The scientists then applied the frog fluids to the tails of mice and placed the rodents in cages with colonies of biting mosquitoes.
Mice treated with the frog-skin formula received only a few bites during the first hour of the experiment. Those that received a control treatment of water were almost always bitten in less than 15 minutes.
But mice with tails covered in a deet-based solution avoided bites for up to two hours. (Related feature: Bug repellents tested in the Florida Everglades.)
Williams says the frog extract may have potential to be used as part of a deet-free insect repellent for people who have adverse reactions to the chemical or don't want to expose themselves to it.
Stephen Regenold, a Minnesota outdoor enthusiast who often blogs about his product finds, is intrigued by the possibility.
"I have a friend whose wife is seven months pregnant, and I'd be wary of recommending she put chemicals like deet on her skin," he said.
"Researching natural forms of repellent could be helpful for a lot of people."
But human tests for a frog skin-based repellent haven't been carried out, and Williams and his team already foreseeor foresmellsome obstacles to making a commercial product.
"We tried putting some of the chemicals from frog skin in a lotion," he said, "but the odor was too strong."
Some of the frogs' secretions smell of rotting meat, the team reports. Others give off aromas of nuts or thyme leaves.
The researchers say the strong smell is what repels biting insects.
Brian Weekley is president of the Minnesota-based repellent company Bugg Products.
He notes that just because a compound is natural, that doesn't mean it will be practical for people to wear or for companies to manufacture.
"Every natural compound needs to be tested in humans for safety and efficacy, and the government approval process can cost over [U.S.] $300,000," he said.
"We'll have to wait for more scientific results to see how promising this repellent is."
For now, the University of Adelaide's Williams isn't putting much store in commercial ambitionshe's more focused on finding out what other properties of frog secretions might be useful to humans.
"We need to identify more of the chemicals liberated by frogs and relate them to real-life functions, like mosquito repelling, antipredator cues, and sexual cues," he said.
"There's a lot we don't know about frog chemical ecology."
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES