The Strange Lives of Wood Frogs

Nature is out of its damn mind. To prove this, one need look no further than the frozen frogsicles that make up a surprisingly large proportion of the amphibian biomass of the mid-Atlantic. These are Wood Frogs, which have adapted to North American winters by freezing nearly solid.

When the temperature drops, a Wood Frog produces just enough of a kind of natural glucose based anti-freeze to protect the interior of its cells from damage while the rest of its body shuts down and turns into a chunk of ice. Then, when the weather warms up again, the frog unfreezes, none the worse for wear, and happily goes about its business. This makes the species one of the hardiest of all frogs, with a range extending far above the Arctic Circle, where they can spend up to eight months of the year in a state of suspended animation.

While the frogs are well-studied, there is still much about their life cycle which remains a mystery. In particular, scientists don’t understand how the frogs are able to restart their hearts after months of total inactivity.

Where I live in the northern part of the great state of Delaware, Wood Frogs are very common, yet rarely seen. Most years they’re the first amphibian one hears out in the woods, weeks before the Spring Peepers and months before the Bull Frogs. Yet, one has to know exactly where to look to clap eyes on one. They seem to be very picky about the pools they choose to mate in, though once they’ve settled on their ideal vernal sump, they really go at it.

Completely by accident, I discovered one such optimal breeding pond last year while out for a run in Iron Hill Park, a New Castle County park in Newark Delaware which borders I-95 (if you’ve ever driven between New York and Washington D.C., you’ve probably gone right past the spot while chuckling derisively at the fact that Delaware takes about ten minutes to drive across).

Starting in the colonial era and lasting up until the early 20th century, Iron Hill was the site of extensive open-pit iron mining. The mines have long since been abandoned, but the pits remain, and several have semi-permanent bodies of water at the bottom of them.

One such vernal pool in an abandoned pit mine is located near the parking lot. But while this pool is usually squirming with Bull Frogs later in the year, it’s curiously lacking in Wood Frogs in the late winter. However, an otherwise similar pond which turns more Wood Frog than water is located down several unmarked trails, deep in the woods in a part of Iron Hill Park that sees few visitors. Why the Wood Frogs love the one pond and avoid the other is just another one of those frozen frog mysteries.

Where I live, the wood frogs only breed for a few unseasonably warm days in late winter. By the end of March they’re through, and I personally don’t remember ever seeing one at any other time of the year…though they must be around.

A few weeks back, I took my nephew Oliver and my neice Indigo out to see the Wood Frogs. The kids spent quite a while trying to get their hands on one, but though the frogs were recently defrosted, they were quite nimble.

The video above gives you some idea of how loud the Wood Frogs get when they’re mating. I guess they have to be, since they’ve only got a few days, or even hours, to do what needs to be done before the temperature drops again and they all freeze. This was back at the end of February. We’ve had numerous days well below freezing since then.

By the way, that’s my nephew Oliver in the background saying “I really want to jump in the water.” He was determined to catch a few Wood Frogs, though I suspect if he actually jumped in the freezing mucky water full of thousands of slimy frogs and hundreds of thousands of even slimier frog eggs, he would soon regret it.

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