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Image Credits: Robber Fly sketch by Hannah Nadel in 'Rare Invertebrates of the South Okanagan' brochure. Photo by Okanagan Universtiy College. Order Diptera, Flies, are easily distinguished from other insects because they have only one pair of normal wings. The second pair, just behind the first, is represented by two knobbed organs, the halteres, used to stabilize the body during flight. Most flies have large compound eyes and mouthparts that are modified for piercing, lapping, or sucking fluids. Robber flies are common, swiftly flying predators, 5-30 mm long. Many have stout, spiny legs, a dense "beard" of bristles on the face, and a depression in the forehead between the compound eyes. Many species are important predators in grassland habitats. Megaphorus willistoni are squat little flies bristling with grey and yellow hairs, which give them an uncanny resemblance to leaf-cutter bees as they buzz from plant to plant, hovering here and there in search of prey.
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British Columbia
North America They live in the hot, dry grasslands and shrublands that remain and seem to prefer areas with many flowers, since this is where their favourite prey, small bees and wasps, abound. Rare invertebrates of the south Okanagan and Similkameen valleys such as this species are threatened not by direct exploitation, but by loss or degradation of their habitats. They are at risk because their ecosystems are at risk. The grasslands of the southern interior of the province are a valuable agricultural resource, and their rich soils have been ploughed and irrigated to produce tree fruits, grapes, and vegetables. Pesticide use has probably had a great impact on native insects living in around agricultural areas. As well, heavy grazing has altered the plant composition of grasslands, changing the invertebrate communities. The Robber Fly is effected by compaction caused by trampling by cattle. The massive diversity of invertebrate species in British Columbia makes it very difficult for entomologists to do a literature or collection survey to determine which species are endangered or threatened. Specialized, detailed surveys will be required for almost every species that is suspected of being endangered. Despite a general ignorance about invertebrate distribution, information is known about a number of species that are confined to threatened habitats of very limited extent in the Thompson-Okanagan valleys. Eggs are laid in a case-like mass on a dead plant stem; the larvae develop in the soil where they apparently prey on other insect larvae. Like all robber flies, they capture their prey in their bristly legs and kill it with toxic saliva injected through their short proboscis. The dissolved tissues are then sucked back up through the proboscis. Flies exhibit complete metamorphosis. The larvae of many species are soft, legless, and headless. They are called maggots and live in soil, decaying material, or as parasites of vertebrates, snails, or other insects. Related On-line Sites to Visit
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