The British hoverfly is in trouble – and yes, it affects you

You could be forgiven for not really thinking about hoverflies. They get mistaken for wasps or bees, but are overlooked in discussions about the decline of pollinators in favor of their more famous lookalikes. Many of us don’t really know what hoverflies are. What do they do?

Hoverflies are a family of flies known as Syrphidae (they are also called syrphid flies) and as their name suggests, they are often seen hovering around flowers and among trees. While completely harmless – they are incapable of stinging – some are mimics that have evolved to resemble a specific bee or wasp to deter predators, so look more threatening than they really are. Others are much plainer, tiny and black, and are rarely noticed.

Organic gardeners know hoverflies as natural predators of insect pests such as greenfly and blackfly, along with other sap-sucking insects such as mites and thrips. While the adults feed on nectar and pollen, the females of some species lay their eggs near aphid colonies so that their larvae can devour them. Other types lay eggs in bee or wasp nests, while some rely on damp habitats to breed and lay eggs in mud or stagnant water. You may have come across “rat-tailed maggots” in your water butt, compost heap or pond. Are you horrified? These are nothing more than baby hoverflies. It’s hard to believe such ugly ducklings can turn into things of incredible grace and beauty, but they do.

As pollinators, adult hoverflies are unsung heroes. Like bees, they eat nectar and pollen, but they can travel much greater distances and therefore pollinate a greater range of plants, including isolated plants. They don’t do the work of bees, but neither do bees do the work of hoverflies: the world needs both.

In the food chain, hoverflies are right at the bottom. Many are migratory, flying huge distances in large groups, and are an essential source of food for migratory birds, such as swifts. And yet, like bees and other pollinators – indeed, most wild things – hoverflies are declining.

In April, a study of hoverfly numbers in a remote Dutch forest was published in the Royal Entomological Society journal Insect Conservation and Diversity. Its author, ecologist Aat Barendregt, had spent 40 years counting hoverflies along the same three-kilometre route. It was the first time these pollinators had been counted so consistently and for such a long time at a single location.

His findings were bleak: in 2021, an average of 80 per cent fewer individuals and 44 per cent fewer species were counted than when Barendregt started counting in 1982. The forest is relatively untouched, so the usual human interferences of pesticides and habitat loss could not have been responsible. Rather, the causes lie firmly at the feet of the biggest human interference of them all: climate change. Barendregt cites acid rain, nitrogen deposition (more nitrogen in the atmosphere) and changes in weather patterns as likely causes for the haemorrhaging of Holland’s hoverflies.

Are British hoverflies suffering as much as those in Holland? I asked the UK’s leading hoverfly expert, and organizer of the national Hoverfly Recording Scheme, Roger Morris. It’s complicated, he says, because “in the UK there’s no comparable data”. Records up to and including the 1980s involved museum specimens, while those from the 1990s and beyond involve photographs.

“Hoverflies are very difficult to record,” says Morris. “For some species you need to kill the specimen and look at the male genitalia. Most recorders don’t do that.”

This means, he suggests, that some of the rarer and smaller species are overlooked, while some of the more common species may be over-recorded. “That’s not to say hoverflies aren’t declining – they clearly are – but the data isn’t consistent and you have to treat any decline with an element of caution.”

Morris is able to provide me with a general picture of British hoverflies, however. They certainly are declining, at least in most parts of Britain: “In the South East the situation is particularly bad, with between 50 and 70 per cent of species in decline,” he says – though he urges me to be cautious with this data . “In Scotland it’s a different story, with numbers potentially even increasing.”

Scotland, it seems, is the place to be for much of our wildlife these days, with butterfly and bee experts recording new species turning up all the time – thought to be traveling north because of climate change.

So is climate change affecting British hoverflies? “Some of us call it death by a thousand droughts”, he says. “One drought will have an effect on populations for a year but most species will quickly bounce back. But if those populations are knocked out year after year, you’ll gradually reduce strength.

“In the past 20 years we have had the 10 hottest years on record and the 10 driest years on record. These will affect humidity of habitats like forests, but also soil conditions – if you’re a hoverfly that breeds in mud and that mud dries out and turns into cement, you’re dead.”

The South East, therefore, could be faring worst for hoverflies because it is so dry. As I type from my home office in Brighton, we haven’t had rain for 21 days. Long gone are the April showers we gardeners relied on for healthy seedling growth. The soil is patched and I worry about the hedgehogs and birds that rely on grubs to eat and feed their young, as most will retreat deep into the soil or perish in the drought-like conditions.

But at least I can recycle bath water onto my garden to keep it moist. I can keep trees hydrated and flowers producing nectar for bees; leaves lush for caterpillars and those that eat them. It’s harder to do that in the wild.

Can gardens be important for hoverflies then? “Certainly,” says Morris. “But we need to do more than plant flowers. We need to help them breed, and part of helping them breed is to maintain relative levels of humidity.”

We know some hoverflies lay eggs on aphid colonies, so let’s start by being nicer to aphids. We also know other species lay eggs in muddy puddles, water butts and ponds.

“Hoverfly lagoons are fun and can be good for some species,” says Morris. “Put a few twigs in the bottom of a bucket, let it fill up with rainwater and you’ll get species like Myathropa florea (the batman hoverfly) breeding in it.

“But we also need to look at reducing hard surfaces such as patios and paving; have more plants growing. If you cut down a bush, you will reduce humidity. Add more hard surfaces and you will further increase heat and reduce humidity.

“Ultimately, if you want to help hoverflies, you need to grow more.”

Five easy ways to help beneficial garden insects

  1. Be nicer to aphids. Some hoverflies lay eggs on aphid colonies, so letting aphids remain on plants will mean more food for hoverflies
  2. Increase garden humidity by using gray water (from your washing up bowl or bath) to water the garden during periods of drought
  3. Grow more plants: cover every wall, every fence with climbers and see how many more trees and shrubs you can add
  4. Reduce hard surfaces such as paths, decking and plastic grass, which increase heat and reduce humidity
  5. Make a hoverfly lagoon – put a few twigs in the bottom of a bucket and let it fill up with rainwater to encourage species such as Myathropa florea (the batman hoverfly)

Related Posts

George Holan

George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.

Leave a Reply

Your email address will not be published. Required fields are marked *