Most of us don’t tend to think of flies as being in any way noteworthy. Houseflies can certainly be an annoyance at this time of year. Because flies have taste buds on their feet, it is by walking all over our precious slice of cheesecake that they can decipher whether it is edible, hence the habit of trampling all over our food. In response we swat them, electrocute them, poison and curse them. But houseflies are far from the only flies, in fact there are over 3,300 different species of fly in Ireland alone. Here, as across the globe, flies collectively contribute a great deal to the healthy functioning of ecosystems, which in turn, are what sustain all of us.
Flies are differentiated from other flying insects by having two wings, hence the scientific name ‘Diptera’ (two-winged). For a fly to stay airborne and move forward, this single pair of wings beat around 200 times per second. The Diptera family is incredibly diverse, with over 240,000 known species. Aside from houseflies, there are crane flies, caddis flies, stoneflies, fruit flies, sand flies, dung flies, stiletto flies, fireflies, and many more. Relative to the human population, it is estimated that there are 17 million flies each person on earth. Impressive.
Flies have a baffling variety of life strategies and functioning roles in every ecosystem. Tens of thousands of different species of aquatic flies, spending most of their lives underwater, are the main food source for fish such as salmon and trout. Many species of fly decompose sludge, dung, and dead things; without them, we would be inundated with waste. But flies are also the most important pollinators after bees, a service that is rarely acknowledged.
If you like chocolate, it is flies you have to thank for the luxury. The tiny ‘chocolate midge’ fly pollinates the cocoa plants that we derive chocolate from. In the tropics where cocoa plants grow, the chocolate midge drinks nectar from cocoa flowers and transports pollen from one plant to another. Without these little flies, we would all be without chocolate chip cookies, dairy milk bars, the flake in your 99, or whatever your favourite form of chocolate is.
If you love a heather-clad hillside in late summer, that’s also thanks to flies. The gorgeous purple heather blossoms are pollinated tiny, specialist midges, also of the fly family. Heather is not only beautiful, but it is home to an array of specialist bugs and butterflies such as the heather ladybird and increasingly rare heath butterfly, as well as providing habitat for many upland and ground-nesting birds.
Hoverflies are a family of flies that are especially associated with flowers and are thus crucial pollinators in almost every type of habitat. Only solitary bees and bumblebees are more valuable than hoverflies as commercial pollinators, making hoverflies a crucial player in ensuring global food security, though bees seem to get all the credit for this service.
Hoverflies are active in the garden too at the moment, making them easy to observe. Here in Ireland, we have 180 different species of hoverflies, many of them mimic bees and wasps. The Drone fly, for example, is a hoverfly that looks almost exactly like a honey bee. Other hoverflies imitate the many species of solitary bees we have in Ireland. Their hovering flight is the tell-tale sign that these are flies rather than bees or wasps.
If you can look closely, observe the number of wings. Bees and wasps have 2 pairs of wings, but a hoverfly imitating a bee or a wasp still only has 1 pair of wings. Because these flies aren’t in any way dangerous, it makes sense for them to imitate a more threatening insect, such as a stinging bee or wasp. Looking dangerous can be almost as effective as actually being dangerous.
Having hoverflies in the garden can be a very good thing. The larvae of lots of hoverfly species, when tiny and without any wings at all, are avid consumers of aphids, otherwise known as greenfly or blackfly. Spraying the aphids with pesticides will in turn damage hoverfly populations, meaning less pest control and less pollination.
Swifts, swallows, house martins, and other avian acrobats that we so love, feed exclusively on flying insects, mostly flies. Without a plentiful supply of midges, hoverflies and other flies at this time of year, these birds would be unable to nourish the next generation transcontinental adventurers. As night falls, bats take over from swifts, swallows and housemartins in the insect easting shift. Their ultrasonic hunting has evolved especially to locate and catch midges, flies and other night-flying insects such as moths and caddisflies.
An entomologist named Vincent G. Dethier wrote a seminal work on flies in 1962, called ‘To Know a Fly’. In it, he states “Like taxes, the fly is always with us.”
I'll add to that, like taxes, flies are necessary for the healthy functioning of society, though that doesn’t necessarily mean we always appreciate or celebrate them.