Wasp Wednesday: Not What You Think

Note: Special thanks to Bob Carlson and David Wahl for reviewing these images and confirming the identification. Ichneumon wasps are a tricky lot!

It is well known that many different kinds of insects mimic stinging wasps in order to foil their own predators. This is known as Batesian Mimicry, whereby the harmless or nearly defenseless animal achieves protection by resembling a poisonous or venomous “model” animal. There is another type of mimicry known as Müllerian Mimicry in which unrelated poisonous or venomous organisms share bold patterns, typically black and yellow, black and red, black and orange, or black and white. Tarantula hawk wasps, which deliver a very painful sting, are typically colored black or metallic blue with bright orange or red wings. In southeast Arizona, there is a large ichneumon wasp, Rhynchophion flammipennis, that also sports this wardrobe.

The wasp is a member of the subfamily Ophioninae, most if not all members of which are capable of stinging themselves, using their short, sharp ovipositors in self-defense. So, it is possible that this mimicry is Müllerian rather than Batesian. Many ichneumon wasps that do not sting still mimic the stinging spider wasps (Pompilidae), thread-waisted wasps (Sphecidae), and crabronid wasps (Crabronidae).

At least one host for Rhynchophion flammipennis is the Tobacco Hornworm, Manduca sexta. The female wasp locates the host caterpillar and injects an egg into its body. The wasp larva that emerges from the egg then feeds as an internal parasite (endoparasitoid). They are “koinobionts,” meaning that they attack very young caterpillars, and draw out their own life cycle such that the host caterpillar continues to grow and mature.

The closely-related Tomato Hornworm, Manduca quinquemaculata
The wasp larva inside waits patiently, then feeds in earnest as the caterpillar nears pupation, destroying it before it actually does pupate. The wasp larva then spins a dense silken cocoon in which it pupates. Since sphinx moth caterpillars pupate underground, the wasp cocoon is likewise located in the pupal chamber in the soil.

This species is known to occur in Arizona, Mexico, Nicaragua, and Ecuador. It is a member of the tribe Enicospilini, most of which are tropical wasps. There are only two other known species in the genus. While most Ophioninae are nocturnal, Rhynchophion are day-active. They even visit flowers for nectar.

Curiously, I have found other images of this species online, but in every case the antennae are black. Perhaps antenna color varies with gender? Certainly much remains to be learned about this spectacular wasp, including whether it has other hosts. Anyone who rears sphinx moths from Arizona, Mexico, or Central America should make note of any parasitic Hymenoptera that emerge from their livestock.

The specimen imaged here was observed at the mouth of Madera Canyon in Pima County, Arizona on August 21, 2011. It hung motionless from the Desert Broom plant it was clinging to. Perhaps it collided with a vehicle entering the canyon and was recuperating.

Sources: Carlson, Robert W. 2009. “Family Ichneumonidae,” Database of Hymenoptera in America north of Mexico. Discover Life.
Gauld, Ian D. and David B. Wahl. 2013. “Subfamily Ophioninae,” Genera Ichneumonorum Nearcticae. The American Entomological Institute.
Kester, K. and J. Tuttle. 1999. “Host identified for Rhynchophion flammipennis (Hymenoptera: Ichneumonidae). Southwest. Nat. 44(1): 87-88.

Moth Monday: Palo Verde Webworm

Palo Verde trees are a fixture of the Sonoran Desert landscape in southern Arizona, so it comes as something of a surprise that so little is known about one of the most obvious insects that lives on that plant. The Palo Verde Webworm, Faculta inaequalis, remains rather mysterious despite its abundance.

This insect is a member of the family Gelechiidae (twirler moths), all of which are quite small. The adult moth varies from about 5-7 millimeters in length. Mature caterpillars are at most 12.5 millimeters.

