Fly Day Friday: Comantella robber flies

Here along the Front Range in eastern Colorado, among the first flies of spring are unique little robber flies in the genus Comantella. When I first saw one I thought it looked like a march fly (Bibionidae), but behaved like an asilid.

Comantella are also among the last flies seen in the fall, as demonstrated by the above image taken on Novermber 29, 2011 in Colorado Springs. This unusual seasonal appearance of the adults (early and late), plus the presence of a slender spur on the tip of the front tibia (“shin” segment), helps to separate this genus from similar genera in the Asilidae. They are decidedly humpbacked when viewed in profile. Little appears to be known concerning their biology, though it is suspected that the adult flies overwinter in protected places. One specimen of the species C. fallei was observed preying on a small wolf spider in the genus Pardosa (Dennis, et al., 2012).

The taxonomy of Comantella is not very straightforward, either. At least one expert on asilids believes the genus is in bad need of revision. Current keys to species seem to revolve around the length of the terminal style as compared to the third antennal segment, and coloration of the hairs on the body.

These are small or medium-sized flies, 10-15 mm in length, and covered in long hair, even on their legs. The top of the thorax features a “mane” that can best be described as a Mohawk hairstyle.

There are only four currently-recognized species of Comantella. C. pacifica is found from British Columbia south to Nevada and Utah. C. cristata is known from Idaho and California. C. rotgeri occurs in Colorado, New Mexico, and Alberta. C. fallei ranges in California and Colorado.

I expect to see more of these flies any day now. Last year I found this mating pair on March 12, but the winter was very warm. In all instances I have found Comantella perched on the ground (rarely on vegetation), usually on bare soil, in vast open fields.

Sources: Cannings, Robert A. 2012. “A Checklist of the Robber Flies (Diptera: Asilidae) of British Columbia,” University of British Columbia.
Cole, Frank R. 1969. The Flies of Western North America. Berkeley: University of California Press. 693 pp.
Dennis, D. Steve, Robert J. Lavigne, and Jeanne G. Dennis. 2012. “Spiders (Araneae) as Prey of Robber Flies (Diptera: Asilidae),” J. Entomol. Res. Soc. 14(1): 65-76.
Dennis, D. Steve, Jeffrey K. Barnes, and Lloyd Knutson. 2008. “Pupal cases of Nearctic robber flies (Diptera: Asilidae),” Zootaxa 1868. Auckland, New Zealand: Magnolia Press. 98 pp.

Hull, Frank M. 1962. Robber Flies of the World. Washington, DC: Smithsonian Institution Bulletin 224. 907 pp. (2 vols.).
James, Maurice T. 1941. “The Robber Flies of Colorado (Diptera, Asilidae),” J. Kans. Entomol. Soc. 14(1): 27-53.
Lavigne, R.J., William F. Barr, and G.M. Stephens. “Checklist of the Asilidae of Idaho,” College of Idaho. 26 pp.
Neslon, C. Riley. 1987. “Robber Flies of Utah (Diptera: Asilidae),” Great Basin Nat. 47(1): 38-90.

Moth Monday: Sophora Worm

One of the challenges I enjoy is matching caterpillars to their adult moths, and vice versa. Usually one of the two is spectacular and obvious, and the other is cryptic and/or scarce. Such was the case when I encountered the larvae known as the Sophora Worm, Uresiphita reversalis, of the family Crambidae.

I found many of the caterpillars amid their silken webbing on a common ornamental shrub in Tucson, Arizona on May 20, 2010. Turns out the plant was Texas Mountain Laurel, Sophora secundiflora, easily identified by its large, purple flowers and resulting robust pea-like pods. This is a native host for the moth, but the caterpillars are also known to eat non-native “broom” plants such as French Broom (Genista monspessulana), and other Genista species. This habit has given rise to an alternate name for the Sophora Worm: “Genista Broom Moth.”

Additional host plants include lupines (Lupinus), acacia (Acacia), false indigo (Baptisia), and other leguminous plants. It is also reported from Crapemyrtle (Lagerstroemia indica) and honeysuckle (Lonicera), but these are probably incidental.

