The Purpose of Counter Shading on Frogs

Frogs are amphibians and live part of their life in water and part of their life on land.  They are coldblooded animals, and therefore their body temperature is the same as the temperature of their surroundings.  Frogs need water, but they do not need to drink water.  Rather, they absorb it through their skin.  Frogs have strong hind legs for jumping and sticky tongues for catching insects.

Another interesting characteristic about frogs is their coloring.  On their skin, they have a color pattern known as counter shading.  Because of this counter shading, the frog is very light on the underside and much darker on the upper part of its body.  The counter shading provides camouflage for the frog and keeps the prey from being able to see it easily.  Whether the prey is looking at it from the top, bottom, or even from the side, the prey cannot see it very well because the counter shading makes the frog very hard to distinguish from the things around it. 

Sunlight shining on the top of the frog’s body casts a shadow on its underside, thus making it appear to blend in with its surroundings.  When a frog is in the water, and a predator views it from the bottom, it will have a hard time seeing the frog against the bright sky.  Also, a predator viewing it from the top against the dark water will have a hard time distinguishing the frog from the other things around it.

Some frogs have patterns of spots, stripes, or uneven patches.  These patterns help it to hide from predators in places like leaves or the forest or the bottom of a pond.  One type of frog, called the spring peeper, has an X mark on its back.  This X causes it to be almost invisible when it is on the ground or perched on a blade of grass.

Some frogs are able to change the color of their skin to match the surfaces near them.  Also, there are other frogs which have very bright coloring.  This may not help the frog look invisible, but it signals to the predators that the frog is poisonous.  It may be truly poisonous, or it may simply be mimicking a poisonous look-alike.

Although it may seem to humans that the many color variations on a frog make it stand out even more, this is not the case for other animals.  To the predator, the frog seems only to be part of a broader pattern of that which surrounds it.