A sting to kill a cow? Red velvet ant, a.k.a. cow killer, Dasymutilla occidentalis
Powerful jaws help the velvet ant defend itself.
Must have been a brave soul who corralled this red velvet ant in a drinking glass. Photo credit: Tracy
In a previous episode of Bug of the Week, we lamented the scarcity of swallowtail butterflies in our gardens. Swallowtails have been scarce, but in my flower beds, bumble bees have been rocking. Bumble bees build nests in the ground, often in the former burrows of chipmunks, or sometimes in the hollow of a fallen tree. One might think a carefully constructed subterranean nest defended by bumble bees would be a pretty safe place to raise young. Most of the time this is true, but not so when red velvet ants are in town. This gorgeous insect is not an ant at all. Ants are social insects ruled by one or more queens governing a caste system of workers. Velvet ants are wasps in the family Mutillidae, a large group of solitary wasps that prey upon ground-nesting bees. We met a fast-moving velvet ant in the caldera of a sleeping Costa Rican volcano in a previous episode of Bug of the Week. The female velvet ant featured this week was discovered dashing about a local landscape. Red velvet ants are reported in most counties in Maryland and in addition to my home in Columbia, I have received images or specimens from Adamstown, Pasadena, Queenstown, and Bowie.
Velvet ants, including the one we meet today, are part of a large mimicry ring. Bright contrasting colors of dozens of species of velvet ants, including Dasymutilla occidentalis, send a warning to potential predators that an attack will be met with a potent retaliatory response, a wicked sting. The easily recognized shared appearance of so many species of velvet ants is called Müllerian mimicry, first proposed by famed German naturalist Fritz Müller. Although lacking wings, the velvet ant is no slow poke. She runs like a demon while searching for a nest of unsuspecting bumble bees. Her powerful jaws and terrible stinger probably allow her to fight her way past bumble bee defenders and enter the brood chamber of the bee hive. In the brood chamber, bumble bee larvae are nourished and cared for by bee workers. The velvet ant lays a single egg on or near the bumble bee’s babes. This egg hatches into a velvet ant larva that consumes a developing bee. When fully developed, the wasp larva forms a pupa and later emerges as an adult velvet ant. Although female velvet ants are wingless, male velvet ants have wings that are shiny and jet black. The males fly about in search of flower nectar, pollen, and mates.
It’s been a good year for bumble bees in my garden, working the blossoms and returning to nests, often abandoned chipmunk burrows. Elsewhere in the lawn, female red velvet ants prowl, searching for nests of ground nesting bees and wasps. If you see this amazing creature, avoid the urge to pick it up unless you yearn for a very memorable sting.
Wow! With a stinger like that, no wonder she is called a “cow killer”.
The lovely female velvet ant in this episode has yet another defense in addition to jaws and stinger. When grasped, she emitted a clearly audible squeaking sound. Squeaking, or stridulation in bug lingo, is a vibration produced by an insect. In this case stridulation occurs on the abdomen where one body part rubs against another. What purpose does the squeaking serve? Along with the bright red and black coloration, the loud squeak probably serves as a warning to any would-be predator that this beauty packs a punch. You see, the other common name for the red velvet ant is “cow killer.” When I grabbed one with a pair of forceps, an enormous, angry stinger emerged from the tip of her abdomen in search of something to punish. Some say that the sting of a velvet ant is strong enough to kill a cow. While this surely never happened, people stung by the velvet ant report a highly painful experience, long to be remembered.
Acknowledgements
We thank Tracy for the inspiration for this episode and for sharing an image of a beautiful eastern red velvet ant. Dr. Shrewsbury risked an awesome sting while capturing the subject for this episode. The fascinating article “North American velvet ants form one of the world’s largest known Müllerian mimicry complexes” by Joseph S. Wilson, Joshua P. Jahner, Matthew L. Forister, Erica S. Sheehan, Kevin A. Williams, and James P. Pitts, and the buzzy “Bees, wasps, and ants” by Eric Grissell were used to prepare this episode.
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