PESTS & WILDLIFE — Cow killer ant: Wrongfully accused

Female cow killer ant, a velvet ant, can be up to 3/4-inch long. (Photo by Jody Green, Nebraska Extension in Lancaster County)
Female cow killer ant, a velvet ant, can be up to 3/4-inch long. (Photo by Jody Green, Nebraska Extension in Lancaster County)

By Jody Green, Extension Educator

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 it resemble an ant. The males look and fly like the wasp 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, emailed or brought in a male specimen for me to identify.

All velvet ants belong to the family Mutillidae, which possess a dense pile of hair in 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 often found during the months of July, August and September, wandering around the yard in urban landscapes around homes, but are also found in pastures, parks and recreational areas.

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 red and black patterns on its body. Both male and female velvet ants will produce a squeaking or chirping sound when alarmed or disturbed. This is a warning to leave them alone!

Cow killer 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 larvae. 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, people or other insects). Though the female cow killer cannot fly, it has many defenses. Besides bright warning colors (called aposematism) and squeaking warning sound, they are quick movers, have a very solid exoskeleton and can release smelly odors. In addition, females are capable of delivering a very painful sting. Females 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, hence the name 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 small children not to touch. No control measures are necessary for the yard and they are not an indoor pest. If there is concern about keeping them out of nearby buildings, practice pest exclusion techniques around the perimeter — sealing areas around and under doors, windows, gaps and holes around the foundation.