Wasp Wednesday: Evaniidae

It is always a challenge to select a wasp to profile on “Wasp Wednesday,” in part because there are so many to choose from, but also because I don’t have that many images of wasps…yet. I was thrilled today (August 31, 2010) to find an unusual and wonderful wasp to profile, right at my workplace at the Tucson Botanical Gardens. Right there inside the tropical greenhouse were flitting little ensign wasps.

Ensign wasps of the family Evaniidae get their common name from the tiny, flag-like abdomen that they habitually “wave” as they walk. They have a start-and-stop gait, bobbing their abdomens as they go.

Globally, evaniids are represented by 20 genera and 435 species. There are eleven species in the family Evaniidae in North America north of Mexico, in four genera. Two of those species are not native, and one of those immigrants is the one in the greenhouse at the Tucson Botanical Gardens: Evania appendigaster. It is large for an evaniid, adults measuring up to eleven millimeters in body length. Perhaps the most striking feature of the insect is its bright turquoise compound eyes, at least in living specimens.

Evania appendigaster may be native to Asia, but is widespread in tropical and subtropical regions. Here in the U.S. it is exclusively associated with urban areas, and mostly inside buildings. There is good reason for this strange habitat. This species is a parasite of the egg capsules of cockroaches. Its hosts include the American Cockroach, Periplaneta Americana, Australian Cockroach, P. australasiae, and Oriental Cockroach, Blatta orientalis. Those roaches are also aliens to North America, probably having crossed the Atlantic Ocean on slave ships from Africa.

The first U.S. record of Evania appendigaster (it has no common English name, sorry) was probably on June 5, 1879, from Washington, DC, as represented by a specimen in the collection of the Smithsonian Institution. Today, this species is most common along the Atlantic Seaboard and the Gulf Coast, as well as here in Arizona.

What is the life cycle of this wasp? Females search for the egg capsules (oothecae) of the roaches. Once it locates a capsule, the female wasp inserts her ovipositor into one of the eggs in the package and lays her own egg. She then departs in search of another ootheca. Her egg eventually hatches inside the roach capsule and the larva that emerges then consumes the cockroach eggs. It eventually pupates and the adult wasp chews its way out of the roach ootheca a week or so later.

I have observed the adult wasps feeding on honeydew secreted by aphids, like here on a cottonwood leaf in the Sweetwater Wetlands in northwest Tucson. Indoors, perhaps they will feed on spilled beverages? Who knows?

Excellent images and phylogenetic information can be found at the Tree of Life Web Project, courtesy of Andrew R. Deans. Deans is also the driving force behind another internet project, ”Evanoidea Online”. This resource covers not just the Evaniidae, but also related families of equally interesting wasps. There are also “keys” at that website that allow you to identify the North American Evanoidea.

Ensign wasps are not commercially available for cockroach control, at least to my knowledge, but it might be a venture worth considering. I know that I would sooner employ a non-toxic, mobile pest-control device to eradicate roaches instead of reaching for some kind of chemical at the local hardware store. The wasps are far more engaging, too.

Sources: Smith, David R. 1998. "Evaniidae in the Mid-Atlantic States: Seasonal Occurrence and Identification," Proc. Entomol. Soc. Wash., 100(2): 275-285.

Flickr Photostream

I admit I might be cheating a little, but today I am re-directing you to my Flickr Photostream for some eye candy. Each of the new images there includes a little bit of information about the creature depicted, and/or the circumstances under which it was imaged. Hope you enjoy. I'll be back soon with additional posts.

Wasp Wednesday: Dryudella

On the morning of May 8, 2010, I was looking for insects in my immediate neighborhood in midtown Tucson, Arizona. The weather was partly cloudy, and relatively warm as I recall. Walking up a residential street, something hanging from the stem of a Desert Marigold flower caught my eye. Much to my surprise it was a female wasp in the genus Dryudella, and she had prey.

Up until this point I had never seen a female in this genus of wasps, members of the family Crabronidae. I had only collected less than half a dozen males in thirty some years. They are not large, and this female was probably less than ten millimeters.

Solitary by nature, the ten North American species in the genus belong to the subfamily Astatinae, collectively known to prey on “true bugs” in the order Hemiptera. Little more is known of their biology. Females are fossorial, meaning that they dig nest burrows in the soil. Our species in the U.S. and Canada are almost completely restricted to the western portions of the continent where they frequent arid habitats.

