SAN ANTONIO -- Swarms of butterflies take over San Antonio, but they’re not Monarchs.

You might have already met the snout nose butterfly and not know it. They arrived in mass in South Texas a few days ago, taking over neighborhoods and flooding roads all over the northwest side.

The University of Texas at San Antonio butterfly expert Tyler Seiboldt said the weather has been perfect for swarms of them to stop in San Antonio. A summer drought killed off its natural predators.

In the last few weeks, rain in the San Antonio area gave birth to an ample source of snout nose butterfly food.

“The hackberry plant which is really their host plant, they use for reproduction a lot of the time, is really driving their movement through the City of San Antonio,” Seiboldt said.

Many people saw the flutters around town and assumed they’re Monarchs. The Monarchs won't be in town until late October, early November. The snouts are heading south, but they're not as deliberate as the Monarch, which comes through every year, leaving Canada and the Northern United States on their way to Michoacán, Mexico, where they will spend the summer.

“They're moving south, but their migration really isn't quite as focused as some other species, like the Monarch butterfly where it had a direct location that they're heading towards,” Seiboldt said. “It's really driven by the availability of these hackberry plants.”

Snouts don't come through San Antonio every year, only if the conditions are right for them to have plenty of food in San Antonio. UTSA's butterfly expert predicts they'll be here for a few more days and move on.