When I first started with Nebraska Extension, I received some very interesting phone calls. That’s a given seeing as I am an urban entomologist, here to respond to questions about critters that “bug” people in and around their homes. What was striking was the number of calls from individuals “calling to report a cow killer” as if I was the holder of the National Cow Killer Registry (I don’t believe one exists).
With a name “cow killer”, one can only expect that to report it upon sighting, right? My general response has been, “Not necessary, but thanks for thinking of me.”
The cow killer is a species of velvet ant, which is neither a murderer of cows nor an ant. This insect is in fact a wasp! The female cow killer, has no wings, so they look like an ant. The males look and fly like the wasp that they are, but are seldom recognized as being the same species. This is called an example of sexual dimorphism, where male and female members of the same species look very different. Nobody has ever called to report a male.
All velvet ants belong to the family Mutillidae, which possess a dense pile of hair of a variety of striking colors that serve as a warning signal to potential predators. They can be found worldwide, but in Nebraska, the cow killer ant, Dasymutilla occidentalis, is the most common. They are commonly found during the summer months wandering around the yard in urban landscapes around homes, but are also found in open areas like pastures.
The female cow killer ant is a large hairy, wingless wasp that resembles a worker ant. They can be up to 3/4-inch long with a black body with coarse, bright reddish-orange hair on the head, thorax and abdomen. The males are larger than females; possess dark brown wings and have different color patterns on its body. Both male and female velvet ants will produce a squeaking or chirping sound when alarmed, which is pretty neat.
Velvet ants are solitary wasps. Males fly in search of females to mate. The mated female will enter a ground nesting bee or wasp nest, and lay her eggs on or near the other insect’s larva. When the velvet ant larvae emerge from the eggs, they feed on the host’s larvae, killing them. This is why they are considered parasitoids. As adults, velvet ants feed on nectar (not cows or people or other insects).
Though the female cow killer cannot fly, it has many defenses. Besides bright warning colors and squeaking warning sound, they are quick movers, have a very strong exoskeleton and can release smelly odors. In addition, females are capable of delivering a very painful sting. Females alone have a large, retractable stinger, which is a modified egg-laying organ called the ovipositor. On the Schmidt’s sting pain index which ranks and describes insects based on one scientists evaluation of stinging insects, it is ranked 3 out of 4 (4 is most painful). Therefore, they can inflict an excruciating sting if handled or stepped on, which is why they are called cow killers. As far as we know, no cow has ever died from a sting. The sting may be painful, but the venom is not very toxic.
Despite their massive defenses, velvet ants are not aggressive and they will try and hide in leaf litter and mulch. If you see velvet ants around your home, no need to worry. Just leave them alone, and tell your children not touch. No control measures are necessary for the yard and they are not an indoor pest.
More information about velvet ants can be found through the following links:
Mutillidae identification key: http://entnemdept.ufl.edu/creatures/misc/wasps/mutillidae.htm