SMALL-HEADED FLIES Family Acroceridae Identification: Appearance distinctive: head very small and attached low on thorax, the body appearing humpbacked; calypters very large. Venation often reduced.

Acrocerids are medium-sized to small and are rather rare. Some species have a long slender proboscis. Larvae are parasites of spiders.

HILARIMORPHID FLIES Family Hilarimorphidae Not illus. Identification: Third antennal segment oval, with a short 2-segmented style. Tibiae without apical spurs. 4 posterior cells and no closed discal cell.

Three very rare species are known from the U.S. They have been taken from New England to the West Coast.

STILETTO FLIES Family Therevidae Identification: Medium-sized, usually grayish flies, with abdomen somewhat tapering. 3rd antennal segment slightly elon-gatedj often with a short terminal style. 5 posterior cells, the 4th sometimes closed.

Therevids resemble some robber flies (Asilidae), but differ in having the vertex flat or slightly convex (hollowed out in robber flies). They are relatively uncommon, and are usually found in open areas. Larvae occur in soil or decaying materials and are predaceous.

FLOWER-LOVING FLIES Family Apioceridae Not illus.

Identification: Similar to Therevidae but larger, and Mi curves forward and ends in front of wing tip.

This is a small group of rare flies occurring in arid regions of the West and usually found on flowers.

WINDOW FLIES Family Scenopinidae

Identification: Moderately robust flies somewhat smaller than a House Fly, and usually grayish or blackish. 3 posterior cells. Mi+2 ends in front of wing tip.

Window flies are so named because some are occasionally found on windows. They are relatively rare. Larvae usually occur in decaying wood or fungi; most are predaceous, and feed on a variety of insects.

ROBBER FLIES Family Asilidae See also PI. 13

Identification: Top of head hollowed out between eyes; 3 ocelli. 3rd antennal segment usually elongate, often bearing a short terminal style. Body varies from very hairy to nearly bare, but face usually bearded.

Robber flies are common insects, 5-30 mm., with legs and thorax relatively large. Most are relatively bare, with a long abdomen that tapers posteriorly; some are robust and hairy, and

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