Photo by Okanagan Universtiy College. Distinguishing features 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 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. Distribution Map Red dots indicate specimen records or confirmed breeding sites. Only one specimen of this small robber fly has been recorded in Canada, just a few hundred metres from the International Boundary in the southern Similkameen Valley. 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.