Wasp Wednesday: Trypoxylon

Last week I reported on the “Keyhole Wasp,” Pachodynerus nasidens, but mentioned that there are other kinds of wasps that also go by that common name. Meet the members of the genus Trypoxylon in the family Crabronidae. Most species of these spider-hunting wasps nest in pre-existing cavities, such as old nail holes. They are common, but usually go unnoticed by the casual naturalist.

Trypoxylon wasps can be separated from other wasps by a couple of distinctive characters. The abdomen is long, slender, and clavate (club-shaped, the tip of the abdomen being decidedly blunt). There is only one submarginal cell in the forewing. Lastly, the compound eyes are emarginate, meaning they are obviously “notched” in the middle, on the inner margin.

The genus is divided into two subgenera, the small species in the subgenus Trypoxylon, while medium-sized and large species are in the subgenus Trypargilum. Both groups are collectively distributed over most of the North American continent. The only ones I have managed to image in the wild so far are species of Trypargilum. Despite their larger size, they defy identification to species without collection of actual specimens. However, their shared life cycles are similar enough to generalize.

Adult females are solitary, and seek natural cavities in which to nest. This typically means hollow twigs, old beetle borings in dead, standing trees, vacated insect galls, and abandoned nests of mud dauber wasps. Those natural tunnels are progressively partitioned into individual cells along their length as the wasp first provisions the deepest one, then moves forward toward the entrance.

Interestingly, the males often participate in nest maintenance, at the least by actively guarding the nest entrance while the female is away hunting prey or harvesting mud for one of the partitions. This is extremely valuable because the nest is besieged by parasitic insects that would find easy pickings were it not for the male wasp’s devotion to duty. Males do not sting, but they physically block entry of parasites and behave aggressively toward those enemies. Observers have also noted that in some species of Trypoxylon the males may take prey brought in by the female and place it in the cell while she resumes hunting. Males can also assist in cleaning out the cavity before nesting begins, and aiding in the building of partitions and the mud plug closing the finished nest. Naturalist Phil Rau called those species demonstrating couples teamwork “Patriarchate wasps.”

The two species found commonly here in Tucson, T. californicum and T. clavatum clavatum, average from 1-5 cells per nest. Spiders are the prey of these wasps, and mostly immature spiders at that. Some species hunt mostly web-building spiders, while other species seek free-ranging spiders, but there always seems to be at least a slight degree of overlap in prey selection. Jumping spiders, crab spiders, running spiders, lynx spiders, and sac spiders are recorded prey for T. californicum. The same general prey base applies to T. c. clavatum, but also add small wolf spiders and a good selection of orb weavers. Anywhere from 5-20 spiders are stocked in each cell, sometimes more, occasionally less (3 is the recorded minimum, 36 the maximum).

One egg is laid in each cell, and the larva that hatches consumes the cache of paralyzed arachnids. When mature, the larvae spins a cocoon. Apparently, the composition and architecture of the cocoon is species-specific, with varying amounts of silk, saliva, and soil going into the matrix. Inside the cocoon the larva pupates, and an adult wasp eventually emerges.

I would be remiss if I failed to mention that there is one species in North America that breaks all the rules. That would be the “Pipe Organ Mud Dauber,” Trypoxylon politum. This is a very large wasp for the genus, glossy black with white “ankles” on the hind legs, and it constructs large, linear mud nests that resemble the pipes on an old-fashioned organ. This wasp ranges over most of the U.S. east of the Great Plains. You can learn more about it in this excellent archived entry from ”This Week at Hilton Pond” and at Bugguide.net.

You can create habitat for the cavity-nesters by simply drilling holes in a block of wood and hanging it up under an eave on your home, shed, or barn. One pair of researchers here in Tucson used a ¼ inch bit drilled to a depth of 77 millimeters, and a 3/16th inch bit drilled to 124 millimeters, with good success. A good primer on how to build such “trap nests” can be found here. Give it a try!

Sources: Matthews, R.W. and J.R. 1968. “A note on Trypargilum arizonense in trap nests from Arizona, with a review of prey preferences and cocoon structure in the genus.” Psyche 75: 285-293 (available online as a PDF. T. arizonense is an outdated name for T. californicum).
Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.

Moth Flies

It’s a moth! It’s a fly! It’s….a “moth fly!” So goes the confusion upon encountering one of the most common yet confounding dipterans. Moth flies belong to the family Psychodidae in the order Diptera. Most people have seen these diminutive, fuzzy creatures in the bathroom, perched on the side of the sink basin, or on a nearby wall. Where do they come from? Are they harmful?

The answer to the second question is easier than the first. Moth flies are not harmful, at least in the sense of public health. They do not bite, unlike their cousins the sand flies, also in the family Psychodidae, but members of a different subfamily. Sand flies not only bite, but are vectors of leishmaniasis, a parasitic disease occurring mostly in the tropics. Moth flies are mostly a nuisance, though they can reach high population densities around sewage treatment plants.

