You can be forgiven if you do not really think about gliders. They are confused with wasps or bees, but are overlooked in discussions about the decline of pollinators in favor of their more familiar appearance. Many of us do not really know what gliders are. What are they doing?
Gliders are a family of flies known as Syrphidae (they are also called sirphid flies) and as their name suggests, they are often seen hovering around flowers and between trees. While completely harmless – they are incapable of stinging – some mimics who have evolved to look like a specific bee or wasp to scare off predators seem to be more threatening than they really are. Others are much simpler, tiny and black, and are rarely noticed.
Organic gardeners know gliders as natural predators of insect pests such as greenflies and blackflies, 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 moist habitats to hatch and lay eggs in mud or stagnant water. You may have encountered “rock tail mowers” in your water butt, compost heap or pond. Are you terrified? It’s nothing more than baby gliders. It’s hard to believe such ugly ducklings can turn into things of incredible grace and beauty, but they do.
As pollinators, adult gliders are unsung heroes. Like bees, they eat nectar and pollen, but they can travel much greater distances and thus pollinate a greater variety of plants, including isolated plants. They do not do the work of bees, but neither do the work of gliders: the world needs both.
In the food chain, gliders are at the very bottom. Many are migratory, fly long distances in large groups, and are an essential source of food for migratory birds, such as swallows. And yet, like bees and other pollinators – indeed, most wild things – gliders are declining.
In April, a study of glider numbers in a remote Dutch forest was published in the Royal Entomological Society journal Insect Conservation and Diversity. Its author, ecologist Aat Barendregt, counted gliders along the same three-kilometer route for 40 years. It was the first time that these pollinators had been counted so consistently and for such a long time in a single place.
His findings were bleak: in 2021, on average, 80 percent fewer individuals and 44 percent fewer species were counted than when Barendregt began counting in 1982. The forest is relatively untouched, so the usual human interference of pesticides and habitat loss could not be responsible. Rather, the causes lie firmly at the foot of the greatest human intervention of all: climate change. Barendregt mentions acid rain, nitrogen deposition (more nitrogen in the atmosphere) and changes in weather patterns as probable causes for the bleeding of Holland’s gliders.
Do British gliders look as much like those in Holland? I asked the UK’s leading glider expert and organizer of the national glider survey scheme, Roger Morris. It is complicated, he says, because “in the UK there is no comparable data”. Records up to and including the 1980s involved museum specimens, while those of the 1990s and beyond included photographs.
“Gliders are very difficult to spot,” Morris says. “For some species you have to kill the monster and look at the male genitals. Most recorders do not do that. ”
This means, he suggests, that some of the rarer and smaller species may be overlooked, while some of the more common species may be over-registered. “This is not to say that gliders are not declining – that’s clear – but the data is not consistent and you need to deal with any decline with an element of caution.”
However, Morris can give me a general picture of British gliders. They are certainly 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 declining,” he says – although he urges me to be careful with this data . “In Scotland, it’s a different story, with numbers possibly even increasing.”
Scotland, it seems, is the place to be for much of our wildlife these days, with butterfly and bee experts constantly reporting that new species are emerging – presumably traveling north due to climate change.
So is climate change affecting British gliders? “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 recover quickly. But if those populations are knocked out year after year, you will gradually reduce power.
“We have had the 10 warmest years on record and the 10 driest years on record for the past 20 years. It will affect the humidity of habitats such as forests, but also soil conditions – if you are a glider that hatches in mud and that mud dries out and turns into cement, you are dead. ”
The Southeast can therefore do the worst for gliders because it is so dry. While I was typing from my home office in Brighton, we did not rain for 21 days. Long gone are the April moods that our gardeners have relied on for healthy seedling growth. The ground is patched and I worry about the hedgehogs and birds that rely on shrubs to eat and feed their young, as most will retreat deep into the ground or perish in the drought-like conditions.
But I can at least recycle bath water in my garden to keep it moist. I can keep trees hydrated and flowers that produce nectar for bees; leaves lush for caterpillars and those who eat them. It is more difficult to do this in nature.
Can gardens then be important for gliders? “Sure,” Morris said. “But we have to do more than plant flowers. We have to help them breed, and part of helping them breed is to maintain relative humidity levels. ”
We know some gliders lay eggs on aphid colonies, so let’s start by being friendlier to aphids. We also know other species lay eggs in muddy ponds, stumps and ponds.
“Hoverfly lagoons are fun and can be good for some species,” Morris says. “Put a few twigs in the bottom of a bucket, let it fill with rainwater and you will find species such as Myathropa florea (the bat glider) that breed in it.
“But we must also look at reducing hard surfaces such as patios and paving; let more plants grow. If you cut down a forest, you will reduce humidity. Add more hard surfaces and you will further increase heat and decrease humidity.
“Finally, if you want to help gliders, you need to grow more.”
Five Easy Ways to Help Beneficial Garden Insects
- Be kinder to aphids. Some gliders lay eggs on aphid colonies, so letting aphids stay on plants will mean more food for gliders
- Increase the humidity in the garden by using gray water (from your sink or bath) to water the garden during periods of drought
- Grow more plants: cover every wall, every fence with climbing plants and see how many more trees and shrubs you can add
- Reduces hard surfaces such as walkways, decks and plastic grass, which increase heat and reduce humidity
- Make a glider lagoon – put a few twigs in the bottom of a bucket and let it fill with rainwater to encourage species like Myathropa florea (the bat glider).