Order Diptera - True Flies

• Crane-fly
• Hover-fly
• Blow-fly or Bluebottle
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Small to moderate-sized insects in which the hindwings are reduced to club-shaped balancing organs or halteres, leaving only one pair of membranous wings. A few species are completely wingless, usually in association with parasitic habits. Eyes usually large, occupying much of the head. Antennae variable, sometimes long and thread-like or plumose, but more often fairly short and bulbous, with the terminal segments more or less fused to form a spur or bristle. Mouthparts in the form of a proboscis for sucking liquid food, and sometimes also adapted for piercing. Many flies resemble bees and wasps as a result of mimicry, but such resemblances are only superficial (in body shape and colour, for example) and close examination will reveal only one pair wings, indicating a true fly (bees and wasps have two pairs of wings). There is a complex metamorphosis, with 3-8 larval stages, depending on species, and a pupal stage. Larvae are legless maggots, with the head reduced and often retracted into the body (see below). The pupae of many Diptera remain enclosed within the last larval skin, which hardens to form a protective outer shell or puparium. The true flies make up a very large Order with somewhere around 90,000 known species, of which some 5,200 are found in the British Isles.

Typical legless fly larva or maggot. The much reduced head and mouthparts are at the pointed end (facing to the right in the illustration).

The flies have exploited a very wide range of food materials, from decaying plant or animal matter on the one hand to nectar or blood on the other, and the Order as a whole is of considerable economic importance. Species that feed on decaying matter perform a useful scavenging role in the re-cycling of organic nutrients, others are useful predators or parasites of aphids and other plant pests, while many flower-feeding species are valuable pollinators. A number of flies are themselves agricultural pests in their larval stages and sometimes cause severe crop losses, but it is for direct attacks on man and his livestock that flies are most important. Blood-sucking flies are found in many families and they carry several dangerous diseases, including malaria, sleeping sickness, yellow fever and elephantiasis. Veterinary pests include a number of species whose maggots eat away or burrow into the flesh of domestic sheep and cattle, causing the condition known as myiasis.

Description. Adult 25-30 mm long, coloured yellow-grey. Abdomen of female pointed, that of the male blunt and slightly swollen. Larva up to 50 mm long, grey-brown and maggot-like, with a tough 'leathery' cuticle.

Biology. Found in gardens and farmland. Adults mainly fly at night and often attracted to lights. The larvae, commonly known as Leatherjackets, live in the soil and feed on plant roots. They sometimes become a serious threat to farm and garden crops, and often cause damage to grassland and lawns. Usually only one generation a year, with adults emerging in autumn.

Distribution. All the temperate parts of Europe, including the British Isles, and extending into the western parts of Asia.

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Adult female

Description. Adult about 10 mm long, mainly black with yellow bands on the abdomen. Larva up to 15 mm long, pale greenish-brown with darker markings; somewhat flattened and slug-like with short lateral outgrowths on each segment, but otherwise a typical maggot, tapering towards the head-end.

Biology. Adults are strong day-time flyers capable of hovering. They frequently visit flowers to feed on pollen and nectar. Larval stages are active predators of aphids and other small, plant-sucking insects. One or more generations each year depending on weather conditions. These are beneficial insects, useful as pollinators in the adult stage and as natural enemies of plant pests in the larval stages.

Distribution. Widespread throughout Britain and Europe.

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Adult fly resting on a leaf

Description. Adult about 9-14 mm long, body with stout bristles, dark metallic steel-blue or purplish-blue in colour. Larva up to 18 mm long, greyish-white in colour and a typical maggot, tapering towards the head-end.

Biology. Adults mainly diurnal and make a loud buzzing noise when in flight. Feed on nectar and carrion juices. Frequently enter houses and other buildings during summer in search of meat or fish on which to to lay their eggs. Carrion and other decaying materials are the main larval foods. Maggots reared commercially as live fish bait and pet food.

Distribution. Throughout Britain and Europe, with some species found worldwide.

Adult fly resting on a leaf