Migration is a marathon – not a sprint – for hoverflies

Migratory hoverflies fly further – but not faster – than their non-migratory relatives, new research shows.

Scientists caught migrating marmalade hoverflies in the Pyrenees, and non-migrating members of the same species in the UK.

Each hoverfly was tested on a special “tether” before being released unharmed.

The hoverflies could continue to fly while tethered, and the migrating ones flew twice as far.

Meanwhile, hoverflies with fat abdomens – showing they were well fed – flew five times as far as thin ones, suggesting this stored energy is vital.

Abdomen size and migration habits did not affect flight speed, although larger hoverflies flew faster than smaller ones.

“Migratory creatures such as birds generally move faster when they’re migrating,” said Richard Massy, from the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall.

“So we were surprised to find this is not the case for marmalade hoverflies.

“For these insects, migration is a marathon – not a sprint.

“Flying faster is usually more energy-efficient – but these hoverflies might throttle their speed to a sustainable pace to minimise muscle wear and maintain their condition over long distances.”

Marmalade hoverflies, which are found across much of Europe, behave differently depending on location and the time of year.

Hoverflies that reach adulthood in summer live short lives of weeks to a month before breeding and dying, giving rise to multiple generations each year.

In autumn, however, hoverflies delay their reproduction – which lengthens their lifespan until the following spring. For those in northern areas such as the UK, autumn also triggers a southward migration.

The importance of body condition – as measured by abdomen size – highlights the need for food sources (flowers) along this journey.

Dr Karl Wotton explained: "If these resources are depleted through habitat loss and fragmentation, or if they are out of synchrony with migratory movements, then the consequences for the success of migration may be severe.

“This could help explain some of the declines recently seen in the numbers of migratory hoverflies."

Explaining more about the species, Dr Will Hawkes said: “Marmalade hoverflies are an abundant and colourful hoverfly, often seen in our gardens across the UK.

“They are very beneficial pollinators and naturally control pests such as aphids, helping reduce crop damage.

“Despite being only 1cm in length, they undertake huge migrations across Europe: southwards in autumn, northwards in spring.

“We don’t know how far individuals migrate but we suspect that migrations in excess of 1000km are common.”

The migrating hoverflies in the study were caught at the Puerto de Bucharuelo mountain pass on the border of France and Spain, while the summer hoverflies were caught at the Penryn Campus.

The study was funded by the Natural Environment Research Council and the Royal Society.

The paper, published in the journal iScience, is entitled: “Enhanced flight performance in hoverfly migrants.”

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