The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Sunday, December 04, 2005

Snout Butterflies Are on the Increase
by Ro Wauer

During the last couple weeks, American snouts have increased dramatically in my garden and the surrounding area. But that is nothing like the masses that were recorded further south in Texas a few weeks ago. An estimated 7.5 million snouts were reported in the Alamo area of the Lower Rio Grande Valley on September 5. And there is a chance that our numbers will continue to build over the next few weeks, at least until the really cold weather sets in.

Mass movements of snouts occur every few years, and some of those can be truly amazing. One of the most spectacular swarms was recorded in September 1921 when an estimated six billion (6,000,000,000) individuals were involved. Approximately 25 million snouts per minute were recorded moving southeasterly over a 250 mile front from San Marcos to the Rio Grande Valley. That flight lasted 18 days.

Snout behavior of this kind was first recognized in 1983, according to Mike Quinn in a fascinating article (, as being most closely related to "the intensity and duration of dry periods immediately preceding drought-terminating rains." A 1985 study by Larry Gilbert, University of Texas, revealed that snout population explosions were related to leafing out of the snout's primary host plants, spiny hackberry, as well as diminished numbers of parasites that would normally keep snout populations in check. Female snouts take advantage of new spiny hackberry growth to lay eggs which soon hatch into caterpillars that feed on the tender leaves, often defoliating their hosts. Following emergence from the chrysalis, all within the same timeframe, the adult snouts begin moving southward, producing some of the greatest known insect immigrations.

Snout butterflies are considered dead leaf mimics, because they possess a snout, actually the butterfly's labial palps that extends for several millimeters beyond the eyes. This feature is extremely unusual in butterflies and so snouts are classified within the unique Subfamily Libytheinae. They are rather small butterflies, only half again larger than most hairstreaks and blues, with a fascinating wing pattern. Their underside, most often seen as they usually perch with closed wings, is mottled gray, brown and blackish, while their upperside is brown and orange with white forewing spots; the wingtips are square. The open wing pattern is most likely to be observed during mornings and afternoons when perched with spread wings to absorb warmth from the sun. But it is the butterfly's long snout that is most distinct.

The snout's overall range corresponds to that of the spiny hackberry, that occurs only from South Texas west through southern New Mexico and Arizona. However, snouts also occur throughout much of Texas because they can utilize other hackberry species. But it very rarely ever occurs in numbers as it does in South Texas where spiny hackberry, also known as desert hackberry or granjeno, occurs in abundance.

The relationship between snouts and its larval foodplants is not unique. The same can be said for the majority of insects. A butterfly's breeding range is limited to that of its larval foodplants. However, because butterflies are such marvelous fliers, the monarch that can migrate several thousand miles is our best example, they can appear at locations many miles from where they emerged. And many southern butterfly species wander northward, especially in fall. Currently, my garden hosts a number of more tropical species, including Julia heliconian, white peacock, and common mestra.

Of course, American snouts are there in numbers, nectaring alongside the two dozen other butterfly species that are taking advantage of the flowering shrubs that I have planted for just such an occasion.


At 10:55 PM, Anonymous Genie said...

Where do they migrate from and to? Or do they migrate at all? We're surrounded by them at the moment, I think. I'm not positive, but I think it's the snout butterfly that's filling every square inch of our air in Kinney County, Texas right now.


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