Salutations, BugFans,
No, The BugLady did not take a wrong turn at the phylogenetic tree, and no, she hasn’t run out of bugs to write about yet. She’s been out taking pictures for the past six weeks, mostly in wetlands. Since Easter, the sound track has been one of spring peepers and wood frogs (and now leopard frogs and American toads).
So, here’s the deal—if you want to celebrate spring, take yourself to a wetland. The world wakes up early there, particularly in the form of non-flowering plants, many of which put on a grand reproductive push—a promise—long before the flowering plants flower and trees leaf out.
The chant of frogs consecrates spring as surely as do the songs of birds. Wood frogs, along with peepers, chorus frogs, and then leopard frogs breed first—indeed, there was ice at the back of the ephemeral pond when the BugLady heard her first wood frogs on (appropriately) Easter Sunday. Tree frogs and American toads, the next singers, prefer water temperatures about 10 degrees warmer, and the final chorus is sung by green and bull frogs, dwellers of permanent ponds who like their water tepid.
Somewhere, the BugLady heard a character say “We don’t need no stinkin’ backbones,” and that’s been the unofficial BOTW motto. But—it’s her blog/blast/pulpit/party/whatever this is, and it’s time for some uncharted territory. She wrote this for a recent BogHaunter, the newsletter of the Friends of the Cedarburg Bog (which you should all join).
Wood Frog Chorus
There’s something primal about standing at the edge of a pool when wood frogs are breeding. It’s an all-out, (almost) no-holds-barred event.
Along with the far-more numerous spring peepers (whose chorus can be a religious experience), wood frogs (Lithobates sylvaticus) are among the Bog’s earliest singers, often starting their courtship when ice still edges the ponds. Their calls have been compared to quacking, barking, or chuckling.
Frogs vocalize by grabbing a lungful of air and then closing both mouth and nostrils. They force air out of their lungs, through their throat, and into a stretchy pouch of skin under their chin called a vocal sac (leopard and wood frogs have two vocal sacs). Air passing over vocal cords causes them to vibrate, producing sound. In the process, the vocal sac puffs up like a big bubblegum bubble—a natural-born resonating chamber. The air in the vocal sac can be “reused” by deflating the vocal sacs and pushing the air back into the lungs, producing more sound on its way back in.
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Wood frogs are terrestrial, spending their summers on the forest floor and hibernating in winter under soil, leaf litter or logs. They freeze, their cells protected from the formation of internal ice crystals by a bath of glucose and urea (https://www.units.miamioh.edu/cryolab/projects/flv/frogthawinghigh.html).
Naturenorth.com tells us that “Their soft, water-permeable skin is no barrier to ice and so, whenever frost penetrates into their winter home, they freeze. Ice penetrates through all of the fluid compartments of the animal and within just a few hours a mass of ice fills the abdominal cavity encasing all the internal organs. Large flat ice crystals run between the layers of skin and muscle, and the eyes turn white because the lens freezes. Their blood stops flowing and as much as 65% of the frog’s total body water is converted to ice. Breathing, heart beat, and muscle movements all stop and the frozen “frog-sicle” exists in a virtual state of suspended animation until it thaws, see Frozen Alive!.
Jump-started by warming weather (no-one knows exactly how), they thaw from the inside-out and then travel to a pond to breed. What’s all the racket about? Frogs that live and hibernate in the water tend to have softer calls because their audience is already there; wood frogs, peepers, and other terrestrial frogs call loudly, summoning females from woodlands to water (seven of the 19 species of amphibians in Wisconsin are salamanders, but they go about their business silently).
It’s called “explosive breeding”—everybody into the pool! Spring peepers, and later, tree frogs, are marathoners, calling for six weeks and more; but wood frogs sprint—they start, peak, and grow silent in a stretch of about two weeks before leaving the water and resuming their solitary lives on land. It’s a huge expenditure of energy at a time of year when frog food is scarce—wood frog breeding is fueled by fat stored during the previous fall.
No holds barred? In some frog species, females select among the available males. In the chaos of a pond in late April, there’s little time to choose. Female wood frogs are larger than males, and males instinctively grab the biggest frogs they can find (more size = more eggs). She looks for older (older = more fit/fertile) males. A frog’s close-up vision is poor; if he grabs a thin (and therefore “eggless”) female, he will release her; but if he mistakenly clasps another male, a “back off” vocalization from the “grab-ee” quickly informs him of his mistake (apparently, some holds are barred).
Frog eggs don’t have a tough shell, so they must be protected from drying out. Wood frogs prefer to lay their eggs in the fish-free water of ephemeral/seasonal ponds. They breed early and quickly in order to give their tadpoles a chance to mature before the pond dries up.
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A wood frog’s cluster of 1,000 to 3,000 eggs is surrounded by a gelatinous substance and may be attached to vegetation or free-floating. After a short while, green algae grow in the gelatin and provide camouflage. Several females may lay eggs in a big mass, and the large, dark raft of eggs acts as an effective solar collector, causing the temperature in its center to increase by several degrees. Because hatching time depends on water temperature, eggs in the middle have an advantage. Wood frog tadpoles are said to be able to recognize their siblings and to prefer congregating with them.
Wood frogs eat and are eaten by a large number of organisms. Adults feed on small invertebrates like insects, spiders, slugs, caterpillars, and worms; snakes, herons, raccoons, skunks, and mink prey on adults. Tadpoles feed on algae and decaying organic matter (and sometimes, on amphibian eggs) and are eaten by predaceous diving beetles, water bugs, and salamander larvae. Tadpoles develop poison glands as they age, but the skin secretions of adults discourage a single predator—shrews.
Wood frogs occupy a wedge of North America from Alaska to Nova Scotia to the southern Appalachians. Their range extends into the Arctic Circle, farther north than any other frog. They come in a variety of browns, bronzes, and tans; they have a white line on their upper “lip” and most sport a black mask through their eyes.
To hear frog calls, see Wisconsin’s DNR – EEK! Know Your Frogs, and the USGS -Frog and Toad Calls.
The BugLady