Tuesday, May 30, 2017

Window-winged Moths

One is not accustomed to thinking of moths as day-flying creatures, but a surprising number are indeed diurnal. You may simply not always recognize them as moths. A good example are the window-winged moths in the family Thyrididae. They are named for square or rectangular translucent spots in their wings, which may appear to be white or amber in color.

I encountered one of these diminutive insects just the other day, Monday, May 29, in Aiken Canyon Preserve, a property of The Nature Conservancy that features mixed conifer (mostly Ponderosa Pine and juniper) forest, impressive sandstone bluffs and formations, and extensive glades of prairie grasses, yucca, cacti, and herbs. The trail crossed a dry stream bed at one point and I caught sight of something I first thought was just another fly. It landed briefly and revealed itself to be Thyris maculata, a relatively uncommon western insect, but much more widespread in the eastern U.S.

The little moth was perhaps seeking water and/or minerals and was barely pausing, preventing me from getting really crisp images. When I returned home I did a bit of research and found that there are only twelve (12) species in the family Thyrididae known in North America, and few of those are western. The family is mostly pantropical (Old World and New World tropics), and the total number of world species exceeds 760. There are, in fact, over 400 additional species awaiting description at the London Museum of Natural History alone. While our domestic species have a wingspan varying from 6-16 millimeters, many tropical species are larger, with wingspans of 26-34 millimeters.

Thyris maculata from Massachusetts

Thyris maculata does visit flowers for nectar, as I observed in the town of Athol in western Massachusetts in 2015. Even then, the little moths defy attempts to get in-focus pictures. You are more apt to find at least some species, like the "Mournful Thyris," Thyris sepulchralis, licking animal scat. Fresh dung is a real treasure to lots of insects, including many butterflies and true bugs.

What do they eat in the caterpillar stage? They are surprisingly cosmopolitan in their tastes, being generalist feeders. Among their host plants are beans, grapes, cotton, and thoroughworts. The larvae typically roll the leaves of the host plant and tie them with silk; some species bore in the stems or twigs of the host. Thyris maculata has been reared from Clematis and Houstonia. This might explain the moth's extensive range, from Ontario and Quebec south and west to Georgia, Texas, Missouri, New Mexico, Colorado, and even Idaho and Montana. The adult flies anytime between March and October, but especially May through July. Samuel Johnson, a friend and moth expert here in Colorado deduced from my record yesterday that the species has two broods in the Pikes Peak region of Colorado. His own record is from August, 2003.

Dysodia sp. from Rio Rico, Arizona

Yet another genus of window-winged moths that I have come to know is Dysodia. These are slightly larger, heavier-bodied moths which are nocturnal. I have seen them attracted to lights in southern Arizona and the Lower Rio Grande Valley in southernmost Texas. The caterpillars typically roll the leaves of their host plant, forming both a shelter and a comfortable place to dine. There are at least four species of Dysodia in the U.S., and the one in south Texas is likely an undescribed species. So much yet to learn....

Thyris maculata from Massachusetts

Sources: Beadle, David and Seabrooke Leckie. 2012. Peterson Field Guide to Moths of Northeastern North America. Boston: Houghton Mifflin Harcourt. 611 pp.
Covell, Charles V., Jr. 1984. A Field Guide to Moths of Eastern North America. Boston: Houghton Mifflin Company. 496 pp.
Powell, Jerry A. and Paul A. Opler. 2009. Moths of Western North America. Berkeley: University of California Press. 369 pp.

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