28-July Wings & Stings: London’s July Insect Spectacle

In the countryside, umbellifers are covered in soldier beetles and on rough grassland grasshoppers draw attention to themselves with their constant chirruping. Patches of brambles, nettles and hawthorn scrub are all good places to look for a wider variety of insects. To find them it may be necessary to sweep the grass with a butterfly net or tap branches to see what falls from the leaves. It is also worth occasionally lifting stones and looking under bark.

Flies

Horseflies and clegs were much more common in the past, and were called gadflies. This was because when cattle or horses heard them they would ‘gad’ i.e. rush around frenetically, trying to avoid being bitten. Botflies also caused horses to ‘gad’. These unpleasant flies first lay their eggs on the horse’s skin. The eggs then get transferred to the horse’s stomach, after being licked. Here they hatch and then attach themselves to the stomach lining, each growing up to twenty-five millimetres in length before passing out nine months later.

Warble flies were even worse. They laid their eggs on the legs of cattle. The larvae then burrowed into the skin, migrating internally to the gullet by late summer and then on to the back by the winter. Here they made a hole in the poor animal’s skin so that they could breathe. This lump was called a ‘warble’ and within it the larva would continue to feed on the live animal’s flesh until it eventually fell out. Once on the ground, it would then pupate. Stable flies are another fly that tend to bite horses. They look like broad houseflies and tend to be seen in and around stables as you might expect.

The main culprits that now bite humans are female mosquitoes, biting mainly at dusk and dawn. The common gnat Culex pipiens attacks birds and not humans, often causing caged birds kept in open windows to suffer badly. Biting midges or gnats (Ceratopogonidae) are easily confused with non-biting midges (Chironomidae) which swarm over patches of water at this time of year and are quite harmless. Mosquitoes that do bite can be recognised by their distinct buzzing sound prior to landing. Once they land, you can usually see their excessively feathery antennae and their angled back, which is never held horizontally.

You can also often see the sharp projecting lancet of other biting flies. In meadows, it is usually horseflies that are the main culprits. These include dunflies, breezeflies, gadflies and clegs. Some of these hum loudly betraying their presence. The cleg is greatly disliked as it inflicts one of the most painful bites and you cannot even see its biting mouthparts. Clegs are dull grey flies with mottled wings fond of living in damp meadows. Here their larvae suck the blood of earthworms. The adults prefer to bite humans, especially in thundery weather, hence their alternative name of ‘thunderflies’.

Then there are other tiny, harmless flies such as sweat flies which cause mild irritation alighting on our skin to inspect our sweat pores. Robberflies are also harmless to us, but have a fearsome aspect. They are sometimes noticed on picnics as they have a habit of sitting on gateposts looking for other insect victims. They have long, tapering bodies and their flight is almost too fast to be seen. Dungflies, bluebottles and greenbottles are all very common, and thankfully none of them bite. Ichneumon flies are not flies at all, but also look dangerous due to their long, needle-like ovipositors. They too are harmless to humans and sometimes get noticed around bright windows at night.

Hoverflies are very much a feature of the month. Many Londoners are fearful of them as they have the same black and yellow warning colours as wasps, but they differ in having no waist and no sting. They can, however, hover both backwards, forwards and even hold their position in the wind. They also make highly acrobatic darting movements, allowing them to be easily identified. Sometimes they are called ‘flower flies’ as they hover so much in front of flowers before feeding on their pollen and nectar. This makes them important pollinators as well as good pest controllers, as their larvae eat large numbers of aphids. Other hoverfly larvae live in stagnant water, mud, compost heaps, animal manure and even wasps nests.

There are in the region of two hundred species of hoverfly in London, living in a wide variety of habitats. Not all of them look like small, hovering wasps. Some are mimics of bees or wasps. There are also many immigrants.

One of the most handsome is Volucella zonaria. This is a large, orange and black hoverfly that looks not unlike a hornet and can reach a dizzying three and a half centimetres in length. They can sometimes be seen in swarms over the Thames estuary as they migrate south. Another impressive large species is Scaeva pyrastri which is easier than most to recognise as it has white crescent-shaped markings rather than the usual yellow or orange ones

Among the vast number of different hoverflies, there are others that are more easily recognised. Syrphus ribesii makes a distinctive whining sound. Rhingia campestris has an impressively large and dangerous-looking beak. Chrysotoxum cautum is identified by its very large, round abdomen and Volucella pelucens by its shiny, black bottom. Mostly, identification is difficult, especially if they are bee or wasp mimics. Volucella bombylans even comes in several different colour forms depending which bee it is mimicking. One or two have English names. Helophilus pendulus is called the ‘sun fly’ due to its habit of basking in the sun and Eristalis tenax the ‘drone fly’ as it looks so much like a honey bee drone.

Other flies include the inconspicuous saw flies. In this case the females have a ‘saw’ on the lower part of their abdomen which they use to cut into a stem or leaf before laying their eggs. They are common garden pests, attacking many different vegetables and fruits. There are many, many other tiny flies, which mostly go unnoticed by Londoners unless they reach such numbers they start to cover our clothes and skin, causing irritation. An astonishing range of these and other insects can be seen in places such as Windsor Great Park, Bushy Park, Bookham Common, Rainham Marshes, Wimbledon Common and Farthing Down.

One of the most pleasurable insect encounters in high summer is when glow-worms are seen, typically between 10 and 11 at night on warm summer evenings. Such encounters are now much rarer than they used to be but the mixed meadow and woodland areas around Biggin Hill are still a good place to look for them.

It is the wingless females of a beetle Lampyrys nocticuluca which belongs to the firefly family that we see glowing. Usually they are about a metre above the ground in the vegetation, the glow being designed to attract a winged male.