What is the most common animal found in Pennsylvania's forests?
You might think it is a mammal such as the white-tailed deer or perhaps a songbird such as a sparrow. However, the most common animal in Pennsylvania's forests is not a mammal or a bird at all; it is one of the Commonwealth's 39 frogs and salamanders, which means that it is an amphibian. Many people think amphibians are animals that live in the water for part of their lives and then on land during the other part, but this is not always true. Some amphibians never enter the water. Others lay their eggs on land under rocks or logs instead of in ponds. One thing amphibians all have in common is that they go through different life stages, with different body forms, as they mature ("metamorphosis"). This makes them unique in many ways and sometimes hard to identify.
In Pennsylvania, the life cycle of a frog has four stages. (1&2) Adults mate and lay eggs in water. (3) The eggs hatch into free-swimming tadpoles. most tadpoles scrape algae from the bottom of the pond with a special "beak." (4) The tadpole matures into a metamorph, or froglet. The tail provides energy to the metamorph as it emerges onto land and develops adult mouthparts. The metamorph cannot eat until the change is complete! Illustration by: J.B. Grant.
Eggs in Water. Photo Credit: Robert Hill
Amphibian eggs can be laid in the water (top) or on land in moist environments (bottom). All frogs and some salamanders in Pennsylvania lay their eggs in water. Salamanders that lay their eggs on land often guard them from predators, like this red-backed salamander. Photo Credit: Michael F. Benard, www.mister-toad.com.
Amphibians are Vertebrates
Amphibians are animals that have backbones, like humans do. But how else are amphibians similar to and different from humans and other animals? Look at your skin. Is it wet or dry? Is it hairy or smooth? Amphibian skin does not grow hair, feathers, or scales. Even the "warts" of a toad are each smooth to the touch. Amphibian skin is moist and smooth, which lets it pass water and oxygen better than human skin does. Amphibians never drink with their mouths. They absorb water through their skin. Some amphibians even have a visible patch of skin on their belly through which they get their water.
What is the difference between a frog and a toad?
A toad is a kind of frog. Frogs and toads both belong to the same group of animals, the order Anura. "Anura" means without a tail. There are dozens of frog families within the group Anura! We only have four frog families in Pennsylvania. So, when we think of frogs, we are usually thinking of frogs in the family Ranidae (the true frogs, or ranids). North American ranid frogs are good jumpers with long legs, webbed hind feet, and smooth skin.
Bullfrog. Photo Credit: Brad Wilson, DVM
When we think of toads, we are usually thinking of frogs in the family Bufonidae (the true toads, or bufonids). True toads have stout bodies, short legs, and bumpy skin. They are not the greatest swimmers. Handling toads does not cause warts. The bumps on their skin are not warts, but groups of poison glands. In Pennsylvania true frogs spend more time in or near water than the true toads. Visit a local pond after sunset during the spring breeding season (March through May) and you will see what great swimmers the true frogs are.
Many amphibians are so good at breathing through their skin that they do not need lungs. In fact, 15 of Pennsylvania's 22 living salamander species have no lungs at all. Instead of inhaling, these lungless salamanders use the "lung" muscles to shoot their tongues like slingshots. A fast tongue lets the salamander catch more insects than a slow one. The diet of amphibians varies greatly by species and life stage. Most are carnivorous at some stage in their lives; others have an herbivorous stage.
Many salamanders are so good at breathing through their skin that they do not have lungs. Lungless salamanders are much smaller than salamanders with lungs. Does the spotted salamander in the top photo look bigger than the others? The spotted salamander has lungs, while the rest belong to the family of lungless salamanders.
