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…

Wasp Wednesday: Brachygastra mellifica

I recently had the honor of reviewing an article about wasps destined for a national magazine. One of the few inaccuracies I found was the assertion that while bees make honey, wasps do not. Putting aside the fact that only social species in the family Apidae make and store honey (the vast majority of bees are solitary and do not manufacture honey), it is also incorrect to say that no wasps produce this sweet substance. Case in point: Brachygastra mellifica, a tropical social wasp that sneaks over the border into Texas and possibly Arizona.

Known as the “Mexican Honey Wasp,” this species is a member of the family Vespidae and the subfamily Polistinae. They are small insects, only 7-9 millimeters in length. The specimen imaged here is one I spotted at a trailer park resort in Mission, Texas, adjacent to Bentsen-Rio Grande Valley State Park. It was one of several different hymenopterans lapping up honeydew from an aphid-infested shrub.

While the wasps themselves may be diminutive, their paper nests are not. A large nest can be a foot in diameter and composed of up to 50,000 individual cells. The paper combs and envelope are contiguous, the cells being very shallow. Honey is stored in uncapped cells, unlike in honeybee colonies where the storage cells are capped with wax. Nests, usually constructed in low trees, can be occupied for years in the tropical and subtropical climate favored by the wasps.

Brachygastra mellifica is considered to be a mostly docile species, but one would still be wise not to antagonize a nest. Dr. Joan Strassmann, Harry C. and Olga K. Wiess Professor in the Department of Ecology and Evolutionary Biology at Rice University, warns that they “….can explode, attacking en masse.” Considering that an average nest can house between 3,000 and 18,000+ worker wasps, it pays to exercise caution.

Still, the prospect of getting stung multiple times has not deterred people from exploiting these wasps since ancient times. Several references exist that document the harvesting of honey from nests of Brachygastra species (there is more than one) by indigenous peoples in Brazil and Mexico. More recently, rural peoples may transplant small nests into their yards and gardens, allowing the colonies to expand, then routing the resident wasps with smoke and destroying the combs for the honey. The wasps will re-build and start the cycle anew. You eat the honey at your own risk. Nectar collected by the wasps from plants like Jimsonweed (Datura) can translate into toxic honey.

Humans are not the only animals that covet the wasps’ cache of honey. Woodpeckers are known to break into the nests for the sweet stores of honey, and small mammals probably pilfer honey as well.

I want to thank Matthias Buck at the Royal Alberta Museum in Edmonton for identifying my images as being the species Brachygastra mellifica. There is a solitary species of vespid wasp that looks virtually identical to B. mellifica. Mexican Honey Wasps are easily distinguished by their petiolate abdomen (read “wasp waist”), but the petiole is short and nearly vertical, making it difficult to detect in live, moving specimens. Tune in next week when I’ll introduce that solitary imposter!

Sources: A great, in-depth article on the Mexican Honey Wasp can be found at the Texas Entomology website. Additional links can be obtained at the BugGuide species page.