AMPHIBIANS

Indicator Species

Seasonal pool indicators are species strongly associated with seasonal pools.  The adults normally breed in seasonal pools and their offspring have higher survival rates in this habitat.

Three species of mole salamanders are found in Pennsylvania: the Jefferson salamander Jefferson Salamander (Ambystoma jeffersonianum), the Marbled Salamander (Ambystoma opacum), and the Spotted Salamander (Ambystoma maculatum).  Mole salamanders breed almost exclusively in seasonal wetlands that do not support fish and therefore are considered seasonal pool indicator species.

The mole salamanders spend the majority of the year feeding in subterranean tunnels in the woodlands that surround seasonal pools.  Their diet consists of snails, worms, insect larvae, spiders, isopods, crickets, and other small animals they encounter.  This underground lifestyle makes them difficult to find during most of the year.  But once a year, they emerge to the surface and migrate to seasonal pools where males and females find each other, court, breed, and lay eggs.  The time for egg and larval development varies by species and by local environmental conditions.  As young salamanders (larvae), mole salamanders are aquatic and breathe through gills.  As adults, they become terrestrial and breathe with lungs. 

Jefferson Salamander Ambystoma jeffersonianum

Adult Jefferson salamanders are slate gray or brownish with pale blue flecking that is heaviest on their sides.  They average 41/4 to 7 inches in length; males are smaller than females (Conant and Collins, 1998).  Jefferson salamanders move to seasonal pools to breed very early in the spring; movements even occur when snow and ice cover the ground. 

Jefferson salamanders usually lay their eggs between March and early April.  The female lays a series of small egg masses each attached to vegetation or branches in the pool.  These egg masses tend to be smaller and less firm than those of the spotted salamander.  They are also more slender and cylindrical than the rotund spotted salamander egg masses.  Jefferson egg masses are clear and hard to see in the water although they often will turn a greenish color from algae.  The eggs develop for a period of thirty to forty-five days and hatch in April and May.  The larvae grow for three to four months and transform into immature terrestrial adults from July through August (Hulse, 2001). 

  Spotted Salamander Ambystoma maculatum

Adult spotted salamanders have bright yellow spots on a dark black to bluish -black background.  They average seven inches in length with no difference in body length between males and females (Hulse, 2001).  Spotted salamanders move to seasonal pools to breed early in the spring, though they usually move later than the Jefferson salamanders. 

Spotted salamandersgenerally lay their eggs between mid-March and mid-April.  The small, firm egg masses often contain 100 or more eggs in a cluster (Shaffer, 1991).  The eggs are attached to vegetation in the pool or reston thebottom. Egg masses may be clear or milky-white, and over time often develop a greenish color from algae. Spotted salamander egg masses tend to be more rotund in shape than Jefferson egg masses, which are more slender and cylindrical.  The eggs develop for a period of thirty to fifty days and hatch out from mid-May to June.  The larvae transform into immature terrestrial adults from August through September (Hulse, 2001). 

Spotted salamanders are found in upland or lowland deciduousforests or mixed hardwood-coniferous forests that support seasonal pools.  They prefer shallow pools with emergent vegetation where they can attach their egg masses, and pools with thick leaf litter on the bottom where the larvae can hide (Hulse, 2001). 

Marbled Salamander Ambystoma opacum

Adult marbled salamanders are black with silver or white bands across the body.  There is much variety in the appearance of the bands, but they are often expanded at the ends.  Marbled salamanders are stocky and shorter on average than the other mole salamanders. The average length for males and females is around four inches; females are slightly larger than males (Hulse, 2001).

The marbled salamander differs from the Jefferson and spotted salamanders in its reproductive cycle.  Adult marbled salamanders migrate to seasonal pools to court and mate in early fall rather than in the spring.  The female lays eggs sometime between September and November, depending mostly on local temperatures.  She constructs a nest for her clutch of 48-200 eggs in the autumnal pool basin under leaves, logs, or rocks (Hulse, 2001).  She usually stays at the nest protecting the eggs, until the pool begins to fill with water from rainfall or snowmelt.

The embryos hatch soon after the nest is inundated with the rising waters of the seasonal pool. The marbled salamander larvae gain a size advantage by feeding and growing for several months before the Jefferson and spotted salamanders hatch later in the spring. Marbled salamander larvae are also the first of the mole salamanders to complete their larval development, a process that takes about four and a half months from hatching to transformation into immature terrestrial adults that leave the pool (Hulse, 2001).  More information is needed on the distribution and habitat needs of this species.  In general, marbled salamanders utilize seasonal pools in upland forests that flood during the winter and spring.

NOTE: Another species of mole salamander may occur in Pennsylvania.   The blue-spotted salamander (Ambystoma laterale) is very similar in appearance to the Jefferson salamander.  This species is known from New York, and there have been a few reports from northeastern Pennsylvania.  The status of this species is uncertain; it may be breeding with the Jefferson salamander, creating a hybrid between the two species (Hulse, 2001). 

Eastern Spadefoot Scaphiopus holbrookii holbrookii

The eastern spadefoot is often called a toad because it resembles one, but it is actually a primitive species of frog that spends most of its life underground, feeding on insect larvae and adults (Hulse, 2001).  They are small, measuring 1 3/4 to 2 1/4 inches in length (Conant and Collins, 1998).   They have strong legs and webbed hind feet, equipped with a hard, sharp projection used as a digging ‘spade’. 

Spadefoots emerge to breed after intense rainfall such as heavy thunderstorms in the spring or summer.  When conditions are right, all the spadefoots in a local area may emerge, move to seasonal pools, breed, lay eggs, and return underground within a few days. 

