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LongLeggedFly - (Photo credit: Charles Ray, Auburn University, Bugwood.org)

If you see long-legged flies in your garden or yard, don’t grab insecticide. These beneficial predators help reduce many insect pests.

When gardening, pulling weeds or visiting plants in your yard and landscape, you may encounter long-legged flies that dash from leaf to leaf, scurry about on plants, or even “dance” on leaves in the sunlight.

Long-legged flies are beneficial predators both as adults and larvae. They feed on a variety of small, soft-bodied arthropods, including other flies, thrips, aphids, spider mites, springtails, leafhoppers, whiteflies, small caterpillars, and even termites. Larvae of some long-legged flies eat other small arthropods in soil, while others are believed to be scavengers.

Long-legged flies pose no threat to humans as they do not bite or spread diseases. Plus, they prefer to remain outdoors, so it is unlikely you will find long-legged flies in your home.

Identification

Long-legged flies are members of the Order Diptera (true flies) and the family Dolichopodidae. More than 1,300 species of varying appearance and biology live in North America. Most are small with a metallic cast to their body and are slender in shape. Their size ranges from 1 mm to 9 mm.

Adult flies are easy to recognize for characteristics that differentiate them from other flies, such as metallic green-bottle flies and blowflies. They have metallic green, blue, red, copper, or gold body coloration, long and slender legs, a small and slender body, and one pair of clear wings that may be marked with dark spots or bands near the wing tips.

Crane flies are another common fly with long legs, but they are large (7 to 35 mm) with elongated wings (wingspan about 10 to 65 mm) and elongated legs that easily fall off. They are pale brown in color and very weak fliers. Because they look like oversized mosquitoes, they have wrongly been called
“mosquito hawk.”

Larvae of long-legged flies are maggots that develop in soil, rotting organic matter, or under bark. They pupate in cocoons made up of soil particles glued together.

Behavior

Long-legged flies are excellent fliers but usually move short distances, such as from leaf to leaf when disturbed.

Adult flies often are seen in a characteristic predatory posture, standing high on their legs on vegetation or other objects. They run about leaves in search of prey.

Some species of long-legged flies even walk on the surface of still water searching for mosquito larvae to eat.

Males of many long-legged fly species exhibit flag- like appendages on their front legs and/or modified antennae. These are used for attracting females during an elaborate, unique slow-motion cycle-walking courtship dance.

Adult flies can be seen carrying prey during flight. They are secreting digestive juices into the prey that allows them to feed on the liquefied contents.

Habitats

Long-legged flies occur in a wide range of habitats, preferably in wet areas such as near water margins and in meadows, woodlands, orchards, vineyards, and gardens.

Adult female flies typically lay eggs in moist soil and sometimes under tree bark. Larvae develop through several stages (instars) in soil ranging from moist to wet, under tree bark or algal mat, or in tree holes. Pupae occur where larvae live. You will likely encounter long- legged flies when they reach their adult stage, which typically starts in the spring and lasts through the fall.


Peer ReviewXing Ping Hu, Extension Specialist, Professor, Entomology and Plant Pathology, Auburn University

New July 2021, Benefits of Long-Legged Flies in Gardens & Yards, ANR-2791

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