YOLO COUNTY (CBS13) — If you’re driving along the Yolo Causeway right before dark, you could be in for quite a sight as hundreds of thousands of bats make their daily flight from under the highway to their hunting ground.

The mass flight of bats called a batnado can only be seen during the summer months, but experts say bat season came early this year.

As unsuspecting drivers travel between Davis and West Sacramento, underneath them is a makeshift bat cave for more than 250,000 bats.

“They’ll get themselves tucked in really tight—sometimes three deep,” said Corky Quirk. “It’s like a big massive bat house—three-mile bat house.

Qurk, affectionately known as The Bat Lady, says the Mexican freetail bats call the underpass home during the summer in Sacramento. They hang out because of nearby food from rice fields that provide plentiful insects.

“They arrive as our weather changes and our insect load gets high,” she said. “This time of year we have all the adults and the juveniles out there hunting.”

Every evening just before dark, they round up the troops, and like a ribbon across the sky, head out for the hunt.

“Some of these bats are going to go one to two miles high hunting migrating moths,” she said.

But while the bats like the heat, the drought has caused many of the pups to be born two weeks earlier than usual, and the lack of water has proven to be problematic for some.

“I’m getting more calls this year about people scooping bats out of their swimming pools, and I think it’s because bats are thirsty and they are looking for water,” she said.

But for now, Quirk says there’s still enough foot to keep the batnado buzzing every evening, at least this year.

The bats should start heading south in search of warmer weather around mid-September. The most accessible place to see the batnado is on the Davis side of the causeway near the entrance to the Yolo Bypass Wildlife Area.