Gray Treefrogs’ Self-cleaning Toe Pads
Scientists have discovered that the angle of the toe pads and a secretion of mucus are involved in a treefrog’s ability to stick to wet, smooth leaves, rough, dry trees and other surfaces. They also allow the toes to “self-clean.”
To make their feet sticky treefrogs secrete mucus. They increase their adhesion by moving their feet against the surface of what they are clinging to in order to create friction. As a frog moves across a surface, its feet accumulate dirt, which impedes its ability to stick to the surface it’s walking on. Scientists have discovered that the mucus combined with this friction-creating movement not only allows the frog to adhere to the surface but simultaneously rids their feet of accumulated dirt and debris as they walk.
This remarkable adaptation may provide a design for self-cleaning sticky surfaces, which could be useful for a wide range of products, especially in contaminating environments such as medical bandages and long-lasting adhesives. (Thanks to Janice Perry for photo opportunity.)
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An Unexpectedly Early Juvenile Gray Treefrog
At this time of year the bird-like courtship trills of male Gray Treefrogs can be heard throughout the night from shrubbery bordering wetlands. Mating is taking place, eggs are being laid and typically the offspring would be seen in July and August.
Imagine my surprise when I discovered this 3/4″ juvenile Gray Treefrog recently. It’s possible that it could be this year’s — eggs take 2-5 days to hatch and tadpoles metamorphose into adults in 30-60 days. Early-emerging treefrogs could have parented this individual. But it’s also possible that it could have overwintered as a juvenile. While we’ll never know its exact age, it’s fun to see a juvenile this early in the season.
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Gray Treefrogs Metamorphosing
Gray Treefrogs are often heard but rarely seen, due both to their cryptic coloration as well as the fact that they are arboreal. They tend to perch (grasping trees with their toes which bear large, adhesive, mucous-secreting disks at their tips) in vegetation surrounding swamps and ponds, where their robust, territorial and mating trilling can be heard (males call between 500-15,000 times per hour). To hear trilling Gray Treefrogs go to https://www.youtube.com/watch?v=CSkhM24Fi-k.
After choosing a mate and mating, Gray Treefrog females lay up to 2,000 eggs which hatch in 2-5 days. For the next month or two the tadpoles breath with gills and consume vegetation. Full-sized tadpoles are green or black with red or orange tails. Towards the end of summer, the tadpoles begin their transformation into frogs, developing limbs and lungs, absorbing their tails and changing from a diet of plants to one of insects.
Adult Gray Treefrogs are mottled gray or green (depending on their surroundings, temperature, and humidity) and have an uncanny resemblance to lichen. Recently-metamorphosed young treefrogs such as the one pictured are a brilliant emerald green. (Photo: young Gray Treefrog with adult Gray Treefrog inset) (Thanks to Brian Long for photo op.)
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Juvenile Gray Treefrogs Appearing
Being my favorite species of frog, the Gray Treefrog may get more than its fair share of exposure on the Naturally Curious blog. This amphibian is rarely noticed outside of its June mating season, when the males’ bird-like trills can be heard throughout the night from shrubbery bordering wetlands. Due to its emerald green coloration when young, and its mottled gray/green adult appearance, in addition to its nocturnal habits, this beguiling amphibian escapes detection by most of us throughout the rest of the summer.
However, if you keep an eye out in August, near where you heard those trills in June, you may be successful in spotting a juvenile Gray Treefrog. Having developed legs and lungs, absorbed their gills and tails, and reinvented their digestive system for insects, not plants, they are now permanently terrestrial, except during the breeding season. When a Gray Treefrog is young and newly metamorphosed, it usually remains near the forest floor. As it ages, it may transition to living in the forest canopy. (Photo: juvenile Gray Treefrog; inset – adult Gray Treefrog)
Gray Treefrogs Well Camouflaged
If there is an amphibian that is a master of disguise, it has to be the Gray Treefrog (Hyla versicolor). This remarkable frog is capable of changing its color (gray, green or brown) to match its environment within half an hour, a process called metachrosis. Shades of gray are most common with black blotches on the back while green colors are more prominent during the breeding season and in yearling frogs.
