Mydas flies are true flies belonging to Order Diptera (meaning two-winged) and Family Mydidae. While the number of species classified within Mydidae is small in number (fewer than 400 species), this family of insects occurs worldwide. Members of this family are commonly referred to as mydids. A total of 51 species are reported to occur in North America and most species occur in the western portion.
Most mydid species are strikingly handsome, elongate flies that are of medium to large size. Adult mydids occupy a wide variety of habitats but they are more commonly seen in open country. They are fond of hot, sandy habitats and can be found resting on bare ground. Females dig into the soil with the tip of the abdomen to lay eggs.
Mydas chrysostomus is second mydid species that we have collected (albeit by digital images) thus far in the Galveston-Houston region. The specimen shown was photographed at Mercer Arboreum (just north of Houston). As is characteristics of many mydids, Mydas chrysostomus has a sparsely pilose body (covered with hairs, especially fine soft ones) and bares a strong resemblance to wasps. However, after closer inspection, we noticed that it had two wings (a characteristic of true flies in Order Diptera) instead of four wings that characteristic of wasps, hornets, yellow jackets and other winged members of Order Hymenoptera, Family Vespidae.
Mydas chrysostomus also bears a superficial resemblance to Asilidae (robber flies) but are distinguished by long 4-segmented, clubbed antennae that project forward (robber flies typically have short antennae that are barely visible) and the venation pattern in their wings. Mydas flies have jet-black bodies, a wingspan of approximately 2 inches and golden-orange spots on their legs. Mydas flies also have a striking orange-yellow colored half-band on the abdomen.
Compared to the other legs, the hind pair of legs of a mydas fly is longer and stouter. The hind femur (one of the six components of an insectís leg) is enlarged and bears numerous spines on the lower surface. The hind tibia (another of the six components of an insectís leg which adjoins the femur) has an apical spur or bristles.
A number of authors have discussed the possibility that adult mydids prey upon other insects but there is little evidence for this habit. Adults most probably feed on nectar and pollen from flowers and adults with atrophied mouthparts may not feed at all. While information on the feeding habits of the adult stage is sparse, the larvae are known to be effective soil-dwelling predators. They have well-developed mouthparts to prey on other soil-dwelling insect larvae, especially on coleopteran (beetle) larvae (including white grubworms and other larvae of beetles).
The pupae as a resting stage remain a few inches below the surface in the soil. With the help of their strong spines, the pupae make their way to the surface. Here they remain half-buried until the hottest hours of the day when the adult stage emerges. The onset of emergence is not fixed from year to year but depends on the weather and other conditions.
Mydas flies are infrequently encountered as the adult life span appears to be quite short, and little is known about their biology. While creditable information on the mydas fly is rather difficult to find, we know that two mydas fly species (Mydas chrysostomus and M. clavata) occur in our Galveston-Houston region and that the larval stages are beneficial.
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