COMAL COUNTY (CBSDFW.COM) – Bats have long been associated with Halloween but the mammals are more than just nocturnal flying creatures… they have a major impact on agriculture and even Texas tourism.

The world’s largest bat colony is in Comal County — just outside San Antonio.

Just off a dusty road in south Texas, nestled in a nature preserve, a sunken cave draws a crowd.

Around dusk each day the wildlife at the Bracken Cave Preserve perks up, signaling to the animals and people who visit that they’re in for a show.

“Oh, they’re like coming out!” visitor Sam Michaels shouted.

The experience — known as the emergence — literally envelopes its audience. “They’re [bats] everywhere,” Michaels said. “There are so many of them, it’s like unbelievable.”

“These emergences are so intense — they show up on the Doppler radar like clouds forming over these bat roosts,” said Fran Hutchins, director of Bat Conservation at the preserve.

But make no mistake, the millions of swirling bats are on a mission.

Hutchins says the Mexican free-tailed bats can eat nearly 150 tons of bugs a night. “Not having bats is a world with a lot of biting bugs,” he declared.

The bats can fly as high as 10,000 feet and travel 60 miles away from the cave while hunting for food. The foraging in turn helps Texas farmers.

Bat biologists have estimated the night flying creatures can save farmers billions of dollars in pest control annually nationwide.

Cotton is one of the crops that benefits most, along with corn, sorghum, and even Texas pecans.

John and Jimma Byrd, owners of a pecan orchard in Central Texas, built a bat house after discovering they had several species of bats on their farm.

“We built one and sure enough they started coming,” John said. “They’re working every night too. You don’t have to pay them and they don’t ask for nothing but a place to live.”

It’s a win-win for the couple who farm organically.

“All the old time pecan farmers used to say that the bats were good for an orchard,” John said.

Jimma explained, “So what we’re doing is not really anything so new, it’s really something that’s really old.”

Few actually witness the bats work‚ since their efforts happen in the dark of night.

Back at Bracken Cave the bats begin to return just before dawn. Watching, Hutchins said, “It’s raining bats into the cave right now.”

The millions of bats that live at Bracken Cave have now made their way to Mexico, where they’ll spend the winter. They will return to Comal County in the spring.