Adult moth flies are active mostly in the evening hours, and are attracted to lights after dark. Consequently, they may easily enter the home through an open door or window. While they can breed indoors (more on that later), they normally seek wet, decaying organic matter where the female can lay from 30-200 eggs in a loose cluster. Typical sites that attract them include clogged rain gutters, compost heaps, birdbaths, sewer drains, septic tanks, and filter beds at sewage treatment facilities.

I find it amusing that the scientific name of one of the most common species of moth flies, the “Filter Fly,” is Clogmia albipunctata. They certainly don’t cause clogged drains. In fact, they may be better at preventing clogs than a bottle of Draino or Liquid Plumber. This common household species can carry out its life cycle inside the pipes under your sink or shower, no matter how clean your bathroom is.

The eggs hatch between 32 and 48 hours after the female lays them, the larvae proceeding to feed on algae, fungi, microbes, and other organic matter in the gelatinous film of goo lining the average sink drain. I suspect that the many questions I receive about “worms” in the sink or shower refer to mature larvae of Clogmia that are seeking a place to pupate, or that are flushed from their normal feeding niche. It takes a larva from nine to fifteen days to reach the point where they are ready to graduate to the pupal stage. The pupa usually resides on the surface of the same organic film as the larva inhabits. An adult fly emerges from the pupa in an astounding 20-40 hours.

Moth fly larvae are actually considered beneficial organisms in the treatment of municipal sewage, so bear that in mind the next time you encounter one. You have to admire them just a little bit for capitalizing on the artificial habitats we have inadvertently created for them.

Sources: For way better images of adults and larvae, take a look at this remarkable life cycle series shot by my good friend Ashley Bradford. She is definitely not the squeamish sort! Also check out this fantastic fact sheet produced by the Connecticut Agricultural Experiment Station. It gives more detailed information than I have room for here, including how to prevent infestations and deal with existing ones.

Wasp Wednesday: Pachodynerus

Last week I introduced you to a social wasp called the ”Mexican Honey Wasp” in the family Vespidae, subfamily Polistinae. That species appears to be the model for a mimicry ring involving several unrelated solitary wasps, and a type of soldier fly….and those are only the ones I personally know about.

One of the best of these mimics is Pachodynerus nasidens, a mason wasp in the family Vespidae, subfamily Eumeninae. It goes by the common name “Keyhole Wasp,” but I have heard that epithet applied to other wasps as well, so will stick with the Latin here.

The markings of this wasp are essentially identical to those of the Mexican Honey Wasp, and a cursory look is not enough to distinguish the two. Oddly, Pachodynerus nasidens has at least a slightly broader range than Brachygastra mellifica, occurring in southern Arizona, Brownsville, Texas, and Plantation Key in Florida, as well as throughout Mexico, Central America, and the Antilles. Interestingly, it has been “exported” accidentally to Hawaii and Micronesia. The U.S. range strongly suggests that the Mexican Honey Wasp should turn up in the same areas (indeed it is found in Texas but is thusfar considered absent from Arizona and Florida).

Females of the solitary Pachodynerus nasidens build mud cells inside the abandoned nests of mud daubers (Sceliphron caementarium and Trypoxylon politum), or in other pre-existing cavities. It has been rumored that the females sometimes build their own free-standing mud nests, and these images would tend to substantiate that supposition. Inside, each cell is provisioned with paralyzed caterpillars that will be the food for the single larval wasp that develops there.

Enemies of this wasp are many, and include at least one species of cuckoo wasp in the genus Chrysis. Recall that cuckoo wasp females lay their eggs in the nests of other wasps. Melittobia chalybii, a tiny parasitic wasp in the family Eulophidae is also known to infest the nests of P. nasidens. Likewise, the sarcophagid satellite fly Amobia floridensis can infiltrate a nest, depositing her tiny larvae there. Acrobat ants (Crematogaster sp.) are recorded as predators, presumably breaking into nests to prey on the immature stages of the wasp. Wedge-shaped beetles in the family Ripiphoridae, genus Macrosaigon carry out their bizarre life cycle inside the nests as well.

There is another species of Pachodynerus found here in Arizona: P. guadulpensis. Older references list it as P. praecox. It ranges into from Mexico into southern California, Arizona, and Texas. Note the extra yellow stripe across the *front* of the abdomen that distinguishes this species from P. nasidens. The specimen imaged above was discovered in the butterfly garden at the Tucson Botanical Gardens in the middle of Tucson.

I’m hoping to learn more about these wasps, and complete my findings on the mimicry ring, sometime in the not-too-distant future. Meanwhile, please share your own observations here, and in your own blogs.

Wasps to the Rescue

Lest you think that wasps are no more than a novelty of nature, or at best natural pest control agents, take a look at this article in the New York Times. Many thanks to my friend Art Evans for sharing the story of the “Wasp Hound” on Facebook.

I have another personal friend who is (or was) engaged in similar research whereby certain insects could be reliably employed to detect explosives, and/or search for human survivors amid piles of rubble too inaccessible or unstable for firefighters and EMTs to negotiate. There is real potential here and it would literally pay to continue refining the capabilities of “bugs” to aid in the war against terrorism.

The only question I have after reading the above article is “So what species of wasp are you using?!” Details, details…