The caterpillars feed out in the open, in groups, and during the day, in stark contrast to most caterpillars that are solitary and nocturnal, the better to avoid potential predators. The bold colors suggest that Uresiphita reversalis is distasteful to their enemies, and indeed they accumulate the toxins of their host plants for use in their own self-defense. They sequester the quinolizidine alkaloids found in their leguminous host plants, incorporating the chemicals into their exoskeleton. Even so, damsel bugs and other predatory insects with piercing-sucking mouthparts simply bypass this external defense by puncturing the cuticle and feeding on the internal tissues of the caterpillars (Bernays and Montllor, 1989).

The length of the life cycle of this species varies considerably depending on season and latitude. It can be as short as five weeks from egg to adult under optimal summer conditions in southern climes, and as long as 25 weeks in winter in the more northerly reaches of its range. There may be four or five generations annually. In Berkeley, California there are two major flight periods, one from March to May and the other from July to October. Overwintering usually occurs in the pupal stage, but adults are sometimes found during this season as well.

Eggs are laid in clusters (averaging about 19 per clutch in the lab) on the upper- or underside of leaves. The larvae go through five instars (an instar is the interval between molts). Pupation occurs inside an opaque, white cocoon woven amid dense webbing.

The adult moth has a wingspan of 27-34 millimeters. They are seen most often during the day and are easily startled from their resting place. The body and legs of the moth are bright white. The hind wings, usually not visible when the insect is at rest, are bright yellow or orange.

One reference asserts that the Sophora Worm is native to Mexico and the southwest U.S. and has spread with its hosts up the coast of California to the Bay area; and also north and east to the Great Lakes and mid-Atlantic states, even Maine and Nova Scotia. It became established in Los Angeles in 1930, spreading rapidly from there. By the 1980s it was spreading through the San Joaquin and Sacramento Valleys (Powell and Opler, 2009).

I didn’t find an adult moth until more than a year later. The specimen imaged here was in the same neighborhood where I found the caterpillars, on June 11, 2011.

Note that this moth was formerly classified in the family Pyralidae, and is often still placed there incorrectly on several internet resources. It is currently in the family Crambidae, subfamily Pyraustinae.

Sources: Bernays, E.A. and C.B. Montllor. 1989. “Aposematism of Uresiphita reversalis Larvae (Pyralidae),” J. Lep. Soc. 43(4): 261-273.
Leen, Rosemary. 1995. “Biology of Uresiphita reversalis (Guenée) and Comparison With U. polygonalis maorialis (Felder) (Crambidae),” J. Lep. Soc. 49(2): 163-170.
Powell, Jerry A. and Paul A. Opler. 2009. Moths of Western North America. Berkeley: University of California Press. 369 pp.

Spider Sunday: Hololena Funnel-web weavers

Sometimes you go looking for spiders, and sometimes it seems they come looking for you. The second statement isn’t really true of course, but at the least you usually don’t have to go far to find arachnids. Here in the western United States, funnel-web weavers in the genus Hololena are abundant, even in the average yard or garden. Entire hedges can be full of their sheet-like webs.

Meanwhile, juvenile specimens, and mature males, will wander away from their webs, often straying indoors. It can be startling to suddenly have a spider appear on the wall while you are watching television.

Hololena is easily confused with other genera in the family Agelenidae, and to be fair it is only microscopic examination of certain body parts that can confirm the identity of any given specimen. Hololena is, however, readily separated from Agelenopsis based on the length of the spinnerets. Agelenopsis (and Calilena, too) have long spinnerets usually held parallel to each other. Hololena has short spinnerets, often directed somewhat inward toward each other.

These are medium-sized spiders, mature females ranging from 9-12 millimeters in body length, males 8-9 millimeters. Agelenopsis average substantially larger, about 10-20 millimeters. Most funnel-web weavers share a similar color pattern: two parallel or converging dark stripes on a pale carapace; a central reddish or brownish band running the length of the abdomen, often bordered by pale, wavy lines. The legs are often annulated (alternating bands of light and dark).

The genus Hololena appears to be restricted to the western third of the U.S., from Washington and Idaho south to southern California and New Mexico. There are approximately thirty recognized species, but the genus is in dire need of revision according to some arachnologists.

