Color me green!

When I went out to pick raspberries this morning, I found something much more delightful than a bunch of mating Japanese beetles (the scourge of the berry patch!) — a couple of 1-inch Gray Treefrogs hiding in plain sight on the green leaves of the raspberries.

From the side, this little one with its dark facial markings and dark lateral stripe was more obvious.

Although this species is named the Gray Treefrog, because they are quite gray with a dark blotchy pattern sometimes, in bright sunlight on a green background, they are well camouflaged as they match their background. In fact, this frog even matches the particular shade of green of the raspberry leaf on which it rests.

I wonder if they eat Japanese beetles? There are plenty of other insects resting on the raspberry leaves for these little guys to dine on. But these frogs are really only active at night, and usually seek shaded vegetation for their daytime rest.

The color matching camouflage is impressive in both the shade (this photo) and the sun (photo above).

How exactly does a gray treefrog become green?

Looking more like the gray treefrog, I photographed this maxi-sized (2.5-inch) adult in the early morning while it was sitting under an evergreen in the leaf litter.

Frog skin contains a stack of color-producing cells called chromatophores, and many frog species like the Gray Treefrog, have 3 sets of them: a deep layer called melanophores that contain a black/brown pigment called melanin, an intermediate layer called iridophores that lack pigment but contain particles that can reflect blue light, and an upper (most superficial) layer called xanthophores that contain yellow pigment.

Now, it should be more obvious how a Gray Treefrog can transform quickly from its gray color that is produced by the dispersion of deep-lying melanin pigment to a bright green color, produced by the interaction of blue-reflected light from the iridophores passing through the yellow pigment of the xanthiphores (i.e., blue plus yellow equals green to our eyes).

The dispersion of pigment in frog skin is controlled by nerves and hormones, which act on the chromatophores to aggregate (condense) or disperse pigment. Physiologically, in a matter of seconds, when melanophores aggregate their pigment to uncover the iridophores and xanthophores disperse their pigment, a gray frog turns green!

Color changes can even happen while frogs are sitting in the dark in my covered water tank. It just depends on their physiological state, the temperature of their environment, and the amount of hormonal or nerve stimulus they are experiencing.

green on green

Hiding in plain sight by matching the color of your skin to the color of the background is useful for predators stalking their prey or prey trying to escape predation.  It’s also useful in confusing photographers about where to aim their cameras.  Case in point: I saw the bushes moving, wondered if it was a bird, thought it might be a chipmunk, but stared right at the little critter for a full minute before I figured out what it was.

A gray tree frog in green phase hiding in plain sight.  It wasn’t this obvious without the zoom on the camera to help pinpoint its location.

It’s scientific name gives a hint to its ability to change colors: Hyla versicolor. Usually it appears mostly gray with green splotches.

Many species of fish, amphibians, and reptiles have the ability to change color and outward appearance by contracting or expanding the chromatophore (pigment-containing) cells in their skin.  This chameleon-like ability can assist them in better regulating their body temperature, or as suggested, in achieving the kind of camouflage that helps them evade their predators or fool their prey. It is thought that the animals’ eyes perceive the color spectrum of their environment and send neural signals to skin chromatophores to effect the appropriate color changes.

In cases where there doesn’t seem to be a clear message about the color of the background, Gray Treefrogs are often mottled gray and green, or just remain gray, as illustrated below.

Hmm… water in a bird bath? Not sure what color to be.

Gray treefrog sitting on the side of a dish pan, next to green vegetation — again, it’s confusing about what color to be.

Gray treefrog sitting on an orange dahlia — no possibility of a match here.

Green-colored Gray treefrog on the ledge of a wooden door? Clearly a bad match.

Fotogenic Frog

A dahlia flower fell down into some yews, and a shy tree frog decided it was a fine place to rest.

The Eastern Gray Treefrogs are most often found on vegetation, usually high up in the trees, rather than near water, as their name implies.  Actually, I most often see them in the outdoor tank we use to water potted plants.

I picked up the lid of the water tank to see if it needed filling, and found this little guy waiting for me. I don’t know how they get in, and I wonder how they get out.

They are adept at climbing vertical surfaces, even slick ones, using their sticky, enlarged toepads.

Their skin has a warty appearance, like that of toads, and they manage to stay hydrated without taking refuge in pools of water, even during hot days.  Gray Treefrogs tend to hunt at night, often near an outdoor light fixture where they can capture insects coming to the light.

Interesting eye color in this individual, and you notice patches of green in the otherwise gray skin.

Skin color in these frogs is highly variable (hence their scientific name — Hyla versicolor).  Three layers of chromatophores in the skin (color-producing cells) combine to produce the color pattern, which can change (very slowly) from near white to very dark brown, with variations of mottled green and gray in between. Treefrogs don’t match their environment perfectly the way a chameleon does, but their color changes do help camouflage them in their environment somewhat.  More on how this is accomplished in the next post!  Stay tuned.

oops, there are no red-orange pigments in those chromatophores, so color matching this dahlia would be tough.