AUSTIN (KXAN) — What’s the deal with all the butterflies?

There has been an increase in butterflies in the area this fall, and the unusually hot and dry weather this summer is to blame.

The unusual insect is known as the American snout butterfly, so named because it has a “prominent ‘snout’ formed by elongated mouthparts,” according to Texas A&M’s Agrilife Extension.

Dan Hardy, president of the Austin Butterfly Forum, explained the influx of the butterflies.

We’re seeing a lot of butterflies called snout butterflies, the American Snout,” Hardy said. “And it’s kind of an exciting time of the year for us because we have these giant explosions of these butterflies that come out of South Texas and Mexico, stream through Austin and kind of hit north, northeast.”

Hardy said the insects appear about once or twice every couple of years, and they are harmless to people. He said they feed on hackberries, which grow on large deciduous trees and are a member of the elm family.

“This year’s movement is a good one,” Hardy said. “Although in past years, there’s been, you know, humongous movements, sometimes hundreds of thousands or millions come through where they’ve been counted.”

According to Texas A&M, the butterflies are known for their mass migrations northward when their numbers explode in the south and southwest, and their populations can be such that they “darken the sky.”

“It’s kind of a phenomenon, and people note about this for decades,” Hardy said.

He said the occurrence is related to weather in South Texas and northern Mexico, where drought can kill the predators that hunt the snout butterflies. Hardy said when heavy rain arrives, eliminating the drought, there’s then “a huge flush of growth” on hackberry trees.

“The snouts lay their eggs on these new hackberry leaves, and they just reproduce profusely,” he said.

Hardy explained that the trees, in turn, become “completely denuded of leaves.” He said the butterflies pupate and the adults emerge to “discover that all the leaves are eaten in that area,” forcing them the migrate.

“There’s no leaves; there’s no food. So they will immigrate, migrate … just flood out of that area, going all different directions, but particularly north,” Hardy said. “Then they’ll hit areas like San Antonio, Corpus, Austin.”

The university said one of the larger migrations was reported in September 1996, when “countless butterflies were observed flying across highways” south of San Antonio.

Snout butterflies produce up to four generations per year, according to the university.