Glow sticks help Penn State scientists catch frogs

Frogs and other amphibians are in decline in many places around the world, due to such factors as climate change, habitat loss, and disease, so scientists are more intent than ever on counting the ones that remain. But the little critters can be elusive.

This week, Pennsylvania State University researchers said they had found a great way to lure the animals: glow sticks.

Over two weeks in the spring of 2015, the group placed dozens of the light-emitting devices in "funnel traps" on state game lands near the university's main campus in State College. The greenish, six-inch light sticks were similar to what a trick-or-treater might wear around the neck on Halloween.

Traps equipped with glow sticks attracted several times the numbers of creatures that were caught in unlit traps, the scientists reported in the journal Herpetological Review. The species that seemed to respond the most was the eastern red-spotted newt, with lit traps catching six times as many females and three times as many males as there were in the unlit traps.

But the glow sticks also held a significant attraction for three other species that were counted: the spotted salamander, the Jefferson's salamander, and the wood frog.

The reason the lights work so well is not entirely clear. Previous studies have found glow sticks attract amphibians in their younger, larval stages because the lights also invite smaller creatures that they like to eat. But the Penn State study was focused on adults during breeding season, when feeding is not the main item on the agenda.

"I don't know that we actually really understand why, but for some reason they're attracted to the glow sticks," said David Miller, an assistant professor of wildlife population ecology at Penn State's College of Agricultural Sciences.

He was joined on the study by Michael Antonishak, who was an undergraduate at the time of the trapping, and David Muñoz, a doctoral student in ecology. The trio caught nearly 5,000 amphibians in the traps, tagged and photographed them, then set them loose.

The traps were placed in "vernal" pools — rain-fed bodies of water that form during the springtime and dry out later in the year.

The four species that the scientists measured are not in any immediate risk in Pennsylvania, but it is important to count them nonetheless. Without baseline numbers for the creatures, researchers would not be able to tell if their populations rose or fell in the future.

And now that the glow-stick concept has been successfully demonstrated, the authors are hopeful it will prove useful for sampling many varieties of amphibians, including those that are in decline.