Nature News: The miracle of wood frog, spotted salamander egg cases

Back in March, something wonderful happened. When nighttime temperatures hit the low 40’, when it was rainy and drizzly, huge numbers of amphibians began to move about, heading toward ponds to mate and lay eggs, most often to the vernal pools (temporary, fishless ponds) where they were hatched.

The two amphibians that partake of this annual early spring-late winter migration are wood frogs and spotted salamanders.

Wood frogs belong to a group of animals that have the remarkable ability to freeze but not die. To hibernate, they bury themselves in the ground and go into a deep hibernation in which their hearts stop beating, they stop breathing and partially freeze. Then with warm (above 40 degrees F) spring rains they revive, dig themselves out of the ground and head to the water to mate.

Spotted salamanders don’t carry things this far, but they do hibernate in underground burrows and tunnels, also emerging in the spring.

So, this magical thing happened (referred to as “Big Night” by wood frog and spotted salamander aficionados). These hardy amphibians came out of hibernation and headed to their ancestral pools to reproduce. Once they finished mating and laying eggs, they headed back to the woods to lead a very terrestrial existence for the rest of the year. Now, what remains in those pools are their egg masses.

So, now is a good time to check out your local vernal pools to see if you can find frog and salamander egg masses. The egg masses are big and have characteristic features that make it relatively easy to distinguish wood frog from spotted salamander eggs. Almost always the eggs are laid in vernal pools because, due to their temporary nature (vernal pools dry out in late summer and early fall), they are fishless. Fish would love to chow down on those huge egg masses. They are so easy to see.

Once you know what to look for, it is relatively easy to tell a spotted salamander egg mass from a wood frog egg mass; spotted salamander egg masses are surrounded by a jelly coat, wood frog egg masses are not.

If you were to pick up a spotted salamander egg mass (which you really shouldn’t), it would hold together and you would see that in addition to the gel surrounding each egg, there was a thick gel surrounding the entire mass.

If you were to pick up a wood frog egg mass (which you really shouldn’t), it would be looser and would fall apart more easily. The surface would look like a cluster of grapes. Each individual egg has its own gel-coat, but the entire mass lacks the extra protection of that outer layer.

Both wood frogs and spotted salamanders attach their eggs to vegetation (though sometimes spotted salamander eggs will rest on the bottom). Wood frog egg masses tend to be attached to overhanging vegetation or to twigs at the surface, whereas spotted salamander egg masses are attached to deeper branches, below the surface of the water. One interesting variation you might see with spotted salamander egg masses. Some have a clear gel-coat while the gel-coat of others is milky-white. The significance of this difference is unclear, but some research suggests it might confer some protection from predation.

Both wood frogs and spotted salamanders are considered to be obligate breeders in vernal pools, meaning they rely upon vernal pools for reproduction. The Seacoast area has an extremely high density of vernal pools, a habitat type threatened by suburban sprawl. If you know of a vernal pool in your area, try to protect it. These little amphibians have been using these pools long before we were here. They are also extremely important members of our forest ecosystems. They are food for an enormous number of predators - snakes, herons, raccoons, skunks and mink, to name a few.

To me, their migration to vernal pools to lay eggs is one of the most lovely of our signs of spring and each year. I seek those eggs out as a reminder of all the mysterious goings-on in my backyard.

Susan Pike, a researcher and an environmental sciences and biology teacher at St. Thomas Aquinas High School, welcomes your ideas for future column topics. She may be reached at spike3116@gmail.com. Read more of her Nature News columns online at Seacoastonline.com and pikes-hikes.com, and follow her on Instagram @pikeshikes.