Hoverflies use sun and body clock to navigate when they fly south for winter, study finds

Hoverflies use a combination of the sun and their body clock to help direct them when flying south for the winter, new research shows.

Findings show the insects keep the sun on their left in the morning then gradually adjust to maintain a southward route as the day goes on, in what scientists at the University of Exeter believe is the first proof of a “time-compensated sun compass” in hoverflies.

In summer, pied and yellow-clubbed hoverflies – which are important pollinators – are found in locations such as the UK and Scandinavia before they fly off to the Mediterranean and North Africa in autumn.

While it has been known for some time that these migrations take place on sunny days, the study confirms the insects “account for the sun's movement using their circadian rhythm,” according to lead author Richard Massy.

“Other animals, including certain birds and butterflies, are known to have this ability. Our work suggests that it has independently evolved across multiple insects,” Mr Massy, who works at the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall, said.

“Simply flying towards the sun would lead them south, but this would create a winding, inefficient route,” he added.

The hoverflies were caught at a mountain pass in the Pyrenees and placed into a flight simulator, which held them in place but allowed them to swivel freely.

They could see the sun, but not the ground, meaning they could not navigate using landmarks.

Researchers – who published their results in the Proceedings of the Royal Society B journal – found that the creatures headed south by adjusting their course based on the sun’s position and the time of day.

To further test the theory, scientists places some of the hoverflies in an artificial lighting environment for several days to shift their body clocks, then tested their navigation.

With their circadian rhythm disrupted, the direction of flight shifted westward – supporting the conclusion that they navigate using a time-compensated sun compass.

Dr Karl Wotton, of the University of Exeter, said: “Understanding how these insects navigate can help us predict their movements. 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,” he added.

The research team included experts from the University of Bristol, with funding allocated from the Royal Society and the Natural Environment Research Council’s GW4 Doctoral Training Programme.