It is the activities of the larvae that are most conspicuous. Amazingly, I can find no images of the immature stages other than these that I took myself on May 25, 2010 in Greasewood Park on the western edge of Tucson, Arizona. The caterpillars spin silken tubes along the lengths of twigs on the host tree. These silk sleeves they decorate with their droppings (frass), perhaps to increase the degree of shade they can enjoy during the heat of the day. The tubes appear to be connected to each other by a random network of additional silk threads, the “webbing” that gives these insects their common name.

The larva ventures out during cooler hours to nibble on leaves or even the bark. Palo Verde trees photosynthesize both with their leaves and their limbs; and they don’t hesitate to shed their leaves during periods of draught. Damage done by caterpillars is therefore negligible, and Faculta inaequalis seldom, if ever, becomes more than a nuisance or cosmetic pest.

The adult moths are not at all uncommon at lights at night, even in urban areas where the host trees are often planted as ornamentals. The Foothills Palo Verde, Parkinsonia microphylla, is the preferred host of this moth, and the tree is common in upland areas of the Sonoran Desert in coarse soils. Whitethorn Acacia (Acacia constricta) is an alternate, occasional host.

Part of the problem in finding out more about this peculiar lepidopteran is that it has previously been known by different scientific names, including Gelechia inaeaqualis and G. clistrodoma. Werner and Olson summarized the biology of the species in their book Insects of the Southwest, under the name Bryotropha inaequalis. Online references frequently do not use any scientific name.

The range of the Palo Verde Webworm is apparently restricted to southern California, Arizona, southern New Mexico, and Baja California Sur. Adult moths have been taken from January to April, and also August, so there are probably several generations per year.

Sources: Powell, Jerry A. and Paul A. Opler. 2009. Moths of Western North America. Berkeley: University of California Press. 369 pp.
Werner, Floyd and Carl Olson. 1994. Insects of the Southwest. Tucson, AZ: Fisher Books. 162 pp.

Spider Sunday: Flatties

Many spiders go unseen by the casual observer because they emerge only at night. Venture outside after dark, and you are likely to be astounded by arachnids you never knew existed. Take a flashlight to the outside walls of your own home and there will likely be spiders prowling across it. If you live in Florida or the southwest U.S., you will eventually see crab-like spiders of the family Selenopidae, called “flatties.”

I might not have recognized them myself were it not for Zack Lemann, Chief Entomologist at the Audubon Insectarium in New Orleans. We occasionally meet up in southern Arizona for the Invertebrates in Conservation and Education Conference at the end of July each year. In 2010, on a night field trip to Madera Canyon, Zack identified a spider sitting motionless on the outside of a restroom building as a “flattie.” I had figured it was a running crab spider in the family Philodromidae and appreciated the correction.

Flatties can be easily confused with any number of other spiders, but are readily identified by a few distinctive characteristics:

• Extremely flattened appearance. They look like they have already been the victim of someone’s shoe, so flat are they. Even the legs look cock-eyed, oriented almost completely horizontal to the body. This distinctive leg configuration is called “laterigrade,” and only a few other spider families have this feature.
• Legs increasingly longer from front to back. Note that in philodromid crab spiders like the one shown below the second pair of legs is the longest.
• Six eyes in one row. Six of the spider’s eight eyes are in one row across its face. The other two set back on either side of the face.
  
• Rear edge of sternum is notched. You have to turn the spider belly-up to see this character (good luck), but this feature of the “chest plate” is diagnostic.

Philodromid crab spider (note long 2nd pair of legs)

Their thin bodies allow flatties to slip into very narrow cracks and crevices, where they hide during the day. Most references indicate that these spiders hide under stones, or beneath bark on logs or trees, and between the bases of leaves of dense plants. I have personally never discovered them on the ground or under objects. They have always appeared on vertical surfaces at night in my experience.

These are medium-sized spiders, adults measuring from 7.5-13 millimeters in body length. Their sprawling legspan makes them appear larger. The mottled gray or brown or yellowish coloring helps to camouflage them on rock surfaces and tree trunks. They likely wait in ambush for prey, though when disturbed they can sprint with startling speed.

