Wednesday, May 11, 2011

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.

5 comments:

  1. Interesting, so I went through my files, found a Prionyx
    http://www.flickr.com/photos/margarethebrummermann/3258545016/in/set-72157613239856374
    photo from our 2007 Mescal trip (sounds ominous, doesn't it!) and this Isodontia elegans dragging a katydid across my shoe
    http://www.flickr.com/photos/margarethebrummermann/3245904325/in/set-72157613239856374
    So they all look superficially alike. Muellerian mimicry? Their sting must hurt?

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  2. Nice images, M! I may want to borrow the Isodontia one for a blog down the road :-) I'm sure their stings would be painful, given that the venom is designed to paralyze pretty bulky prey.

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  3. Eric, hopefully you will see this. How big does Sphex lucae get? Do you happen to know anything in Genus Sphex that is really huge? I'm talking noticeably bigger than even the largest Sceliphron caementarium that I've seen. It was seen in the Bay Area of California. I never got a good photo of it, but surely there aren't that many black and red wasps over 30mm long?

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    Replies
    1. Sphex lucae doesn't get any larger than 30 mm, so I am not sure what you are describing. I suppose it could have been some kind of horntail (Siricidae), or a really large spider wasp.

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