You may not have thought this - if you thought at all about baby toads so small they can perch on a fingernail.

But toadlets are "amazing daredevils."

That eyewitness description is provided by Lisa Levinson, coordinator of the Toad Detour, which for the past several years has been helping adult toads every March to cross Eva Street and Port Royal Avenue to mate at a nearby reservoir in Upper Roxborough.

This year, Toad Detour volunteers are also looking out for the fruit of that endeavor, tiny toadlets hatched at the reservoir, as the amphibians as small as spiders make their way back across the roads to their home in the nearby woods.

The toadlets have been traveling by the thousands, many of them at dusk, on damp or rainy nights since Saturday, and will continue to do so for the next several weeks, Levinson said.

The small creatures, known as American toads, temporarily halt their migration during dry weather. But nothing else will stop them, Levinson said.

A 15-foot rock wall stands in their path, she says.

The toads "have been hopping right up to it, looking down and hopping off, and - geronimo! - at the bottom they seem to just right themselves and keep going," Levinson said.

The toadlets may be indestructible to natural obstacles, but, "one car will kill a thousand of them." Levinson said. "It's hard to see them. They look like insects, spiders or more like flies."

The Streets Department has again this year provided a permit for the group to detour cars around Port Royal when the toads are crossing.

Volunteers are badly needed to protect the toadlets, set up road barricades and distribute brochures about the migration, Levinson said. To volunteer, go to www.toaddetour.com.