Wood Frog

The amazing North American wood frog has the curious ability to withstand freezing throughout the winter.

Wood Frog
Frozen wood frog from David Attenborough's Natural Curiosities © ‎Tim Shepherd

Frozen wood frog from David Attenborough's Natural Curiosities © ‎Tim Shepherd

Classification

Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Anura
Family: Ranidae
Species: Lithobates sylvaticus

Overview

Found throughout northern North America the diurnal, day-living, wood frog is an amphibian famous for its remarkable adaptation to withstanding sub-zero conditions.

Wood frogs reach just over 7cm in length and just under 8g, with females tending to be larger than males. They have a dark mark over their eye and overall colour can vary between brown and rust.

Wood frog on forest floor

Wood frog on forest floor

Diet

As tadpoles, wood frogs eat a variety of plant detritus and algae. They are also known to eat eggs of other amphibians, including fellow wood frogs, if they are in abundance.

Adult wood frogs make use of their forest habitat by eating forest-floor dwelling invertebrates. Movement of prey triggers a lunge, throwing the sticky tongue out towards the prey to be dragged back into a wide mouth. This reflex is so strong that frogs can even mistake inanimate objects for prey if they move suddenly.

Attenborough on Wood Frogs

Habitat

Spending the summer and spring months in temporary pools and boggy areas, wood frogs migrate to upland areas to find loose leaf litter or soil to hibernate in.

A complex relationship with their habitat means that they may be subject to future threats with any habitat loss.

Freezing

Any small animal living in areas subject to very cold winters faces a tough winter, especially those that are endothermic like amphibian wood frogs.

Wood frogs are then able to tolerate the freezing of their body tissues during hibernation when the temperature drops below zero. They can stay in this state for weeks on end, waiting for the sun to come out.

By collecting urea, the molecule that makes up urine, in their tissues and converting glycogen in the liver into glucose they are able to inhibit the formation of ice crystals, essential to prevent the rupture and irreparable damage of cells.

Find Out More

Experiments on multiple freeze-thaws of wood frogs has led some to think the process may help to keep human organs undamaged during the transplant process.

Quick Facts

  • State amphibian of New York.
  • During mating in the Spring, male wood frogs sound like ducks quacking.
  • Tadpoles may cannibalise other wood frog eggs!
  • Known predators include herons and snakes.