Males differ graphically from females when it comes to their eyes. The eyes of male Dryudella are holoptic, meaning they wrap around the face and meet at the top of the head. They use that extraordinary field of vision to detect females and rival males from perches at the tips of twigs and branches of shrubs and weeds. Their hind wings are also much broader than those of the females, and they are able to fly amazingly fast. Watch one and it will dart at warp speed from its perch, in pursuit of some target, only to return just as quickly, as if it had perfected time travel.

The female I found was apparently resting, and who could blame her. Here she was lugging a paralyzed scentless plant bug (genus Harmostes) which she carried beneath her. She wobbled.

She wavered.

She finally flew off, but not before I got a nice series of images of her. I am not certain whether this documents a new host (prey) record or not. Dryudella is not as specialized in its prey selection as other genera in the Astatinae subfamily. Recorded prey includes assassin bugs, negro bugs, stink bugs, shield bugs, seed bugs, burrower bugs, broad-headed bugs, and scentless plant bugs. Both adults and nymphs may be used as provisions for the offspring of the female wasp.

Blue-eyed wasps. Who woulda thunk it? Being observant has its rewards, and carrying a camera helps preserve those moments as well as provide evidence of behaviors and ecological relationships that might not yet be known. I’m hoping this particular wasp was successful in raising another generation. She sure was working hard….

Sources:
Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World. Berkeley: Universithy of California Press. 695 pp.
Krombein, Karl V. et al. 1979. Catalog of Hymenoptera in America North of Mexico. Washington, DC: Smithsonian Institution Press. Vol. 2, pp 1199-2209.

Wasp Wednesday: Chlorion aerarium

I think the first time I saw specimens of the Steel Blue Cricket Hunter, Chlorion aerarium, was in the collection at Oregon State University in about 1979. I remember being somewhat surprised that the species even occurred in that state, but here it was, all impressive in metallic teal. The specimens dated back at least a couple of decades or so, but I hoped I could eventually find specimens myself.

This magnificent wasp is frequently confused with the Blue Mud Dauber which I wrote about last week. Both are in the family Sphecidae, and indeed they can sometimes be difficult to tell apart in the field, especially the males. Chlorion aerarium is generally a significantly larger wasp, much brighter in color (though a deep metallic violet blue in much of eastern North America), and less hairy than the Blue Mud Dauber. The antennae of Chlorion originate lower on the face, and the mandible has a single tooth (the mandible of Chalybion is simple). Obviously, one can’t easily examine live specimens at close range to note those more subtle characters. Not without getting painfully stung, anyway.

The Steel Blue Cricket Hunter is so named because the solitary females hunt crickets of the family Gryllidae as prey. Watch for the females scouring the ground and peering into nooks and crannies in search of crickets. Once she locates one, she stings it into weak paralysis and flies it or carries it to a simple burrow she excavated previously. She sometimes chooses to dig her own burrow from inside the entrance of a cicada killer burrow, oddly enough.

The burrow may terminate in more than one cell (multicellular burrows may even be the norm). The female places several crickets in each cell, closing the cell with a plug of soil between forays. A single egg is laid on one of the victims. The larva that hatches then consumes the cache of crickets.

Both genders fuel their frenetic activity mostly on fermenting plant sap oozing from wounded shrubs. That is certainly the case here in Arizona where they can congregate by the dozens on oozing Desert Broom plants (Baccharis sarothroides). All of my images here are from such circumstances. Only rarely does this wasp visit flowers for nectar.

While I have found this species to be common and widespread over most of the United States and adjacent southern Canada, I still remember well my first encounters with them back in The Dalles, Oregon, in the Columbia River Gorge. I actually took a Greyhound bus from Portland to explore the sandy high desert habitat there and found many species of wasps. A railroad bed ran near the river, among tall grasses, mountain ash trees, and an overabundance of poison oak. It was in this area that I found many male Chlorion flitting among the poison oak.

Emerging from the tall grass at the very edge of the railroad tracks I saw a female on the ground. She shined like a living jewel, her body in vivid metallic blue with shimmering blue and violet wings that flicked nervously as she searched for prey.

The following autumn at Oregon State I took my specimens to my mentor, the late Dr. George Ferguson, eagerly awaiting his expert opinion. He initially concluded they were merely Blue Mud Daubers. I confessed I was disappointed, having thought they were Chlorion. Dr. Ferguson then put one under his microscope and said “By golly, you’re right! They’re awful small, though.” What music to my ears to be validated by someone I greatly admire to this day.

Common as a given insect might be, there is still a thrill in discovering it for oneself, and if this blog accomplishes nothing else than to nudge a reader into the field in search of his or her own Moby Dick, then I cannot ask for more. Go, find the “bug” of your own dreams, and tell everyone else about it, too.