The Common European Toad
(Bufo bufo), a species that
has a large distribution range
in Europe. Credit: Bert Willaert

They're everywhere! Toads have been able to populate most of the world's continents in the relative blink of an eye. Now scientists have figured out seven factors responsible for the toads' success.

Toads (officially, Bufonidae) originated in the tropics of South America, but fanned out across most of the world over just about 10 million years — a relatively short period of time, evolutionarily speaking. The roughly 500 known toad species are incredibly diverse, both in characteristics and in habitat type and range.

Marc Zimmer uses salamanders like this one, along with mice and fish, to show students that chemistry is cool. Under ultraviolet light, white mice glow green and red and fish go from gray to bright orange and yellow.
Geneticists engineered the animals to have fluorescent proteins in their cells, a harmless process that entertains (and educates) the students in Zimmer's early morning chemistry class at Connecticut College.