Wasp Wednesday: Sphex lucae

Here in Tucson, Arizona, our most common member of the genus Sphex is Sphex lucae. It is also the sole North American species in the subgenus Fernaldina, named for pioneer entomologist Henry Torsey Fernald. This wasp is out and about right now, seeking nectar from “acacias” (recent changes in plant taxonomy have rendered a verdict that there are no true acacia species in North America). You would never know, however, that the male and female wasps are the same species.

A graphic difference in appearance between the genders is called “sexual dimorphism,” and many insect species demonstrate this. In the case of Sphex lucae, females are black with a red abdomen, and yellowish or violaceous wings. Males are entirely black with violaceous wings. Males also tend to be more slender-bodied than their robust mates.

Females earn their living by hunting katydids. Prey records include Insara elegans, the Elegant Bush Katydid. The wasp excavates a single-celled burrow in the soil in advance of hunting activities. She will amputate the antennae of her prey (at least sometimes), then drag her paralyzed prize back to the nest and store it there, laying a single egg on the victim. The nest entrance is then sealed and the process repeated.

Males of this species spend nights in sleeping clusters in sheltered situations such as beneath a rock overhang. Such “bachelor parties” can be intimidating to the uninitiated person, and give the impression that these are social wasps when in fact they are not.

Sphex lucae is a widespread western species, ranging from southern British Columbia to California and east to Arizona, Colorado, and Oklahoma, as well as Mexico. References also claim it occurs in the southeast U.S., but I find no recent records of this on Bugguide.net. Bugguide is not exhaustive by any means, but there are lots of photographers out there looking, too.

Watch for this wasp nectaring on many types of flowers, including White Sweetclover, Melilotus alba. You might initially mistake it for one of the Prionyx species, but note the more oval abdomen of the female S. lucae, and lack of silvery patches on the face and thorax. Happy wasp watching.