This year, we really want to familiarize our readers with beneficial flies! After learning about syrphids, blow flies, and predatory gall midges, we are going to end the season on long-legged flies (Figures 1 and 2)). Unlike the other species we have discussed this year, the family of long-legged flies (Dolichopodidae) contain numerous species which are predators in the larval and adult stages. While this family of flies is understudied, enough evidence has been collected to conclude that they are predators that contribute to pest management in many of our agricultural systems. They feed on soft-bodied pests like aphids, mites, springtails, leafhoppers, whiteflies, beetle larvae, and more! As mentioned, there are several species present in our agricultural landscapes. The most recognizable feature of these small flies (1-9mm), besides their long legs relative to their body size, is that many are metallic in color, including green, blue, or gold.
Figure 1. Front view of a long-legged fly (Photo by John Obermeyer).
Figure 2. Top view of a long-legged fly. Notice the iridescent coloring (Photo by John Obermeyer).
Like all other flies (Order Diptera meaning two-wings), long-legged flies undergo complete metamorphosis (egg-larva-pupa-adult). Adults can be found throughout the day flying around your crops, sometimes briefly resting on a leaf, but are easily disturbed and move a short distance. Often, you can see them in flight with their captured prey! The adults lay eggs in the soil where they hatch, and the larva feed on soil-dwelling invertebrates. They remain in the soil while they pupate, and when the adult emerges, they take to the sky. Adults feed by cutting a small hole in the body cavity of their prey and then ingesting the liquified contents of the body cavity.
To promote the establishment and colonization of long-legged flies on your farm, provide shaded and moist areas. The adults prefer to lay eggs in moist soils and decaying organic matter. Keep your eyes out for these small, flashy predatory flies as we wrap up harvesting for the season. They are not harmful to humans and quite cute, in my opinion.