If you see a foreboding cloud of bats flood the night sky this summer, don’t be spooked. This mass migration is not a bad omen but a glimpse at some of Arizonan’s most interesting creatures.

The National Weather Service reported a large emergence of bats from the Phoenix bat cave at about 9 p.m. on Sunday, drawing closer attention to the many bats in metro Phoenix and Arizona.

Bats are an important part of Arizona’s ecosystem and are much more common than you may think.

Here’s everything about the Phoenix bat cave and the creatures that reside there.

What is the Phoenix bat cave?

Angie McIntire, a bat biologist at the Arizona Game and Fish Department, said in an interview with The Arizona Republic there could be between 10,000 to 20,000 bats living in this unsuspecting storm drain.

But this tunnel is actually the ideal home for many species of Arizona bats. Insectivorous bats, whose diets rely heavily on insects, prefer to stay by long water sources that make skimming the water to catch prey easy, according to the Arizona Game and Fish Department. Since bats spend their downtime hanging upside down, the flood control tunnel’s rough concrete ceilings is the perfect surface to hang from.

Where is the Phoenix bat cave?

The Phoenix bat cave is located north of 40th Street and Camelback Road. Conveniently, you can walk to the top of the tunnel by following the Arizona Canal. Take the path on the north side of the canal for about 200 yards, past the office buildings and parking garage, to reach the perfect spot to watch the bats.

If you need to find parking, you can find the bat cave parking lot on Google Maps.

What is the best time to see the bats in Phoenix?

Every year, from May through October, thousands of bats migrate to Mexico. They start their journey southbound just before dusk, or 8 p.m. in the summer months, and continue into the night.

What is the most common bat in Phoenix?

Of the 28 different species of bats found in Arizona, Mexican free-tailed bats are the most common. The United States has a Mexican free-tailed population of over 100 million, according to the National Park Service.

According to another interview with The Republic with McIntire, Mexican free-tailed bats have been found congregating in huge numbers under several bridges in the Phoenix area. McIntire said the Gilbert Road bridge, where Gilbert Road crosses the Salt River, has approximately 30,000 in its structure.

Mexican free-tailed bats can be identified by their reddish to dark brown or gray fur, forward-pointing ears and wrinkled lips. These bats have narrow wings that typically span 12 to 14 inches, allowing them to fly at speeds of 60 miles per hour, according to the Arizona-Sonora Desert Museum.