General Curator Jack Cover at Gunpowder Falls State Park

There's a vernal pool next to the Gunpowder River in Baltimore County, Maryland, that National Aquarium General Curator Jack Cover has visited almost every spring for the past 50 years.

His first trip was in 1971, when he was a freshman at Baltimore Polytechnic Institute and a member of the school's herpetology club. He also conducted field research there in 1978 as a student at Towson University, working his way toward a bachelor's degree in biology.

He says that in early spring, the chorus of hundreds of tiny spring peepers—the vernal pool's smallest frog—can be as loud as a jet plane or a rock concert. He visits this and other vernal pools just to hear it.

Listen as Jack Explores

Jack explores a vernal pool in Gunpowder Falls State Park and talks about some of the species found there, as well as the importance of protected habitats.

Importance of Protected Land and Water

Of the many species Jack sees when he visits this spot, none are currently endangered, but their long-term survival hinges on protected bodies of water and forests. State parks like Gunpowder Falls and other protected lands provide critical habitats that support biodiversity.

Many of the vernal pools in the Baltimore area that Jack visited in the 1970s and 80s have been paved over and developed. One of his favorites, off Putty Hill Road in Parkville, was bulldozed in the late 1970s to make way for an apartment complex.

The fact that vernal pools are not connected to other bodies of water and only exist during the wetter months of each year—filling up with rain and snowmelt and drying out in summer's heat—doesn't make them any less important. The still water, fallen leaves, absence of fish predators and abundance of invertebrate prey make them ideal breeding grounds for amphibians like salamanders, frogs and toads, which travel to the pool from up to a mile away each year.

Occasionally, animals from one vernal pool stray to another one nearby, facilitating genetic exchange between populations. This creates what is known as a metapopulation, spatially divided populations that interact with each other.

Metapopulations exist where there is continuous, connected forest habitat, as is found in this and other state parks. Protecting vernal pools in forested corridors is necessary for the long-term survival of many of Maryland's amphibian species—and other wildlife that depend on the continued existence of these unique temporary wetlands.

Vernal Pools' Fauna and Flora

Each spring, warm rains trigger multiple amphibian species to migrate to vernal pools to reproduce, and they typically follow a certain sequence, with wood frogs arriving first and American toads arriving last.

If you visit a vernal pool in Maryland in spring, this one in Gunpowder Falls State Park or any other, you can see a wide variety of animals and plants.

Wood Frogs

Wood frogs are the first species to arrive on the vernal pool scene, often during the first warm rains of late winter, sometimes migrating over patches of snow in February. They spend winters hibernating under the forest's leaf litter. During especially cold winters, this frog can survive brief periods of freezing when even their hearts stop beating; glucose in their blood acts as an anti-freeze that protects their cells from ice damage. Male wood frogs arrive at the vernal pools in large numbers and begin calling to attract females, producing a duck-like clucking call. Females often lay their eggs right next to each other to form large, communal egg masses, which ensure some eggs survive even if the pool dries up or freezes. A single female wood frog lays 1,000 to 3,000 eggs, which are already hatching once other frog species begin to show up at the vernal pool later in the spring.

Spotted Salamanders

Spotted salamanders are one of the four members of the mole salamander family native to Maryland; they're found throughout the state except for a few lower Eastern Shore counties. Spotted salamanders are rarely seen outside of the spring breeding season. They spend much of the year hidden beneath fallen logs and in burrows beneath moist leaf litter. Males migrate from the surrounding forest to vernal pools on warm, rainy nights soon after wood frogs arrive. They are followed by egg-laden females who are courted by males performing what's called a "nuptial dance." Males deposit packets of sperm called spermatophores on the bottom of vernal pools; these are picked up by females to fertilize her eggs. She later deposits two to four egg masses, which are attached to submerged sticks and vegetation. These masses turn milky white and resemble submerged cotton balls.

American Toads

American toads are one of only two species of true toads found in Maryland, and they are typically the last species to arrive at vernal pools for breeding. Males gather in large numbers and produce a long, distinctive, musical trill call. When an egg-laden female arrives at the vernal pool, there is intense competition among the males to grasp her and fertilize her eggs. Females lay 4,000 to 8,000 eggs in gelatinous, string-like strands from April to July. The eggs hatch after three to 12 days, and the tadpoles are nearly black in color. American toads can be found throughout the state of Maryland, in a variety of habitats. They're easily seen and heard during the day, and their calls can be heard on warm, humid nights from March to July.

Eastern Fairy Shrimp

Eastern fairy shrimp are small crustaceans found in Maryland's vernal pools. Adults are about an inch long and are pale pink in color. They feed on algae, detritus and small invertebrates, and are fed upon by salamander larvae. Some Eastern fairy shrimp eggs hatch soon after they're laid when the vernal pools are full of water, but others are able to survive through the pool's dry phase. These eggs remain dormant in the dry soil and then hatch once spring rains and warm temperatures arrive.

Skunk Cabbage

Skunk cabbage is a wetland plant found in the eastern U.S. in forests, woodlands, vernal pools and swamps. It sprouts in early spring, often when snow is still melting, thanks to its ability to produce its own heat through a process called thermogenesis. The temperature within the plant's spathe—which is a deep purple, leaf-like hood—can be 20 degrees warmer than the surrounding air temperature. Inside the spathe, a white, petal-less flower stalk emerges, followed by a whorl of large, fast-growing green leaves, which are often the only green plants in the early spring landscape. To attract pollinators, these plants emit a foul odor (the source of their common name), and the smell is stronger when the plant is damaged. If you step on a skunk cabbage, your nose will know it.

Hear About the Snake on the Bus

Something happened when Jack was a child that sparked his lifelong love for wildlife and their habitats. Listen as he tells the story.

Stay tuned for more stories in our Aquarium Inside Out series!