Wild Ideas: The fierce predator with little red feet   

Despite its name, the color of a red-footed cannibalfly’s feet can vary from bright red to orange or tan.
Despite its name, the color of a red-footed cannibalfly’s feet can vary from bright red to orange or tan. Pam Owen

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.

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. 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, 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.

Red-footed cannibalflies will not only prey on large insects such as this coreid bug, as well as bumblebees and dragonflies, but are also known to go after hummingbirds.
Red-footed cannibalflies will not only prey on large insects such as this coreid bug, as well as bumblebees and dragonflies, but are also known to go after hummingbirds. Pam Owen

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 another order (Odonata), mate. (See a shot of grounded red-footeds mating at the What’s that Bug website).

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 low-lying 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.

© 2016 Pam Owen

New video on creating frog ponds

A new video shows how to make a frog pond to attract anurans such as this wood frog.
A new video shows how to make a frog pond to attract anurans such as this wood frog. Pam Owen

Carol Heiser, habitat education coordinator at the Virginia Department of Game and Inland Fisheries, recently sent me an email about a new short video produced by the department, “How To Add a Frog Pond to Your Landscape.”

In watching the video, I was surprised and really happy to see Lou Verner, a retired “watchable wildlife” biologist at VDGIF, featured along with Carol. Lou was also a member of the Master Naturalist Statewide Steering Committee for the Virginia Master Naturalist Program. I met him when I was doing a lot of conservation work, including helping to form our local VMN chapter, Old Rag Master Naturalists.

Lou has always been a great guy to talk with about pretty much anything having to do with biology and ecology, and I still contact him when I have a thorny question about either. What I didn’t know is that he has made great frog ponds down at his place in King & Queen County. In about six and a half minutes, he and Carol cover the basics of making one of these, whether starting with a small, molded plastic liner or using flexible liners to create your own design. They also go over what to plant to keep the pond healthy and attract the insects frogs prey on. As noted in the video, you don’t need to add frogs — if you build it, they will come.

Carol suggests accessing the video from the department’s Facebook page, where viewers can post comments. The video is also available from the department’s “Virginia Is for Frogs” web page, which has a lot of other great info about our local anurans as well.

Pam Owen
About Pam Owen 343 Articles
Writer, editor, photographer, and passionate nature conservationist living in Rappahannock County, in the Blue Ridge Mountains of Virginia. Two favorite quotes: By E.O. Wilson, who coined the term "biodiversity," "Nature holds the key to our aesthetic, intellectual, cognitive and even spiritual satisfaction”; by Douglas Adams, “I love deadlines. I love the whooshing sound they make as they pass by.”