Black Robber Fly ?
July 15, 2009
This is a common fly in my garden this summer. There may be as many as five of them that have set up territories throughout my strawberries, squash, and tomatoes. It resembles a robber fly in the way it perches on vantage points and quickly flies away when disturbed in the slightest. It sometimes seems aggressive and will even investigate me when I attempt to photograph it. This is a large black fly that I suspect is over an inch in length and has orange, lateral, very round, spots, one on either side of the abdomen near the thorax. Some of the individuals have light yellow spots and others have brighter orange spots. I have never seen one with prey, as I do the other recognizable species of robber flies in the garden. This picture was taken in mid-July during some of the hottest days of summer in Oklahoma. Rain has been sparse and the ground is very dry except around the garden that is regularly watered and attracts several species of insect.
This is a Mydas Fly, Mydas clavatus. According to BugGuide: “I have seen adults (males?) of this species taking nectar from several sources in Durham, North Carolina. I have seen a female ovipositing in a dead maple stump. Later, I found this stump was full of carpenter ants and large beetle larvae (probably Odontoaenius disjunctus). I have not observed the adults taking prey on the wing. Sources vary on the feeding habits of adults. Most say the adults are predatory, but this may be incorrect. Perhaps this is due to confusion with the somewhat similar Robber Flies (Asilidae)?” BugGuide also indicates that male Mydas Flies engage in Hilltopping, which Wikipedia explains as a mate-location behavior where “Males of many butterfly species may be found flying up to and staying on a hilltop – for days on end if necessary. Females, desirous of mating, fly up the hill. Males dash around the top, competing for the best part of the area – usually the very top; as the male with the best territory at the top of the hill would have the best chance of mating with the occasional female, who knows the ‘top male’ must be strong and thus genetically fit. Many authors consider this as a form of lekking behaviour. Many butterfly species including swallowtails, nymphalids, metal-marks and lycaenids are known to hill-top.”