Here’s an eastern spadefoot, a medium-sized frog that is relatively common but rarely seen unless you happen to be trapping amphibians around an ephemeral pond. They’re burrowers, so they need loose, sandy soil that’s easy to dig into. They dig with their hind feet, backwards.
The adults are rarely seen in daylight. They usually only come out of their burrows at night to catch bugs, earthworms, and slugs. But you can sometimes find hundreds of tiny recently-metamorphosed spadefoots leaving a pond during the day.
The easiest way to tell them from true toads (the Bufo genus — around here that would be the Fowler’s toad and the American toad) is their eyes — their pupils are vertical instead of round. They also have two curved yellow streaks on their backs.
Also, they try to curl up into a ball when threatened. I’m not sure what threat would be deterred by this — definitely not a human — but it is adorable.
In the comments for last week’s cricket frog post, I mentioned that the cricket frog was not the smallest frog in Florida. Then, I completely neglected to say what the smallest frog was. So, here it is: the little grass frog. It’s related to the spring peeper, in the Pseudacris genus.
They are tiny. The frog pictured above is sitting on my raincoat, which doesn’t really give a good sense of scale. Here’s one on a square of ordinary velcro, and one on the palm of my hand:
Little grass frog, on velcro.
Little grass frog, on hand.
The little grass frog is another amphibian that breeds in ephemeral ponds, as well as other grassy-edged bodies of water. I’ve only ever seen two, and I spent a great deal of time in their habitat.
It’s not particularly rare; it’s just very hard to see. Put this little guy in some dead grass, and he would disappear. These, like literally hundreds of mole salamanders, ornate chorus frogs, and leopard frogs, were captured in an attempt to catch flatwoods salamanders (more about those next week). I’ve never seen one just hopping around on the ground. If you do, what luck! Take a picture. Preferably with an object for scale, because nobody will comprehend just how tiny it is without one.
Go to a pond in the southeast and walk along the muddy edge, and you’ll likely see tiny frogs leaping into the water ahead of you. You’ll rarely see the frog beforehand; the first hint of its existence will be a little splash. They launch themselves many times their body length, springing from the weeds into the water as if assisted by wings. From the opposite side of the pond, you’ll hear repeated clicks, like stones being struck together.
If you can find one sitting still long enough to get a good look, you’ll see that it’s about an inch long: a slender, long-legged creature, with bumpy skin and a triangle on the back of its head. It will be some combination of brown, black, green, and gold.
There are two species of cricket frogs: northern and southern. The northern species has slightly longer legs and a slightly more rounded snout, but they are otherwise very similar. They sometimes interbreed where their ranges overlap. (Those shown in this post are the southern species or hybrids of the two.) Between the two species, they cover most of the eastern half of the US.
The breeding season depends on the local climate; in Florida they may breed year-round, while in the northern edge of their range it’s limited to spring. Adults eat insects and spiders, while the tadpoles are vegetarians and feed on algae. The tadpoles are actually longer than the adults, if you include their tails, which are long, transparent, and often black-tipped. The black tip may be useful in confusing predators into grabbing for the tail instead of the body. This is good, because cricket frog tadpoles are eaten by just about everything else in the water — dragonfly larvae, salamanders, fish, snakes, other frogs… The lucky tadpoles which survive can take anywhere from 4 to 12 weeks to metamorphose into adults.
Some animals live their lives on a strict annual timetable. Migratory birds set off about the same time each year. Hibernating animals start stuffing themselves and building up insulation-fat at the same time. Many species have reproductive cycles that match the seasons.
Some are so predictable and noticeable that they can come to symbolize a season. When the sandhill cranes arrive at the lake near my parents’ house, it is fall. When I lived there, in northern Florida, the sight of a swallow-tailed kite drifting gracefully through the sky meant summer was arriving. I have always liked summer, even in Florida where many hate it, so a glimpse of a kite always made me smile, and not just because they are beautiful. Which they certainly are. I don’t have a good photo of one in flight, so here’s a video:
But long before I lived in Florida, I lived in a much colder place: northwestern Pennsylvania. That area gets a lot of snow, and while they’re used to it, everyone is pretty sick of it by March. The earliest signs of spring are important. Spring there is announced by two sounds: the calls of Canada geese flying north, and the deafening chorus of spring peepers from every creek and roadside ditch that isn’t frozen.
Last month, in a post about the green anole, I mentioned that it was able to change color. Anoles and chameleons are not the only color-changing animals. If you’ve ever caught a frog outdoors in cold weather and it seemed to get lighter as it warmed up in your hands, that wasn’t your imagination.
Backyard Biology has a fantastic explanation of frog skin colors and how they can change.
The ever-changeable, Gray Treefrog. How does it do it?
Green is a popular color for frogs, and birds too, but that lovely green color doesn’t come from a green pigment as you might expect, but from the interaction of multiple layers of specialized color and light-reflecting cells in the upper layers of their skin.
Frogs have three layers of chromatophores (color-producing cells) in their skin. The deepest layer are melanophores that produce melanin pigment giving skin a brown to black color. The middle layer are iridiphores which contain no pigment but instead have mirror like plates capable of producing iridescence, or when viewed from a certain angle, reflect blue light. The most superficial layer of chromatophores are xanthophores that contain a yellow pigment. When the middle layer of iridophores interact with the top layer of yellow-pigment containing xanthophores, you get what elementary school students have learned: yellow paint + blue paint…
Last week I talked about mole salamanders and the ponds they live in. It’s not just mole salamanders using those ponds, though! Today, I thought the ponds themselves needed a post. Mole salamanders, and many other amphibians, tend to breed in what are known as ephemeral ponds, or vernal pools. Whatever you call them, they are just low spots that fill with water at certain times of year, but their temporary nature is what defines them, and what makes them an essential wildlife habitat.
Even though the rainiest season in most of the South is summer, the ponds usually hold water in winter, after the late fall rains. There may be more rain in summer, but it is promptly sucked up by tree roots or evaporated in the heat. In winter, the trees are dormant and the air is cooler, so water is left to saturate the ground and pool in the hollows.
How long the ponds will hold water is an important factor for wildlife. Some of the shallow pools dry in a matter of days. Others have at least a puddle at the deepest point for most of the year. In drought years, almost none of them will have any water at all. Continue reading Ephemeral Ponds