Woodland hosts a phenomenal number of flies, many of which are very attractive, some of which prey on other invertebrates and a few of which can bite humans painfully. St Mark’s-flies (Bibio marci, 11mm), given the name because they are usually seen around St Mark’s day (25 April), are by no means predators. Their larvae feed on roots and vegetable matter underground and they are valuable pollinators of fruit trees. However, 2005 saw a massive emergence of the species, which made it open season on them for predators.
The most active of these were empid flies, led by Empis tessellata (12mm), which are powerful hunters. They are less prone to cannibalism than robber-flies but a male finding a female feeding is on pretty safe ground as to his own safety when pairing.
The same, only more so, applies to one of the commonest robber-flies, found well into the autumn – the Kite-tailed Robber-fly Machimus atricapillus (14mm). These are cannibalistic but the pictured male had nothing to worry about there during a procedure which lasted more than 40 minutes.
Machimus atricapillus can catch almost any Diptera and many Hymenoptera and suck them dry, while Dioctria baumhaueri (12mm) is smaller but equally deadly. They hunt usually from shrubs on wood margins, specialising in Ichneumon wasps as prey.
The Golden-haired Robber-fly (Choerades marginatus, 12mm) is very much a southern species and one associated most strongly with ancient oak woodland. They have strong mandibles since records of prey taken include a leafhopper bug and beetles, among them a weevil.
The Common Awl Robber-fly (Neoitamus cyanurus, 15mm) is also found most often in ancient oak woodland and may be seen from May to October in good years. The name comes from the long ovipositor the female is equipped with.
The Yellow Dung-fly (Scathophaga stercoraria, 10mm) is not a robber-fly and can be seen swarming around the mammal dung on which their larvae feed. They are effective hunters of fair-sized prey, and when they have finished the scavenging a Scorpion Fly (Panorpa communis, 14mm) can move in, as happened with those pictured on this page.
These common flies, with the male having the end of the abdomen turned up scorpion style, will feed on almost anything from rotting fruit to bird droppings. They are related to Lacewings and, like them, prefer shade to sun. Scorpion Flies are Mecoptera whereas Snake Flies such as Phaeostigma notata (15mm) are Neuroptera. Their English name comes from the length of the neck and the female uses her long ovipositor to lay eggs in the bark of dead or decaying trees, where the larvae dine on beetle grubs.
Flesh-flies (Sarcophaga carnaria, 12mm) are also scavengers which breed in carrion or dung. The female does not lay eggs but live maggots.
The Stiletto-fly (Thereva nobilitata, 11mm) resembles a robber-fly but lacks the distinctive groove between the eyes. They too can scavenge.
Tachinid flies are not predators but parasites. One of the most frequently seen as well as most striking is Tachina fera (15mm), which is evident from April through to September. They lay their eggs on plants from where the larvae locate and enter host lepidoptera caterpillars.
Another tachinid fly, Eriothrix rufomaculata (8mm), is a less robustly built species seen in the summer, often around flowers on woodland margins and in gardens. They also parasitise moth larvae, but specific information about this is scarce despite the fly’s common occurrence. A third from the family, Phasia hemiptera (8mm), lays eggs on bugs, in particular the Forest Bug and Green Shieldbug.
One nationally scarce fly which I was lucky to find and photograph mating close to some ancient woodland is Megamerina dolium (12mm), a fairly long, dark fly with red legs which is associated with dead wood habitat. Larvae have been found under the bark of fallen trees.
Horseflies are unpopular due to the painful bite they can give but some of them have stunning looks on account of their colourful eyes. Chrysops relictus (13mm) is one example and a relatively common one. In contrast, Soldierflies cause us no problems and although some of the brightest are restricted to damp areas, streams and flushes others can be found in woodland and hedgerow. Sargus bipunctatus (10mm), with two obvious white spots on the face that give it the Latin name, is not too difficult to find.
Images © Jeremy Early. All rights reserved.