Nebraskaland

16 NEBRASKAland • AUGUST-SEPTEMBER 2015 Now You See Me By Dan Fogell When I was really young I thought all frogs were green. Maybe it was all the children's books I had with green frog illustrations, or that the most common frogs where I grew up were actually called "green frogs." Then one day on a camping trip I found a light brown frog with black spots. A little library research told me it was a northern leopard frog. Good name, I thought. How come it had spots? Why wasn't it green? It turns out that many frogs are not green. They can be gray, blue, red, black, yellow or a combination of colors. They can be spotted, striped or have all kinds of strange colored shapes on them. There are even frogs that can change their skin color throughout the day, or even in just a few minutes. Why, you ask? What kind of survival strategy do frogs have invested in their skin color? Green is easy. It's the color of the vegetation in the ponds where frogs often live – including lily pads, duckweed, even the algae that grows on the water surface – so there is an obvious camouflage advantage. But not all frogs live in ponds. Some live in mud along the shore. Some live in grass near the water. Some live in trees. And each of these species has a skin color and pattern that affords it an amazing camouflage. Even the light brown, spotted skin of leopard frogs makes them difficult to find in grass along the water's edge. Here in Nebraska, having light brown skin with stripes or spots provides excellent camouflage in grass, which is a common habitat feature alongside ponds, lakes and streams. Our treefrogs here have the special ability to change their color and their pattern when necessary. They're called Cope's gray treefrogs, and they may be gray, green or even white. Sometimes they have a pattern, and sometimes they don't. This versatility in color and pattern is due to physiological changes to cells called chromatophores in the frog's skin. Temperature changes and certain hormones can make these cells either express color or not, thus changing both their color and pattern and making them hard to detect on either leaves, bark or other substrates. But when they jump, treefrogs use a different strategy involving skin color – something known as flash coloration. On the inside of their thighs, treefrogs are very brightly colored – usually yellow or orange, so that when they leap they "flash" their bright colors. This is an advertisement saying "I taste terrible, so don't bother eating me." The bad taste comes from poison glands found throughout the frog's skin. All frogs have poison glands in their skin, but at least treefrogs are nice enough to warn you. Speaking of warnings, camouflage is not always the best strategy. Some tropical frogs don't even try to hide. They are bright yellow, red, fluorescent green and blue. These are the dart frogs or poison arrow frogs of Central and South America. And although all frogs have poison glands, these frogs have especially toxic, even deadly poisons in their skin. In nature, bright colors (called aposematic coloration) often mean "stay away" and these little frogs definitely follow that rule. They don't mind letting you know where they are because they're pretty confident nothing is going to eat them. ■ Dan Fogell is a herpetologist and author of A Field Guide to the Amphibians and Reptiles of Nebraska. Nebraska treefrogs have the special ability to change their color and pattern when necessary. A plains leopard frog hides in grass and mud, camouflaging its entire body. The lack of camouflage of poison dart frogs of Central and South America warns predators to "stay away." PHOTOS BY DAN FOGELL

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