July 27, 2006
In Texas, Conditions Lead to a Rabble of Butterflies
By RALPH BLUMENTHAL
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 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.
But he stamped through the brush along the water, flushing clouds
of snouts, sulphurs and little blues, which all fluttered excitedly
around him. He also saw considerable evidence of the stripped
trees that had nurtured the caterpillars, and specks of caterpillar
droppings called frass that fertilize the vegetation and help
it recover from the feeding frenzy.
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.”
Copyright 2006 The New York Times Company
S. E. Anderson
author- "The Black Holocaust For Beginners" a Writers and Readers
book
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