Frog

Frogs are among the most familiar animals in the world, present on every continent except Antarctica, and among the most threatened. Their biology is stranger than their ubiquity suggests — some freeze solid in winter and thaw alive in spring, they breathe through their skin as well as their lungs, and the chemistry of frog skin has produced some of the most medically significant compounds ever discovered.

Facts you didn't know

• 1

  Wood frogs freeze solid during winter — their heart stops, their brain activity ceases, and ice crystals form in their tissues. In spring they thaw and resume normal activity. Glucose flood their cells before freezing, acting as antifreeze to prevent lethal ice crystal formation inside cells.

• 2

  Frogs breathe through their skin — cutaneous respiration — supplementing or replacing lung breathing depending on the situation. In cold, well-oxygenated water, some frogs absorb all their oxygen through the skin and don't need to surface to breathe for months.

• 3

  Frog skin is a chemical factory. Hundreds of compounds found in frog skin secretions — including painkillers, antibiotics, and compounds with anti-HIV properties — have been studied by pharmaceutical researchers. Epibatidine, from Ecuadorian poison dart frogs, is 200 times more potent than morphine as a painkiller.

• 4

  Male frogs' calls are individually distinctive — female frogs use call characteristics to assess male quality, and frogs recognize the calls of neighboring males by sound alone.

• 5

  Frogs have no ribs and no diaphragm — they inflate themselves to breathe by swallowing air, using the floor of the mouth as a pump to push air into the lungs.