They are well camouflaged among leaves on the forest floor, and have evolved calls resembling those of insects, making them hard to spot.
"The New Guinea forests are incredibly loud at night; and we were trying to record frog calls in the forest, and we were curious as to what these other sounds were," said research leader Chris Austin from Louisiana State University in Baton Rouge, US.
"So we triangulated to where these calls were coming from, and looked through the leaf litter.
"It was night, these things are incredibly small; so what we did after several frustrating attempts was to grab a whole handful of leaf litter and throw it inside a clear plastic bag.
"When we did so, we saw these incredibly tiny frogs hopping around," he told BBC News.
The frog pictured is sitting on a dime. http://www.bbc.co.uk/news/science-environment-16491477 -via Fark
(Image credit: Rittmeyer et al)