Wednesday, March 21, 2012

Wasp Wednesday: Liris

Last “Wasp Wednesday” I featured some very early emerging ”Winter Wasps” that I have recently encountered during the unseasonably warm weather here in Colorado Springs. Today I’ll focus on one of those: Liris. They are among the first solitary wasps of the family Crabronidae that you are likely to see in the spring. That is because the females overwinter as adults.

Beyond the early appearance of these wasps, I find other characters at least semi-reliable for distinguishing Liris from other members of the tribe Larrini. The antennae, frequently held parallel and straight out from the head, are proportionately longer in Liris than in Tachytes and Tachysphex. Tachysphex is usually considerably smaller than Liris, often with the abdomen entirely red, or red in part, and terminating in a very pointed pygidium. Tachytes frequently has bright green eyes, and is generally stockier in appearance than Liris. Tachytes rarely sit still for more than a millisecond (or so it seems), whereas Liris seems to move at least slightly more slowly.

Liris is a large genus with most of its diversity in the tropics. Over 260 species are known worldwide, but that is likely to increase substantially since the genus is poorly known in the New World tropics and in Asia. Krombein and Gingras revised the North American species (including Mexico) in 1984, but only two species, L. argentatus and L. beata are consistently found north of the extreme southern U.S. Species identification hinges on obscure characters like the male genitalia, female pygidium (a triangular plate on the last dorsal abdominal segment), and the size and shape of the sensory areas on the antennal segments. When the reference includes electron microscopy images, you can forget about making species identifications in the field.


illustration by Judy Jay (Bohart & Menke, 1976)

Still, I am willing to bet that the species I am observing here in Colorado Springs is Liris argentatus. It is by far the most abundant of all North American species in the genus, and found from southern Ontario and Massachusetts west to southeast Washington state, south to Panama. It is also one of the most studied species, so there is a wealth of information on its biology and behavior.

Females of L. argentatus vary from 9.5-15.4 mm in body length. Males are 6.4-10.7 mm. They are thus medium-sized insects. Both genders are black, but covered in fine, short, reflective hairs that give them a decidedly silvery appearance in bright sunlight.

My observations over the last two weeks indicate that one of the first priorities of newly-emerged females is to find water. Indeed, I have seen at least three individuals, on two separate occasions, taking water from damp soil in otherwise dry arroyos in Red Rock Canyon Open Space and Garden of the Gods, right around noon or one o’clock PM.

Both sexes will also seek fuel in the form of honeydew secreted by scale insects, and nectar from flowers as diverse as thistle, sunflower, wild carrot, and goldenrod.

The females next prepare nest burrows. Lacking a strong rake of tarsal spines on their front legs, females of L. argentatus may clean out pre-existing tunnels and cavities to use as nests. There are still plenty of records of this wasp digging its own burrows, terminating in one to three underground cells (one recorded nest had a cluster of ten cells). The nest varies from 10-14 centimeters in depth and is left open while the wasp begins its search for prey.

Crickets in the family Gryllidae are the host animals sought by these wasps. Both adult crickets and nymphs are taken. The prey is paralyzed by the wasp’s sting, facilitating easier transport of what is truly a bulky animal. The wasp grasps the prey by the base of its antennae and lugs it overland on most occasions. One to four (sometimes more) crickets are placed in each cell at the bottom of the burrow, an egg laid on the last victim. Oddly, the crickets are not completely paralyzed, recovering the ability to walk weakly, or even jump in some cases.

Once a nest is filled, the wasp fills the tunnel loosely with a combination of soil particles and fragments of dry vegetation, small pebbles, and other debris. She hides the entrance by kicking sand or soil over it, then leaves to repeat the whole scenario again.

Nests constructed in spring are remarkably devoid of parasites, but then the “satellite flies” that plague so many solitary wasps have not yet emerged themselves. Even velvet ants are only just beginning to stir. Nests made in the summer do suffer parasitism.

Those late-season wasps that do make it will mate before winter. Only the females live through the cold months, evidently inside burrows they dig for the purpose of hibernation.

Those of you in the U.S. and Canada can probably find these wasps in your own area very soon, if not right now. Please feel free to share your comments and observations here. There is still so much to learn about even the most common of insects, and you could be the one to make a significant contribution to our collective body of knowledge.

Sources: Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World: A Generic Revision. Berkeley: University of California Press. 695 pp.
Krombein, Karl V. and Sandra Shanks Gingras. 1984. “Revision of North American Liris Fabricius (Hymenoptera: Sphecoidea: Larridae),” Smithson. Contrib. Zool. No. 404. 96 pp.
Kurczewski, Frank E. and Margery G. Spofford. 1987. “Further Observations on the Nesting Behavior of Liris argentatus (Hymenoptera: Sphecidae),” Gt. Lakes Entomol. 20(3): 121-125.
O’Brien, Mark F. and Frank E. Kurczewski. 1981. “Nesting and Overwintering Behavior of Liris argentata (Hymenoptera: Larridae),” J. Georgia Entomol. Soc. 17(1): 60-68.

1 comment:

  1. I just found the first one of this group in our backyard, but it's suspended in id guess work in BugGuide, because J. Asher thinks the ocelli are too normal for Tachysphex but it really looks like one. http://bugguide.net/node/view/622438.

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