IT’S RUSH HOUR in Philadelphia for thousands of baby toads as they hop across a busy residential street on a rainy summer night.

Why do toadlets cross the road? To get to the woods on the other side — where they will live, eat mosquitoes and grow up to be full-sized American toads (bufo Americanus). After a couple of years, they’ll make the reverse trek as adults — unless they get squashed by a car.

That’s where the Toad Detour comes in.

The Schuylkill Center for Environmental Education sets up a roadblock each year in the Roxborough neighborhood, rerouting cars so the amphibians can cross the two-lane street without fear of, um, croaking.

The cycle starts in early spring when adult toads, which can fit in the palm of your hand, emerge from the woods to breed. They cross Port Royal Avenue, scale a 10-foot-high embankment and then travel down a densely vegetated hill to mate in the abandoned Upper Roxborough Reservoir. Their offspring — each about the size of a raisin — make the journey in reverse about six weeks later.

Cars pass a toad crossing sign in the Roxborough neighborhood of Philadelph Apexchange Apexchange

So many baby toads were on the move on Monday evening it looked like the road’s muddy shoulder was alive. Volunteers scooped them up in plastic cups and deposited them on the habitat side of the street.

“I didn’t expect at all that there were going to be so many of them in one area,” said 17-year-old Kaitlyn Hunt as she held a cup with more than a dozen toadlets. “And they’re so tiny. They look like bugs.”

The detour program began in 2009 when a local resident noticed the toad-filled road. City officials later granted permission to close the street for a couple of hours every evening during both two-week migration periods.

Organizers estimate they helped about 2,400 adult toads cross the road this spring, said volunteer coordinator Claire Morgan. And because female toads can lay thousands of eggs, many more toads are migrating the other way and need protection.

Though some will inevitably be squished when the roadblock is not up, the toad population is not endangered, Morgan said. But protecting wildlife is important, she said, and local residents seem to support the project — especially after they volunteer to help.

“We get some people that question it,” said Morgan. “But after they do it, they’re hooked.”

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