Spotted salamander. Photo Credit: Michael F. Benard, www.mister-toad.com
Northern slimy salamander. Photo Credit: Michael F. Benard, www.mister-toad.com
Long-tailed salamander. Photo Credit: Brad Wilson, DVM
Green salamander. Photo Credit: Michael F. Benard, www.mister-toad.com
Protection from Predators
Although they are small, many salamanders possess defensive weapons other than teeth. The smooth skin of amphibians is full of glands. One type, the mucous gland, keeps the skin moist. In some amphibians mucous glands produce extra-sticky slime. The slime of a slimy salamander is sticky enough to temporarily glue a hungry snake's mouth shut. It might also cause your fingers to stick together if you handle the salamander roughly. Salamanders should never be handled if you have used your hands to apply insect repellent or sunscreen. The same skin that allows them to breathe and drink can also allow chemicals that can harm them to pass through.
Another trick used by lungless salamanders is dropping their tails when they are being attacked. Many lungless salamanders have special blood vessels in the tail. When the tail drops off, the blood vessels self-constrict and prevent the salamander from bleeding to death. The tail then wriggles wildly and turns the predator's attention away from the salamander. Salamanders store fat in their tails. If the predator does not find and eat the dropped tail, the salamander tries to return and eat its own tail.
A twenty-third species of salamander, the tiger salamander, used to be found in Pennsylvania's forests. Tiger salamanders are now considered to be gone, or extirpated, from the Commonwealth. It is not legal to purchase or sell tiger salamanders in Pennsylvania. This rule will help prevent damage to native tiger salamanders, should they be rediscovered in Pennsylvania.
Tiger salamanders belong to a group of salamanders called "mole salamanders." Four out of Pennsylvania's 22 salamander species belong to the mole salamander family. Just like the moles that dig in soil, mole salamanders spend much of their time under ground. Most of the mole salamanders come out of the ground in spring to lay their eggs in woodland pools. Mole salamanders use a second type of skin gland to defend themselves. Their heads and tails contain poison glands that squirt a milky, bitter chemical mix into the mouths and eyes of predators. You should always wash your hands after handling an amphibian. Their defensive chemicals can be very irritating to your eyes, nose, and mouth.
Salamanders are not the only type of amphibian to keep predators away with skin gland secretions. All of Pennsylvania's 14 frogs and toads are covered with mucous and poison glands. The warts on a toad are enlarged poison glands bundled together to form a group. Even smooth-looking frogs may have poison glands. The pickerel frog produces not only a distasteful poison but also an odor. The smell of the pickerel frog warns predators before they bite that its taste will be bad! Pennsylvania is also the home of another bad-smelling ("malodorous") and bad-tasting frog. This frog, the eastern spadefoot toad, smells like garlic when handled.
Eastern spadefoot toads spend the winter below ground. They dig deep enough to escape freezing temperatures. Other frogs rely on a good layer of leaf litter from forest trees to give them shelter. How does a frog in leaf litter resist freezing? It doesn't! Wood frogs and other leaf-litter users freeze solid in the winter. Within 10 minutes of its toe-tips freezing, the wood frog sends sugar all over its body. The sugar slows down the freezing process. A wood frog will freeze solid in about 24 hours if temperatures are right. The sugar also keeps ice crystals from damaging the wood frog's body tissues. Only about a dozen vertebrate animals in the world can freeze solid and survive. Pennsylvania forests are home to four of them! They include spring peepers, gray treefrogs, wood frogs, and chorus frogs.
One amphibian in Pennsylvania that few have seen but most have heard is the northern spring peeper. Though only a little bigger than a quarter, it has a loud, distinctive mating call described as a high-pitched whistle. male peepers sing in choruses in early spring, usually near water, and their vocal sacs look like shiny bubbles. Photo Credit: Michael F. Benard, www.mister-toad.com.
So what is the most common animal in Pennsylvania's forests? It is a lungless salamander, the red-backed salamander. This forest-dwelling salamander is often more abundant than birds or mice. Amphibians are a key part of our forests. In turn, the shade and shelter of our forests are important to amphibians because they rely on cool, moist, and unpolluted environments. When practicing forest management activities such as timber harvests and road building, it is important to protect wetland areas and bodies of water that provide valuable amphibian habitat.
Written by Jacqualine Grant, assistant professor of biology, Southern Utah University, and Sanford S. Smith, extension specialist in forest resources and youth education, Penn State.