What may appear to some to be a butterfly invasion in South Central Texas is really just an annual migration of the American snout butterfly, said Molly Keck, Texas A&M AgriLife Extension Service entomologist for Bexar County.
"Right now these snout butterflies are migrating through the region in huge numbers on their way toward the Rio Grande River area," Keck said
She said the insect gets its name from the elongated mouthparts called "palps" that extend from the head.
"They are small- to medium-sized butterflies that are much smaller than a monarch and also a bit smaller than a painted lady," Keck explained. "They have orange and brown markings and blend in perfectly with the bark of trees. When flying, they can look like a small leaf fluttering in the wind."
Keck said each year snouts make their migration, but their numbers correlate with the amount of rainfall and moisture available. She said other butterflies may be mixed in with the snouts, such as sulfurs and possibly some brush-footed butterflies, but those migrating in large numbers are most likely the American snout.
"This year we had rain at the right times to help their population," she said. "What the rain actually does is increase the number and size of leaves on the tree that are the snouts' primary food source – the spiny hackberry. With more food, the females lay more eggs in the summer. Those eggs hatch and the caterpillars eat the new growth."
She said the caterpillars can only eat new growth from the spiny hackberry because it is tender enough for them to chew.
"This population explosion we are seeing is the result of those caterpillars becoming pupa and emerging to migrate down south," she said. "Migration is often during late summer to early fall. And it isn't uncommon to see these butterflies migrating in large numbers."
Keck said South Central Texas residents can expect to continue seeing the snout migration throughout early fall.
"In some years, we see two generations migrating before the fall is over," she said. "I suppose time will tell if that will occur this year."
Keck said while the snouts can be annoying and leave a mess on a car during a road trip, there is really no way to avoid them and they do serve a positive environmental purpose.
"Like bees, butterflies are good pollinators and provide a service to both agriculture and the homeowner through plant pollination," she said.
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