Flea Toad May Be World’s Smallest Vertebrate

A trio of biologists from the Universidade Estadual de Santa Cruz, Brazil, verified that a small frog, Brachycephalus pulex, also known as the Brazilian flea toad, found only in southern Brazil , is not only the world’s smallest amphibian, it is also the world’s smallest vertebrate. Their article is published in the journal Zoologica Scripta.

Researchers first discovered the little frog in 2011. The discovery team found evidence that the frog only lives on a few hills in southern Bahia, Brazil. At the time, researchers also thought the frog was a toad, hence its name.

For this new study, researchers ventured to the site where the original specimens were found, captured and released several more after measuring them and checking for signs of maturity. They wanted to make sure those they were measuring were adults. To do this, they had to check both their gonads and their vocal slits. Once they confirmed a specimen was as big as it could be, they measured its body length.

Measurements of 46 specimens revealed that the average body length of the men was just over 7 millimeters, making them smaller than a pea, or in other words, two of them could rest comfortably on a little nail. Females were on average 1 millimeter longer. The researchers noted that the smallest specimen found was just 6.45 millimeters long, which they say is about 30% smaller than the smallest frog previously observed.

The discovery represents the smallest vertebrate observed, but not the smallest possible. They suggest there might be smaller creatures that have yet to be found and studied. They also note that there are likely limitations—most small frogs have quirks, they point out, such as fewer toes than other frogs or insufficiently formed ears—signs that suggest smaller frogs might have hard to survive.

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