Being a treefrog, it has large, round, sticky toe pads that help it cling to trees and shrubs, where it spends most of its time. Survival is more likely if predators don’t detect you, so Gray Treefrogs have evolved to look a lot like bark.
When the temperature reaches 59° F. the males’ bird-like trilling can be heard coming from foliage next to and hanging over their shallow breeding pools. If you wish to set eyes on a Gray Treefrog, now is the time, as they are calling and a silent Gray Treefrog can be extremely difficult to find!
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Gray Treefrog: A Frog of Many Colors
A Gray Treefrog starts life off as a ¼” yellow tadpole. Eventually it may reach 2 ½” in length, and its body will have turned olive green with a red tail. Upon metamorphosing into a frog, the Gray Treefrog turns a bright emerald green and gradually develops into a mottled greenish-gray adult which can change its color from green to gray in about half an hour to match its environment. The two color phases of the maturing frog (solid green of the young, and mottled gray or green of adult) are so different it’s hard to believe that they are the same species. (Photo: young Gray Treefrog; insert- adult Gray Treefrog)
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Spring Peepers Peeping
The sound of a peeping Spring Peeper in December (yes, this occurred in Vermont this week) conveys to one and all that climate change is not a figment of our imagination. Amphibians are extremely sensitive to small changes in temperature and moisture due to their permeable skin and shell-less eggs. Certain species, including Spring Peepers, Grey Tree Frogs, Wood Frogs, American Bullfrogs and American Toads, are emerging and mating earlier in the year than they did historically. Causal relationships have been found between irregular climate conditions (drought, increasing frequency of dry periods and severe frosts) and decreasing (extinction in some cases) of certain amphibian species.
Behaviorally and physically, warming temperatures are having an impact on amphibians. A recent laboratory study investigated changes in amphibian metamorphosis time due to pond desiccation and whether amphibian immune systems become compromised as a result of these changes. They found that amphibian immune responses became increasingly weaker and white blood cell counts were increasingly lower with higher desiccation. As a result of climate effects, immune systems are weakened, making it more difficult for amphibians to fight off diseases.
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September Snub-Noses
Frogs and toads that hatched from eggs laid this past spring are now two to four months old, and are growing rapidly. Like snakes, frogs and toads shed their skin as they grow — unlike snakes, they eat their skin. Periodically toads and frogs stretch their bodies and then pull their loosened skin off in one piece, much like we pull off a sweater. Using their feet, they then stuff their skin under their tongue and swallow it. When frogs and toads are young and growing fast, they usually shed their skin more often than when they are older and their growth slows down. Not only is their skin a valuable source of nutrients and protein, but if it’s eaten, there is no sign left behind for predators to find.
Most young toads and frogs, with the exception of the Gray Treefrog, look like miniature adults. (Gray Treefrogs are emerald green in their youth, unlike the mottled gray/green adults they will become.) There is one characteristic at this stage that they don’t share with their elders, however, and that is their snub noses. If you’re wondering if the frog or toad you saw is a small adult or a youngster, take a closer look at its nose! If it’s unusually short and blunt, there’s a bit of growing left to do.
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Gray Treefrogs Calling
At this time of year, bird-like trills are often heard in wetlands, where male gray treefrogs (Hyla versicolor) are calling to potential mates. The chorus ramps up at night, but the songsters can be hard to find during the day, when they often hide in tree cavities or high up in the canopy. (Their large toe pads produce mucous which allows them to adhere to smooth bark.) The colors of a gray treefrog vary with the colors of its background and environmental factors such as season and humidity, but shades of gray are most common, with black blotches on the back. Variations of brown, green, and pearl-gray colors have been noted, with green being more prominent during the breeding season. Warm, humid weather seems to elicit calls from these well-camouflaged amphibians. To watch and hear a calling gray treefrog, go to http://www.youtube.com/watch?v=2kd5c4p8-0M. (Thanks to Rachael Cohen for photo op.)
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