Agelenids in general spin thick, flat, hammock- or bowl-shaped webs with a funnel-like retreat in one corner. The web is not sticky. A tangle of threads above the silken platform intercepts flying insects, knocking them onto the sheet. The spider is extremely sensitive to vibrations and dashes out immediately to subdue its prey. It quickly drags the victim back into its lair to feed.

Male spiders have to approach females cautiously and deliberately. In Hololena, the male more or less bounces his legs and abdomen on the female’s web, creating a bout of one to six vibrations. A receptive female responds by drawing in her legs and lapsing into “cataleptic paralysis.” The male will draw closer and repeat his vibrational overtures until he is accepted or repelled. He then crawls over her back, gently grasping her two hind legs and dragging her deeper into her retreat.

Mating occurs when the male is able to turn the female on her side and insert one of his palps into her genital opening (epigynum). He repeatedly inserts his palp and pumps sperm into her before attempting to maneuver her into a position where he can insert the opposing palp. The female usually offers no resistance during this process. Once finished, the male grooms his palps and walks off the web. Occasionally his mate recovers from her paralysis prematurely and actively chases him off her web.

Mature males can be seen looking for females deep into the fall. The specimen shown above was observed on October 29, 2012 in Colorado Springs.

Researching this post I was startled to learn that there are confirmed cases of Hololena spiders biting people. It should be noted that actual spider bites are a pretty rare phenomenon, and the usual result is mild pain and swelling that doesn’t require medical treatment. Dr. Richard Vetter at the University of California, Riverside, published a note documenting three separate, verifiable instances of adult people who were bitten by Hololena spiders. Two were adult men, bitten by female spiders. The victims experienced headaches and four-hour episodes of vomiting. The third victim was an adult woman, bitten by a male spider, who experienced a very mild reaction. All three were perfectly fine in a matter of days without seeking medical attention (Vetter, 2012).

One need not be fearful of these spiders. I prefer to be enchanted by their delicate yet durable spinning work. I remember vividly a light snowfall we had here in Colorado Springs on October 25, 2012. The only place the flakes persisted was on Hololena spider webs. What an amazing scene! Take a look around your own neighborhood, especially on damp early mornings when dew has condensed. You will be amazed by the number of webs you hadn’t known were there.

Sources: Fraser, Jack B. 1987. “Courtship and copulatory behavior of the funnel-web spider, Hololena adnexa (Araneae, Agelenidae),” J. Arachnol. 15: 257-262.Vetter, R.S. 2012. “Envenomation by Spiders of the Genus Hololena (Araneae: Agelenidae),” Toxicon 60(3): 312-4.

OrThoptera Thursday: California Angle-wing Katydid

In previous weeks I have written about the Greater Angle-wing Katydid and the Lesser Angle-wing Katydid, but there are four other species in the U.S. One of these, Microcentrum californicum, is found commonly in Arizona, and the length of California west of the Sierras.

The California Angle-wing Katydid is the smallest member of its genus, adults ranging from 41-52 millimeters. Note that the male has a brown stridulation area (its “shoulders”) like the Lesser Angle-wing, but its geographic range leaves no room for confusion.

The specimen shown here was attracted to a blacklight set up in Peppersauce Canyon in the Catalina Mountains of Pima County, Arizona on September 2, 2011. There was also a female Greater Angle-wing found in the same location on the same night.

The remaining Microcentrum species include M. louisianum, the Louisiania Angle-wing, found from Louisiana and Mississippi north through parts of Arkansas and Tennessee to the bootheel of Missouri. Microcentrum minus, the Texas Angle-wing, is found only in extreme south Texas; and the Southwestern Angle-wing, M. latifrons, is recorded from the Big Bend area of Texas and the southeast corner of Arizona.

>Sources: Capinera, John L., Ralph D. Scott, and Thomas J. Walker. 2004. Field Guide to Grasshoppers, Katydids, and Crickets of the United States. Ithaca: Comstock Publishing Associates (Cornell University Press). 249 pp.
Eades, David C., Daniel Otte, Maria Marta Cigliano, and Holger Braun. 2013. Orthoptera Species File Online. Version 5.0/5.0
Walker, Thomas J. and Thomas E. Moore. 2013. Singing Insects of North America. University of Florida.