http://www.nytimes.com/2006/07/27/us/27butterflies.html?th&emc=th
July 27, 2006
In Texas, Conditions Lead to a Rabble of Butterflies
By RALPH BLUMENTHAL
Correction Appended
GOLIAD, Tex., July 25 ?- For a moment, Carol Cullar thought she was seeing fall leaves gusting down the highway south of Quemado, Tex., on the Mexican border.
But it is blistering midsummer, Ms. Cullar, director of the Rio Bravo Nature Center in Eagle Pass, realized. And leaves would not all be flying north at two or three feet off the ground ?- car radiator height.
These were butterflies. At least 200,000 of them, she guessed, perhaps a half-million. It was an invasion, she said, "like nothing I've ever seen."
South Texas is under siege from swarms of airborne migrants: tens of millions of Libytheana bachmanii larvata ?- snout butterflies to y'all ?- along with Kricogonia lysides, or yellow sulfurs, that have taken advantage of an unusual drought-and-deluge cycle to breed in spectacular if not record profusion.
The smallish, dull-colored snouts take their name from an appendage they attach to branches to disguise themselves as leaves.
Blinded drivers who have to pick the literally low-down critters off their grilles to avoid dangerous engine overheating are less than enthralled, as are the mottephobes, who fear butterflies and moths. But lepidopterists are thrilled with the spectacle, which they predict may be only the beginning of a population explosion of snouts.
They concede, however, that it could denude considerable swaths of Texas hackberry trees and other choice caterpillar habitats, at least for a while.
"Snouts, I'm at a loss for words," wrote Joshua S. Rose, a biologist and dragonfly specialist with the World Birding Center at Bentsen-Rio Grande Valley State Park near Mission, Tex., in an e-mail message to friends Tuesday.
"They're beyond any mere collection of individual animals," Dr. Rose wrote. "Like a flock, herd, swarm or even horde, they have more in common with a geologic or climatic force, the Gulf Stream or an Arctic front. While driving, we can't dodge butterflies, we can only aim the car at the parts of the road where the density is lowest."
Lawrence E. Gilbert, professor of integrative biology and director of the Brackenridge Field Laboratory at the University of Texas, said such mass emergences were hardly known outside the Southwest, although they also occurred with another butterfly species in Africa. Dr. Gilbert filled a bucket last week with hundreds of dead snouts and sulfurs collected from a roadside near Alice, many of which never made it to the end of their two-week life span.
The phenomenon sent Mike Quinn, an entomologist with the State Parks and Wildlife Department, beelining here on Tuesday from his Austin office to track the butterfly migration.
Cellphone pressed to his ear, Mr. Quinn, 43, polled area rangers for promising sightings. He had high hopes along the reservoir at Choke Canyon State Park. "We were told this was snout central," he said. But they had since fluttered by.
"Tons? Right as we speak, or the last few days?" Mr. Quinn asked another tipster. "Let me get a specific from you. Exactly where is everywhere?"
One parks employee, Linda Lopez, tried to be helpful. "The snout ones are the little brown ones with variegated color?" she asked.
"You got it," Mr. Quinn said. "We're looking for the river of butterflies, not just the stream."
Driving a circle of perhaps 200 miles from Goliad around Choke Canyon and back, Mr. Quinn never did find a real swarm, although he was tantalized by evidence of their ubiquitous presence on the radiators of tractor-trailers, emblazoned with crazyquilt pastiches of dead-butterfly art.
But he stamped through the brush along the water, flushing clouds of snouts, sulphurs and little blues of the kind favored by Vladimir Nabokov, which all fluttered excitedly around him. He also saw considerable evidence of the stripped Celtis trees that had nurtured the caterpillars, and specks of black caterpillar droppings called frass that fertilize the vegetation and help it recover from the feeding frenzy.
"Frass happens," Mr. Quinn said.
Mr. Quinn and Dr. Gilbert said the butterfly proliferation had been set off by drought conditions that decimated the caterpillar's natural predators, followed by drenching rains that prompted hackberry trees to put out green shoots, quickly attracting the egg-laying caterpillars that could briefly thrive without enemies.
"It was a double pop," Dr. Gilbert said, two cycles in succession that reinforced the effect over the 12-day passage of egg to adult.
With insects generally suffering a 99 percent mortality rate, said Mr. Quinn?- that is, only 1 egg of 100 laid making it to maturity ?- a sudden improvement in the odds can radically disrupt the usually exquisite balance of nature.
Where, how and why the swarms migrate is less clear. Butterflies are not social creatures flying in flocks like birds but are drawn to flowers as sources of nectar and pollen.
Dr. Gilbert said that in studying migrating snouts he was struck to find that up to 95 percent were males. "The older males get most of the matings as the hatch continues," he theorized. "Then the new guys don't have a shot because of the old guys, and they just say, The hell with this, and they go."
Correction: July 28, 2006
An article yesterday about an abundance of butterflies in South Texas misstated a step in butterfly reproduction. It is the butterfly itself, not the caterpillar, that lays eggs.
