Fly Day Friday: The Good Mosquito

Believe it or not, there is a mosquito species I look forward to seeing every year. You may think I'm crazy, but hear me out. There are at least three reasons to love elephant mosquitoes in the genus Toxorhynchites. They are pretty, beneficial in the larval stage, and do not bite as adults.

A male Elephant Mosquito

Elephant mosquitoes are also known as giant treehole mosquitoes, so you can sense a theme here. They are indeed large for mosquitoes, averaging about seven millimeters in body length. That does not include the mouthparts and antennae. Their long legs make them appear larger still. Why the name "elephant mosquito?" It may be a reference to the long, upcurved palps of the males, which suggest elephant tusks.

Notice the tusk-like palps (part of the mouthparts), and bushy antennae on this male.

There is no denying the beauty of our single North American species, Toxorhynchites rutilus. They are iridescent blue and purple, with silver and gold highlights, and white tips on the hind legs. It seems that no one photo captures all the colors all at once. Despite their brilliance, they are surprisingly cryptic in the dimming light of dusk, when they are most active (though they are considered day-fliers).

As their other name indicates, elephant mosquitoes breed mostly in water-filled treeholes. The larval stage, at least in later instars, is predatory on other aquatic insects, including....wait for it....the larvae of other mosquitoes. Yes, you heard that correctly, they are a natural biological control of the mosquito species that pose a threat to human health. The larvae are reddish in color, with a short anal siphon (bearing the spiracle that permits intake of air at the water surface), and a broad, black head with strong mandibles. There are four larval instars, an instar being the interval between molts.

The female Elephant Mosquito has straight palps, and simple bristle-like antennae.

The adult elephant mosquito has a distinctive proboscis, bent strongly downward near the middle of its length. Instead of using their beaks to draw blood from other animals, elephant mosquitoes of both sexes feed only on flower nectar. As flower visitors, they are also pollinators of wildflowers. Some other species in the genus may also feed on fruit juices, and honeydew (the sugary liquid waste of aphids, scale insects, and various planthoppers).

The female again, showing that long,sharply-curved proboscis.

Here in northeast Kansas, on the Missouri border, I have found Toxorhynchites rutilus only in late autumn, and only on the flowers of White Snakeroot. I have only seen them in our yard, in fact, but I am not usually exploring elsewhere as sunset approaches. The species ranges from the eastern half of Texas and Oklahoma diagonally northeast to southern Pennsylvania, Connecticut, and Delaware.

Can you tell which sex this one is?

There are roughly eighty species of Toxorhynchites, occuring mostly in tropical regions around the globe. Due to their unique appetite for other mosquitoes, they have been employed as biological controls for container-breeding mosquitoes in Japan, southeast Asia, the Caribbean, and in some cities in the United States.

Are you a new fan of elephant mosquitoes yet? If not, please see the resources and links below for additional information on the biology of these remarkable flies. Mosquitoes, like most insects, and people, defy neat categorizing as "bad" or "good." Entomology is a great place to learn lessons like that.

So handsome!

Sources: Alomar, Abdullah A. and Barry W. Alto. 2022. "Elephant Mosquito Toxorhynchites rutilus Coquillett, 1896 (Insecta: Diptera: Culicidae)," Ask IFAS EENY-787/IN1380. University of Florida.
Coin, Patrick, et al. 2004. "Species Toxorhynchites rutilus - Elephant Mosquito," Bugguide.net
Donald, Claire L., Padet Siriyasatien, and Alain Kohl. 2020. "Toxorhynchites Species: A Review of Current Knowledge," Insects 11(11): 747.
McAlister, Erica. 2017. The Secret Life of Flies. Buffalo: Firefly Books. 248 pp.
Ricciuti, Ed. 2019. "Meet the Mosquito With a Big Appetite - for Other Mosquitoes," Entomology Today.

Wasp Wednesday: Purslane Sawflies

Not all wasps sting, and not all feed on other insects in their youth. The larvae of sawflies are vegetarians, and many are mistaken for caterpillars. You need not venture far to find sawflies, either. I found the adult female specimen below in my own backyard on the evening of September 18. Through a little detective work I discovered she is a Purslane Sawfly, Schizocerella pilicornis, in the family Argidae.

This species is unique among all argids (worldwide) in that its larvae feed internally on the host plant, mining inside the leaves of purslane. Until recently, it was thought that some larvae of S. pilicornis feed externally. Analysis of mitochondrial DNA has demonstrated that those leaf-nibbling larvae belong to a separate species, S. lineata (Hartsough, et al., 2007).

Adult females can be distinguished by the amount of black markings on the top of the otherwise red (or orange) thorax. Females of S. pilicornis have a solid, or nearly solid, black stripe down the center of the thorax, constricted in the middle. Females of S. lineate have very reduced black markings along the midline of the thorax. S. lineate is also slightly larger, females averaging about 7 millimeters to the 5-6 millimeter length of female S. pilicornis.

Both species are widespread in the New World, ranging from southern Canada to at least Central America. S. pilicornis occurs at least as far south as Argentina. U.S. records for S. pilicornis include Arizona, California, Colorado, Connecticut, Washington, DC, Florida, Indiana, Iowa, Kansas, Maine, Maryland, Michigan, Minnesota, Mississippi, Nebraska, New Hampshire, New Jersey, Ohio, Oregon, Texas, Virginia, and Washington. The species may actually be adventives here, and native to South America. At least, it was not described from North America until 1900.

Life history information may be open to debate since it comes prior to the realization that two species are involved (Gorske, et al., 1977). Females lay one egg per leaf, inserting the ovum into the foliage with the saw-like ovipositor that gives sawflies their common name. Larvae feed for roughly six days, going through five instars (an instar is the interval between molts). Mature larvae tunnel into the soil to a depth of about 3.5 centimeters where they pupate. Adults emerge a week later (during the summer generations; otherwise they overwinter as pupae). Their lifespan as adults is apparently very short, only 24 hours according to one source (Gorske & Hopen, 1976).

There can be up to six or seven generations annually, at least in Illinois, where these insects exert a small degree of biological control against purslane.

Males in this genus are easily identified by the last antennal segment, which is forked. It looks like the insect has four antennae instead of the two it should have.

I have found numerous males, and this one female, “sleeping” out in the open on grasses and other vegetation at sunset. Many wasps (and solitary bees) can be found by looking in fields and meadows for sleeping individuals at dusk, in the early morning, or during inclement weather.

Sources: Gorske, S.F. and H.J. Hopen. 1976. “Purslane sawfly (Schizocerella pilicornis) as a biological control agent of Common Purslane (Portulaca oleracea L.),” a paper presented at the 73rd annual meeting of the American Society for Horticultural Science, August, 1976.
Gorske, S.F., H.J. Hopen, and R. Randell. 1977. “Bionomics of the Purslane Sawfly Schizocerella pilicornis,” Ann. Entomol. Soc. Am. 70(1): 104-106.
Hartsough, Chester D.B., Edward F. Connor, David R. Smith, and Greg S. Spicer. 2007. “Systematics of Two Feeding Morphs of Schizocerella pilicornis (Hymenoptera: Argidae) and Recognition of Two Species,” Ann. Entomol. Soc. Am. 100(3): 375-380.