There are five species found north of Mexico, all in the genus Selenops. They collectively range from southern California to western Texas, and also in Florida and the Caribbean islands.

Sources: Jackman, John A. 1997. A Field Guide to Spiders & Scorpions of Texas. Houston: Gulf Publishing Company. 201 pp.
Kaston, B.J. 1978. How to Know the Spiders (3rd Ed.). Dubuque, IA: Wm. C. Brown Company Publishers. 272 pp.
Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds). 2005. Spiders of North America: an identification manual. American Arachnological Society. 377 pp.

Fly Day Friday: Three-banded Robber Fly

Too often the first thing that pops into people’s minds when they hear the word “fly” is a house fly or a horse fly, or some other nuisance or pest fly. I think if the popular association were with robber flies, family Asilidae, public opinion of the Diptera would be vastly improved. Case in point is the little Three-banded Robber Fly, Stichopogon trifasciatus.

Far from being pests, or even pesky, robber flies are assassins of other insects, including the ones that bite and sting us. Many species are quite large, but the Three-banded Robber Fly is rather diminutive, measuring only 10-15 millimeters (and the top end of that spectrum might be generous).

Stichopogon trifasciatus is one of ten North American species in the genus Stichopogon, but the most widespread and easily recognized. It ranges from southern Canada to Central America, and coast to coast in North America. The bright silvery or blue-gray of the body, and distinct broad bands on the abdomen help set this fly apart from similar asilids. There is enough variation, however, to be somewhat confusing. The former species S. salinus, collected along the western edge of the Rockies from Idaho to northern Arizona, was recently synonymized with S. trifasciatus (Barnes, 2010).

The habitat and behavior of the Three-banded Robber Fly is suggestive of many tiger beetles. These flies like the beach! Well, rocky or gravelly beaches anyway. I have encountered them most frequently along the rocky edges of rivers and streams, but also well away from water. I found one in Colorado Springs on a rugged unpaved road. They like to be close to the ground, but on an elevated perch if possible. Startle one and, like a tiger beetle, it will take flight for a short distance before alighting again.

The adult flies feed mostly on other small flies, which according to one study amounted to 85% of their diet (true bugs, order Hemiptera, accounted for another 10%). Still, another observer noted that this species preys on small spiders to a large degree (Bromley, 1934). The fly attacks prey that is crawling on the ground, rather than intercepting it in flight as other species are known to do.

The life history of S trifasciatus remains mostly mysterious, but courtship behavior has been observed. The male apparently hovers back and forth before the female, his legs hanging and waving. He then attempts to copulate by pouncing on her (Preston-Mafham, 1993). Doesn’t sound like a romantic day at the beach, but….

Sources: Barnes, Jeffrey K. 2013. “The Genus Stichopogon Loew (Diptera: Asilidae) in America North of Mexico,” Proc. Entomol. Soc. Wash. 115(1): 9-36.
Barnes, Jeffrey K. 2010. “Revision of Nearctic Stichopogon Species (Diptera: Asilidae) With White-banded Abdomens, Including Description of Stichopogon venturiensis, New Species, From Coastal California,” Proc. Entomol. Soc. Wash. 112(3): 367-380.
Bromley, S.W. 1934. “The Robber Flies of Texas (Diptera: Asilidae),” Annals Entomol. Soc. Am. 27: 74-113.
Hull, Frank M. 1962. Robber Flies of the World. Washington, DC: Smithsonian Institution Bulletin 224, Parts 1 and 2. 907 pp.
Preston-Mafham, Rod and Ken. 1993. The Encyclopedia of Land Invertebrate Behaviour. Cambridge, Massachusetts: The MIT Press. 320 pp.
Raney, Herschel. 2003. “Stichopogon Page,” Random Natural Acts