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Earlier this week, Jessica Beckham stood in her backyard and watched a stream of brown and orange butterflies floating overhead.
“I was seeing them just fly over, and you have to look up and say, ‘Wow, this is amazing,’” said Beckham, an entomologist who teaches environmental science classes at the University of Texas at San Antonio. “And then I start to worry about them getting smashed by cars.”
The mass emergence of American snout butterflies over the past week has captured San Antonio’s attention, mostly in the form of butterflies smacking into drivers’ windshields. In a region without many fall colors, the flittering streams of millions of butterflies almost serve as a South Texas version of autumn leaves.
Many locals call the emergence of these butterflies a migration, perhaps because their appearance seems to coincide with the arrival of monarch butterflies in San Antonio. In fact, snout butterflies are here year-round, according to Molly Keck, an insect and bug expert with Texas A&M AgriLife Extension.
“It’s not really a true migration because there’s no end-point,” Keck said. “If you stand outside, it will seem like they’re going in one direction, but they’re not.”
When temperatures cool, snouts spend the winter in a semi-hibernation known as diapause. They overwinter as adults, not as eggs, “which is kind of unusual for an insect to do,” Keck said.
In Texas, snouts tend to boom in places that host their caterpillars’ favorite food. Snout caterpillars can feed on several different hackberry species, but their preference is the shrub-sized spiny hackberry, native to South Texas roughly from Travis County south and to parts of the Big Bend region.
Snout outbreaks come when summer droughts knock back parasites that keep snout populations suppressed, then rain brings new leaf growth that supports a boom in caterpillars. What can follow, especially from Labor Day through November, is the emergence of likely millions of adult butterflies.
“It’s just rain allowing for the hackberries to have good green growth,” Keck said.
As adults, snouts are pollinators that feed on a variety of nectar plants. To attract snouts and other butterflies, residents can plant native species like sages, sunflowers, and Gregg’s mistflower.
“They’re generalists,” Beckham said. “They’re not going to go for just one particular plant.”
The species is a brush-footed butterfly, part of the same family that includes monarchs and 6,000 other lesser-known species such as queens and pink ladies.
Every insect has six legs, but brush-footed butterflies stand on only four. Their two forelegs evolved to be short and hairy, used for touching and tasting instead of walking or perching.
Interestingly, the snout doesn’t use its jumbo-sized snoot to feed. It has a curled-up proboscis, same as many other butterflies. It can unfurl this proboscis to suck up nectar, water, or minerals. Here’s a video showing a snout’s proboscis in action.
Instead, biologists say its wings, which are drab when folded, effectively camouflage the snout as a dead leaf, with the butterfly’s long mouthparts and antennae mimicking the stem of the leaf. Still, birds, lizards, and other species tend to prey on them, Keck said.
“Their population’s so high, so it’s part of the natural cycle of things,” she said.
This article has been updated to remove an incorrect reference to the overwintering behavior of monarch butterflies.