Buzzing insects may be seen as pests – but globally, hundreds of fly species migrate over long distances, with major benefits for people and nature, new research shows.
Insects such as houseflies, fruit flies, blowflies, hoverflies and mosquitoes all belong to an order called Diptera, which contains over 125,000 known species, and possibly over a million in total.
Myles Menz, co-author of the new study and Senior Lecturer in Zoology and Ecology at James Cook University, said researchers found almost 600 of these species are likely to be migratory, and the true number is probably far higher.
This is important because these insects play multiple important roles, including as pollinators, pest controllers and decomposers.
With insect numbers declining worldwide, the review highlights the need for complex, connected habitats to support flies along their epic journeys.
Lead author Dr Will Hawkes, from the Centre of Ecology and Conservation on the University of Exeter's Penryn Campus in Cornwall said migrating flies play an unparalleled range of ecological roles, making them a major force in ecosystems and the economy.
"Many of the species that benefit humans are under threat from climate change and other human impacts and many could disappear without ever being documented unless action is taken.
"To conserve them, it will not be enough to protect or restore habitat at single locations; the entire migratory route must be capable of sustaining these insects," said Dr Hawkes.
Co-author, the University of Exeter's Dr Karl Wotton, said the priority should be improving "connectivity" – linking insect-friendly areas across landscapes.
"Worldwide, factors including urbanisation, intensive agriculture and destruction of wetlands have made large areas unfriendly to insects, potentially creating damaging gaps on insect migration routes," Dr Wotton said.
The researchers said that pollinating hoverflies alone have been found to visit 52% of major food crop plants globally (these crops have an estimated worth of around US$300 billion per year).
Highly mobile species may also connect distant habitats, moving genetic material, such as pollen, back and forth, boosting the genetic diversity of plants.
As well as the loss of direct benefits, the decline of such insects also affects wider biodiversity.
For example, the number of insect-eating birds in North America has dropped by an estimated 2.9 billion in the past 50 years, while numbers of non-insectivorous birds have increased by 26.2 million.
"What we've uncovered is that Dipteran migrants are vital to the planet's ecosystems, yet they are hugely underappreciated. This review will hopefully inspire many more studies into this fascinating and important world of fly migration," said Dr Menz.
The study was funded by the Royal Society.
The paper, published in the journal Biological Reviews, is entitled: "Lords of the flies: dipteran migrants are diverse, abundant and ecologically important."
Notes:
The researchers highlighted examples of notable migrating flies:
- The larvae of just two hoverfly species (marmalade and vagrant hoverflies) eat an estimated 10 trillion aphids each year in southern England alone, showing their vast power as pest controllers.
- Autumn houseflies (Musca autumnalis) play a vital role as decomposers. A study on the closely related housefly (Musca domestica), showed that the larvae produced by just 50 flies (25,000 eggs) can decompose up to 444kg of pig slurry, transforming it into organic compost. Autumn houseflies have been found migrating through high passes in the Pyrenees.
- Other fly species embark on a more sinister journey: reindeer botfly may track reindeer on their own lengthy migrations – and the female flies expel their larvae into the noses of reindeer to live in their throats until spring.
- Some migrating flies are moving into new areas due to global warming; mosquitoes have recently carried malaria into mountainous regions of Nepal.
