Hunched by the edge of an active vernal pool, adults and youngsters swept the beams of their flashlights over the water’s surface. After a couple minutes of eager anticipation, Frank Dehler pinned the object of his scouring in a column of light. He pointed it out to the others, compelling them to huddle in close, lean over the water and stare.

A spotted salamander swam lethargically near the surface. Perhaps four inches in length from head to tail, the creature’s grayish body was dappled with yellow spots. Disturbed by the unwelcome light, the amphibian swam to the bottom of the pool and burrowed under a carpet of soggy leaves. But another salamander soon appeared, followed by two more. Flashes of their brightly spotted tails lurched in and out of the leaves.

At the far end of the pool, other nature-watchers had made an even more exciting discovery. Dozens of wood frogs, many perched on their own floating egg masses, were busily engaged in propagating the species. Dehler, a volunteer tour guide who lives nearby in York, Maine, said the pool had been even busier when he paid a visit the night before.

“It was a seething mass. The water was just boiling with activity,” he said.

Dehler collaborated with Kenny DeCoster, field trip coordinator with York County Audubon, to guide a nighttime search for breeding salamanders and frogs on Saturday, April 21. A group of approximately 30 curious citizens gathered at the Center for Wildlife in Cape Neddick around 7 p.m., equipped with flashlights and galoshes. As the daylight began to fade, Dehler offered the group some basic facts on vernal pools, describing them as temporary spring pools that reappear in the same location year after year, providing optimal breeding habitat for certain amphibians.

In New England, there are four species that rely exclusively on vernal pools for breeding: wood frogs, spotted salamanders, blue spotted salamanders and fairy shrimp. The fishless waters shelter these animals and their eggs from predation, increasing the success of reproduction.

Dehler has guided vernal pool tours for the last four years, but Saturday marked the first time he hosted a field trip at night, when spotted salamanders are more likely to be seen “congressing.” As for the wood frogs, Dehler had no doubt they would be in a “Dionysian frenzy of reproductive activity.”

The group began walking along Mountain Road but soon stopped at a large vernal pool on the side of the road. The incessant chatter of tiny frogs called spring peepers surrounded the pool and was soon accompanied by the duck-like cackle of wood frogs. The noise swelled to a frenzy as the group patiently waited, with more and more wood frogs pitching in to the chorus. “They’re all fired up,” Dehler said.

Male frogs produce these sounds to advertise their availability to females, Dehler explained. While 70 to 80 percent of the wood frog population in vernal pools consist of males, only about 20 percent of them get lucky. “It’s like a frog singles bar,” DeCoster said.

Dehler described wood frogs as “explosive breeders,” meaning they squeeze all their mating into a short window of time in the spring. The females lay their eggs in fist-sized masses of 500 to 1,000 eggs a few days later, and, if they are not devoured by spotted turtles or other predators, the eggs hatch after about three weeks.

Crossing the road to another vernal pool, guests got their first glimpse of wood frogs. They skittered across the surface of the water and coyly approached one another. Kids excitedly pointed out the creatures to their parents, and flashlight beams leapt from one amphibian couple to another.

Dehler next led the group into the woods along a trail owned by the Kittery Water District. After a quick stop at a vernal pool about a quarter mile into the woods, they turned around and headed farther down the road, reaching their final destination in front of Dehler’s neighbor’s house. The pool located there would prove to be the day’s jackpot, with spotted salamanders swimming at one end and wood frogs breeding at the other.

In the end, the field trip was a mixed success. Although no salamanders were seen in the act of breeding, the wood frogs lived up to Dehler’s promises, and everyone received an education on the importance of vernal pools.

A new Maine law enacted last year established criteria for “significant vernal pools,” based on the number of egg masses they contain. Pools that have been identified as significant enjoy a 250-foot no-touch setback.

“It’s really a significant step forward as far as protecting vernal pools in Maine,” Dehler said.

Although Dehler and DeCoster encourage nature-lovers to observe the wonders of vernal pools, they stress the delicate nature of vernal pool ecosystems. If you find a vernal pool in your backyard, they say, go ahead and take a peek. But be careful not to disturb the busy amphibians.