Narcisse, Manitoba ? At first glance it’s just a hole surrounded by aspens in glowing spring leaf. Then you notice the ground is moving.

From every crack in the limestone bedrock, snakes slither by the thousands, some tangled into balls, rolling over rocks and tree trunks, starved for love after hibernating through the seven-month Manitoba prairie winter.

Dozens of sex-crazed males wrap themselves around females in hopes of getting chosen to mate, watched by crowds of tourists who have trekked three miles on foot.

“It’s a snake ball! It’s a bowling snake ball!” yelled Michael Moloney, clutching a handful of serpents on a visit for his 8th birthday.

Resembling mythical Medusa’s snake hairdo, the tangles of red-sided garter snakes are one of the more unusual wildlife occurrences of North America, attracting thousands of spectators during the monthlong migration.

“There’s nothing else out here but the snakes,” said Darlene Herron, who sells snacks from a trailer in the parking lot of the remote region between Lake Winnipeg and Lake Manitoba, 420 miles northwest of Minneapolis-St. Paul, Minn.

The crowds start showing up on Mother’s Day, she said, though, “I don’t know why anyone brings their mother to the snake dens.”

Eight-year-old Michael Moloney checks out a bundle of snakes that he caught with a little help from 6-year-old Reilly Onufreychuk. The boys met last month at Cave No. 3 at Narcisse Snake Pits Wilderness Park in Manitoba.

Nobody knows exactly how many red-sided garters come out of the Narcisse snake dens each spring. A conservative estimate is 50,000.

The snakes go five to eight feet underground in the fall to keep from freezing, spending months jammed in dank, dark crevices with no food beneath the frost line.

When warmer temperatures beckon, they climb out hungry for frogs and toads to eat and the chance to mate with a longer, thicker female.

Once the female has chosen a male, the mating ball unravels and the spurned males look for another partner. Baby snakes are born in the late summer, usually 20 to 50 at a time, with an estimated 2 percent surviving to adulthood.