A fierce predator with little red feet
Meet one small bug-eyed monster, the red-footed cannibalfly
Although many insects have wound down their reproductive activities, some are still going at it, or just getting started, including one small bug-eyed monster, the red- footed cannibalfly. Hearing loud buzzing around my head on a couple of occasions, I thought bees were fighting near my head only to turn around and see two large, hairy flies with an entirely different agenda on their minds. They were red-two footed cannibalflies ( Promachus rufipes), in the robber fly family ( Asilidae), working on producing next year’s generation.
Related to dragonflies, robber flies not only look fierce but are ferocious in their hunting. Also known as assassin flies, they often take on prey that are almost their size — or even bigger than they are. In trying to learn more about the fly’s reproduction, I ended up on the Hilton Pond Center for Piedmont Natural History website (hiltonpond.org/ThisWeek070901.html). Although the center is in South Carolina, many of the same species are found in Virginia’s Piedmont, and I’ve often found great information for this column there.
As the website’s “This week at Hilton Pond” blog for Sept. 1- 7, 2007, notes, “robber flies make up one of the biggest and most widely distributed insect groups in the world, with more than 7,000 species — some dating as far back as the Eocene Epoch (54.8 to 33.7 million years ago).” While I didn’t get much info on the red- footed’s breeding habits, I did find some testament to its ferocity.
Robber are among the few predators that are quick, strong and big enough to catch a hummingbird, with a few incidents circulating through several nature-related websites, including Hilton Pond’s. The red- footed cannibalfly, in the “giant robber fly” genus ( Promachus ), is 1- 1.25
inches long, about half the size of most hummingbirds. The blog describes accounts of hummers being nailed by this robber fly as well as one in the “bee killer” genus ( Mallophora), the beelzebub bee- eater ( Mallophora leschenaultia). Bees are a favorite prey of robber flies. The other common name for the red- footed cannibalfly is “bee panther.” Some robber flies in the Mallophora genus have actually evolved to mimic bees, enabling them to sneak up on their prey.
According to the website of the University of Florida’s entomology department (tinyurl.com/wi-uf-flies), robber flies grab their prey in flight, injecting their victims with saliva that has paralyzing and liquefying enzymes. “This injection, inflicted by their modified mouthparts (hypotharynx), rapidly immobilizes prey and allows digestion of bodily contents,” the site says. Although robber flies, like dragonflies, have no interest in us beyond perhaps using us as a perch occasionally, they have the equipment to inflict a nasty wound if not handled carefully, so are best left alone.
I was first introduced to red-footed robber flies a few summers ago when I found one feeding on a coreid bug, which was almost the same size as the fly, from a perch on one of the giant sunflowers I planted next to my house. I was really drawn to the fly because of the juxtaposition of its fiercer features — the hairy, tough, tiger-striped body, humped back, bulging black eyes and long, spined legs —against two mitten-like red “toes” at the end of its legs. The little mittens bely the whole bug-eyed monster look this fly is otherwise rocking.
Those long, strong legs also play a role in courtship, which happens around this time of year. Robber flies’ courtship behavior is far from romantic, with the male pouncing on the female “much like an act of prey acquisition,” according to the FL website. The pair I mentioned above that were buzzing around my head were in the process of the next reproductive step — copulating tail-to-tail, with the male and female genitalia interlocked. This is similar to how dragonflies, which are in the same order (Odonata), mate. (See a shot of grounded red-footeds mating at the What’s that Bug website, tinyurl.com/wi-cannibalfly).
Also like dragonflies, robber flies can mate while in flight. The next day I spotted another pair on my goldenrod. The male was on the back of a female, grasping her with his legs.
According to the UF website, female robber flies deposit their eggs on lowlying plants and grasses, or in soil, bark, or wood. Their larvae live in the soil or in various decaying organic materials and are also predatory, feeding on eggs, larvae or other soft-bodied insects. Robber flies overwinter as larvae and pupate in the soil. Pupae migrate to the soil surface, eventually emerging as adults. It takes one to three years for the fly to develop into an adult, depending on the species and environmental conditions. For more information about the many species of robber flies, including lots of photos, go to BugGuide.net (bugguide.net/node/view/151).