead them south, but this would create a winding, inefficient route,” said study lead author Richard Massy of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall.
“Our study shows that hoverflies account for the sun’s movement using their circadian rhythm. Other animals, including certain birds and butterflies, are known to have this ability. Our work suggests that it has independently evolved across multiple insects.”
For the investigation, the researchers captured migrating hoverflies at a mountain pass in the Pyrenees. The insects were placed in a type of flight simulator that confined them to one place but allowed them to freely move their bodies.
The hoverflies were positioned so that they could see the sun but not the ground, which prevented them from using landmarks for navigation. The study revealed that the flies adjust their migration route based on the position of the sun.
“Understanding how these insects navigate can help us predict their movements,” said Dr. Karl Wotton. “This could be useful for conservation measures, such as limiting the use of pesticides at key migration times.”
“Hoverflies are also important predators of crop pests such as aphids, so understanding their migrations could help us use them as natural pest controllers.”
The study is published in the journal Proceedings of the Royal Society B Biological Sciences.