While pausing to observe a colony of industrious leafcutter ants beneath a creosote bush my attention was drawn to what first appeared to be two hairy creosote bush seed pods, one closely following the other. The pair of grayish white to tan hairy pods moved rapidly in a searching pattern that quickly led me to recognize that it was a female velvet-ant measuring approximately three-quarters of an inch in length.
Velvet-ant is the common name for wasps in the family Mutillidae and may also be known as cow-killer ants and resemble large ants. Ants and wasps are both classified in the order Hymenoptera but can be easily differentiated. Among their differences, wasps have straight antennae while the antennae of all ants are bent.
Members of the family Mutillidae demonstrate extreme dimorphism between the sexes. The females are wingless, with their thoraxes and abdomens covered in coarse hairs or setae. They also have an ovipositor that also functions as a stinger and can inflict a painful wound. Males, on the other hand, are winged, may be less hairy, and lack a stinger and are therefore harmless. Male and female velvet-ants both emit a high-pitched squeaking or chirping sound when disturbed.
The specimen observed was in the genus Dasymutilla. The generic name derives a Greek word for hairy and a Latin word for mutilated. Not a very flattering name. There are over 150 species of Dasymutilla in North America with at least three dozen found in diverse ecosystems of Arizona.
Coarse, bristly hairs cover the adult body and vary in color among the different species. Hair colors include red, orange, yellow, tan, black, gray and white. The colors warn potential predators to avoid the velvet-ant or suffer the consequences of a painful sting.
The hair colors on the adult female observed became the first clue to identifying the species observed. Species whose hairs were anything other than white to tan could be eliminated. And, the species would also have to be present in the Sonoran Desert. My first assessment was that I had observed what is commonly known as a thistle-down velvet-ant (Dasymutilla gloriosa). But no, the legs of adult female D. gloriosa are distinctly covered with white hairs. That led to the determination of Dasymutilla sackenii, which is very similar to the thistle-down velvet-ant in most aspects but has black hairless legs (Photo 1). The species is named after Baron von der Osten-Sacken, a Russian diplomat and entomologist who served as the Russian consul general in New York during the American Civil War. There are at least two common names for D. sackenii, Sacken’s velvet-ant and golden velvet-ant due to the tan to golden hairs on its abdomen.
Photo 1: Adult Dasymutilla sackenii with hairy thorax and abdomen mimicking creosote bush seed pods. Also note the black hairless legs and the straight antennae.
Adult Sacken’s velvet-ants are active from April through November. They are most active in the morning and early evening and spend the heat of the day under litter or within the canopy of creosote bushes. They feed on the plant’s floral nectar and have evolved to mimic the hairy appearance of the plant’s seed pods as camouflage from natural enemies.
Gravid female Sacken’s velvet-ants drop to the ground to search out the subterranean nests of wasps and bees. The female has a particularly hard exoskeleton which protects her from being stung by her prey as she invades their nest to lay her eggs (Photo 2). The female will use her long ovipositor to lay an egg on or near the larva or pupa of its host. Upon hatching the lava will
Photo 2: Gravid female Sacken’s velvet-ant entering a burrow in search of a ground nesting wasp or bee host colony in which to lay her eggs.
begin feeding on its immobile host; killing it within a matter of a week or two. And, once it has consumed its host the Sacken’s velvet-ant larva uses case as its own pupal chamber.
- sackenii is not listed as a threatened or endangered species. The painful sting inflicted by a female is perhaps the best reason to leave it alone.
For those interested in more information on Sacken’s velvet-ant, conduct a web search on Dasymutilla sackenii.
Note: Field observations and photographs for this article were based in full or in part from visits to the Cienega Creek Natural Preserve. A permit is required to enter the preserve. Please visit the Cienega Creek Natural Preserve web site (http://webcms.pima.gov/cms/One.aspx?pageId=1515) to learn more about the preserve and for how to obtain a permit.