Briefly - before getting down to the flies …
After twice hearing brief “Oh Canada ... etc” calls in recent days we finally confirmed the first White-throated Sparrow of the season visiting the garden as tea was being poured early this morning. The year is moving along as it should.
Now … on to the Flies:
Beetles, butterflies and moths which I covered in the first two weeks of this venture, are often rather attractive insects … not quite so much so in the case of many insects of the order Diptera which I briefly introduce today. As the name, Diptera, indicates the distinguishing feature of flies is that they have only a single pair of wings. There are several other insect species with common names that include the word “fly”, but only the two winged species are true FLIES. If you can see more than two wings then what you have is not a fly.
But “Flies?” I can almost hear you cry? “I’ve got far nicer, more interesting things to enjoy looking at whilst out walking”. I can almost sympathise … but imagine yourself bending over to admire a flower when a bee lands on it. You’d be pretty pleased and hopefully want to put a name to it. Well, the fly that landed on the second flower was interesting too. Our world would be a sad state were it not for flies - might as well get to know them better.
These are the main features of all flies … it’s what makes them flies and not some other insect.
Despite being very, very common as a group and there being high numbers of individuals and species, over 160 000 described species and likely many more are awaiting discovery, they are not always as easy to identify as are some other groups of insects. In part that has much to do with their often relatively small size and also the simple fact that the distinguishing feature between two similar species may be impossible to see without the use of a laboratory equipped with excellent optics. It’s easy to shudder at the thought of flies, who loves a House Fly for example, but some species are beneficial. For example as pollinators of flowering and fruiting plants - not all of that work is done by bees. Then we have the maggots of some Hover Flies (Fruit Flies if you live this side of the Atlantic) that feed on aphids, reducing numbers of those pests while the larvae (maggots) of more than a few species are parasitic, feeding on moth caterpillars, beetle grubs, and other pest species.
Flies exhibit an extraordinary range of life histories, morphologies, and behaviors - from aquatic larvae, to parasites, to nectar feeders.
Some of the principle groups of flies are these:
House Flies, Bluebottles etc - Houseflies possibly originated in the Middle East, and spread around the world as a commensal of humans. Adults are gray to black, with four dark, longitudinal lines on the thorax, slightly hairy bodies, and a single pair of membranous wings. Bluebottles, which in many ways look similar (and there are Greenbottles too) - appropriately named Calliphora vomitoria 😉 - play a role in pollination but can also carry diseases due to their feeding habits on rotting flesh and waste.
Crane Flies, Family Tipulidae. More than 10,000 species in the world, are large and long-legged, resembling and sometimes mistaken for mosquitoes. Commonly known as ‘Daddy Longlegs’ they should not be confused with the superficially similar and equally long-legged Harvestman spiders. Although they resemble large mosquitoes, adult crane flies do not bite or feed on blood. Their primary ecological role is as decomposers during the larval stage and as a food source for birds, amphibians, and other predators.
Tachinid Flies, Family Tachinidae. A large Family of flies, with larvae parasitic on other insects and so often beneficial. One species that gardeners, at least, will take to their hearts is over 160 000 described species and likely many more awaiting discovery. These are the principle parasite of the infamous Japanese Beetle. The female fly glues her eggs onto young adult Japanese beetles. Over the course of about a week, the eggs hatch into fly larvae, which then burrow into the beetle’s body to eventually consume and kill it. You can identify a Japanese Beetle that is affected by looking for the eggs which appear as large white dots behind the head and if you see affected beetles perhaps consider not killing them, as left to be killed by the fly larvae they then become a breeding ground for more flies, all of which help to reduce the beetle population … and that’s a good thing, a very good thing. Overall, Tachinid flies are beneficial, parasitoid insects that play a key part in controlling other insect populations.
Hover Flies (also known as Flower Flies), Family Syrphidae. Often brightly coloured in yellows and black, and sometimes mimics of small bees or wasps. Many are common and none of them are at all a nuisance.
Adults are frequent visitors to a wide variety of flowering plants and contribute significantly to pollination. Their ability to hover allows them to access flowers with complex morphologies. Predatory larvae of some species help to suppress populations of aphids, scale insects, and other agricultural pests, reducing the need for chemical insecticides … bonus marks for that.
Bee Flies, Family Bombyliidae. This Family includes many parasitic insects. Like Hover Flies they can visually mimic bees and wasps, having hairy bodies, banded abdomens, and coloration that mimics bees (often black and yellow or orange) which deters predators. Not everything striped yellow and black can sting, not everything with a furry body is a bumble bee.
Robber Flies (Assassin Flies), Family Asilidae. These flies are predators that hunt and feed on other insects. Adults capture prey in flight, using strong, spiny legs and a powerful, piercing‑sucking mouthpart (proboscis).They are the third most diverse group of flies, with more than seven thousand species already identified and countless others yet to be discovered. They are beautifully adapted to their role - many species have a stout, bristly appearance with a characteristic “bearded” face that protects the head during struggles with prey. They also benefit from excellent vision with large compound eyes that provide acute sight, helping them spot and ambush prey from perches such as twigs, rocks, or foliage.
To look at they are distinctly bristly flies with a short, stout proboscis enclosing a sharp, sucking hypopharynx. The name "robber flies" arises from their aggressive predatory habits; they feed mainly or exclusively on other insects; most species wait in ambush and catch their prey in flight.
… and, of course , who could ignore the many species of the ever-lovely Mosquitoes (Culicidae spp) which suround us. Despite being a nuisance to people there are very important as essential food for birds. In fact, a major reason for the decrease in numbers of flycatching birds such as Swallows and Purple Martins has been because mosquitoes have been too well controlled.
Mosquito larvae are important in freshwater ecosystems, consuming algae and bacteria, and serving as prey for fish, amphibians, and predatory insects. Adults provide a food source for bats, birds, and other insectivores. Sadly, some are vectors for numerous pathogens such as malaria … not around here however. I don’t expect any readers will need a photo, but to complete the page let’s have one anyway.
Next Week - “True” Bugs
Really enjoyed this write-up — especially the reminder that flies aren’t just nuisances but key players in pollination, decomposition, and even natural pest control (the Tachinid fly example was excellent).
In my line of work we often see the “problem side” of insects, but it’s just as important to recognize the balance they provide. Responsible pest management isn’t about wiping species out — it’s about protecting health and property while respecting the role insects play in the bigger ecosystem. Your piece captured that balance really well.
Excellent article! Flies are much maligned and misunderstood. Hoverflies and bee flies are among my favourite groups of insects. (We have about 250 species of hoverfly in the UK and I've seen and identified around 30 of them in the wild, though some I can't identify right down to species level).