Source: ForeignAffairs4
Source: The Conversation – UK – By Toby Doyle, Research Associate, Centre for Ecology and Conservation, University of Exeter
On a North Sea oil rig several years ago, an engineer noticed a strange phenomenon. A cloud of insects would descend from the sky and land on the upper reaches of the platform.
There were thousands of them, carpeting the superstructure and barely moving. They would sit there for a few hours, then suddenly they would all rise up into the sky and fly off again.
The engineer, whose name was Craig Hannah, was also a keen naturalist and photographer. He saw the same thing happening repeatedly and wondered if it would be of interest to insect researchers. This led him to the University of Exeter’s Centre for Ecology and Conservation, to which we are both affiliated.
Craig diligently collected small specimen-tubes of flies at the rig, which is in the UK Britannia oil field, and they started arriving regularly on our desks. We’ve spent the past few years studying them, and the results have now been published for the first time.
The insect cloud mostly consisted of hoverflies. Hoverflies are a stripey little class of winged insects that sometimes get mistaken for wasps or hornets. They play an unsung role as nature’s pest controllers, gobbling up aphids on plants, and also have another important claim to fame: they are the second most important pollinators after bees.
Unlike bees, which are territorial creatures that generally stay in their patch, hoverflies can move over great distances. If you’re wondering why they don’t become the king pollinators as a result, it’s to do with their larvae.
Bee larvae depend on nectar and pollen, so when bees land on flowers, they are collecting for the hive. Infant hoverflies, on the other hand, eat aphids, leaving adult hoverflies to gorge on all the pollen and nectar themselves.
Long insect journeys
It has been shown before that insects can carry pollen for many miles. Painted Lady butterflies, for instance, have been shown to travel from west Africa all the way to French Guiana in South America.
The evidence about hoverflies has been more limited. There was a 2019 paper from our centre that used radar to show billions of them carrying pollen across the English Channel. But for the first time, our paper shows this happening over much greater lengths.
We focused on the marmalade hoverfly, so-called because of its distinctive orange and black stripes, which made up a large proportion of the flies landing on the rig. There were also a lot of other hoverflies, particularly the common hoverfly, as well as some blowflies and root-maggot flies. (It’s not unusual for different insect species to move together in this way; we’ve previously observed it in mountain passes in the Pyrenees, for instance).
From analysing the pollen on the bodies of the marmalade hoverflies, we showed that they were carrying it from as far as 500km away. This was only part of a much bigger journey, however.
Just like birds, some species of hoverfly migrate with the seasons. They move to southern Spain in the early autumn and then as far north as Norway in spring (the northern leg is less well understood, and seems to take place over several generations, since each fly only actually lives for a few weeks).
This migration is an incredible feat of nature: hoverflies don’t go all the way to sub-Saharan Africa in the way that, say, swallows would, but they move much more slowly so there’s perhaps an even greater effort involved overall.
We know from previous research that many insects will make these trips by burning carbohydrates and stores of body fat. Thankfully their pollen luggage is at least light, so it’s not making the journey much more arduous. That said, the flies seem exhausted when they land on the oil platforms. Craig was able to coax them into specimen tubes with a little nudge.
The pollen count
The flies’ pollen came from a much wider range of plants than might have been expected – more than 100 species in all – which demonstrates why these insects are such good pollinators. The most common types on their bodies were common nettle, black elder and meadowsweet, all of which are ubiquitous from one end of Europe to the other.
One thing that isn’t yet clear is whether by the time it has been carried long distances, this pollen is viable for pollination (it may have been degraded by UV light for instance). There weren’t ideal conditions for preserving the insects on the oil rig, meaning that the pollen was always dead by the time it reached us.
We’re aiming to remedy that in future either by finding a better way to store the flies or by collecting them ourselves on another site. We also have a PhD student looking at the physiology of hoverflies, to get a better understanding of how they are able to migrate such long distances.
Meanwhile, Craig is still sending us regular samples, and now even has a friend providing a similar service from a neighbouring rig. This is enabling us to study all the species of hoverflies that land on the rig to see if they have the same pollen preferences as their marmalade cousins. It’s a great example of how fruitful a collaboration can be between researchers and members of the public. If anyone else is encountering bugs behaving unusually, we’d love to hear from you.
Toby Doyle is affiliated with The University of Exeter.
Eva Jimenez-Guri is affiliated with The University of Exeter.
– ref. Thousands of flies keep landing on North Sea oil rigs then taking off a few hours later – here’s why – https://theconversation.com/thousands-of-flies-keep-landing-on-north-sea-oil-rigs-then-taking-off-a-few-hours-later-heres-why-265622