Because it is dependent on sudden bursts of heavy rainfall, development in the spadefoot is accelerated compared to other seasonal pool species.  Eggs can hatch in only 24 hours, and larvae metamorphose into adults in 28 to 63 days (in Hulse, 2001).

Wood Frog Rana sylvatica

The wood frog is brown, reddish brown or copper colored with a white belly.  A distinguishing feature is a dark brown mask that stretches across its eyes.  As an adult it reaches between 1 3/8 and 2 3/4 inches in length (Conant and Collins, 1998).  Wood frogs have a special adaptation for surviving the winter months.  They stay in burrows or under leaf litter beneath the snow.  When temperatures drop, they increase glucose production to high levels, which acts like an antifreeze that keeps them from freezing solid.  This glucose antifreeze works down to a temperature of 20 degrees Fahrenheit  (Hulse, 2001).   Since the temperature at ground level rarely drops below that, they are protected from winter’s cold.             

Wood frogs spend most of the year in wooded upland habitats.  They migrate to seasonal pools in the spring where they breed and lay their eggs.  Males travel to the pools during the first rains of spring and begin calling to females with a distinctive quacking call.  Their mating call has often been described as “ducks in the woods”.  Their egg masses contain hundreds of eggs.   Unlike the Jefferson and spotted salamander egg masses, wood frog egg masses are not enclosed in a firm matrix that helps the egg mass retain its shape.  Wood frog egg masses are large, soft, and shapeless.  Often wood frogs will deposit their eggs in communal nesting areas, creating large expansive egg masses.   Like the salamander egg masses, wood frog egg masses often turn green from algae.

The eggs develop for roughly 20 days, dependent upon temperature.  Tadpoles are in the water for 80 to 115 days, emerging from the water in July and August (Hulse, 2001).

Facultative Species

Seasonal pool facultative species are ones that use seasonal pools for some part of their life cycle.  Facultative species have physical or behavioral adaptations that allow them to successfully utilize seasonal pools but they can also survive in permanent wetland habitats.

Red-spotted newt, Notophthalmus viridescens

The red-spotted newt is found throughout the state in upland areas. They utilize both temporary and permanent bodies of water to complete their life cycle. Adult body lengths vary from 2 1/4  - 4 13/16 inches (Conant and Collins, 1998).  Newts have a more complex life cycle than other salamanders because there is a distinct sub-adult stage.  Eggs are deposited in still water. 

The larvae develop and approximately three months later leave the water as immature terrestrial adults (Hulse, 2001).  This “red eft” stage (shown in the picture to the left) lasts for several years.  Once they become sexually mature, they return to the water and live an aquatic life.  The photos show the dramatic difference in coloration between the red eft stage and the aquatic adult. The red eft has granular orange-red skin; adult newts have smooth olive green skin.  Both the eft and adult stages have red dots outlined in black on the back and tail.

Four-toed salamander, Hemidactylium scutatum

This small salamander measures only 2 3/8 to 2 7/8 inches in total length.Males have a shorter body than females (Hulse, 2001). They are named four-toed because both front and hind feet have four toes; other salamanders have five toes on the hind feet.  The four-toed salamander has a reddish-brown back with black mottling.  The ventral surface has irregular black blotches that stand out against a white underside.  They are strongly associated with sphagnum moss and are found in forested areas that have bogs, marshes or woodland pools. Females nest in moss that overhangs or is near the edge of standing water.    The eggs hatch and enter the water to go through an aquatic larval stage.

American toad, Bufo americanus

This is the common hop toad found in many backyards across the state. It averages 2 to 3½ inches in length (Conant and Collins, 1998).  American toads exhibit a sexual dimorphism; males are smaller than females. The paratoid glands found on the back of the head can secrete a toxin to discourage predators.
American toad eggs are easy to identify because they are laid in long spiral strings, not singly or in clumps.

Fowler's toad, Bufo woodhousii

This toad is similar in size to the American toad, and is 2 ½ to 4 inches in length (Conant and Collins, 1998). Fowler’s toad usually has three or more large warts on each large dark spot on its back while the American toad has only one or two large warts.  The American toad has spots on the chest and belly while Fowler’s toad has an unmarked ventral surface.

Gray treefrog, Hyla versicolor/ chrysocelis complex

The skin on this tree frog is rather rough and pebbly looking with a dark irregular blotch on the back. It is well camouflaged for a summer spent foraging in the trees. This photo shows how well they blend in with their surroundings. Average length is 1 ¾ to almost 2 inches  (Hulse, 2001).  Another identifying mark on this amphibian is the bright dandelion-colored yellow skin on the inside of its legs.  The gray treefrog has particularly large toepads, which allow it to move about in trees with ease.

There are two species of gray treefrogs in Pennsylvania: Hyla versicolor and H. chrysocelis.  The two species are difficult to separate based on visual appearances.  Their calls can be used to identify them.  H. versicolor is a common species found statewide.  H. chrysocelis may be a rare find in PA, Hulse (2001) reports the potential for H. chrysocelis in southwestern Pennsylvania.

Spring peeper, Pseudacris crucifer

The key identifying feature of this small tree frog is the “X” on its back. Adults are approximately 1 to 1 ¼  inches in length (Hulse, 2001).  Like all the tree frogs, they have toe discs that allow them to live in the trees after the breeding season is over.

Calling spring peepers are often heard but seldom seen. Males call to establish a territory and to attract a mate. The inflated vocal sac is filled with air and acts as a resonating chamber to amplify the sound they make.

The eggs of Pennsylvania's frogs and toads are fertilized externally. The male grasps the female from behind (amplexus) and as she drops her eggs into the water, he fertilizes them.

Striped Chorus frog, Pseudacris triseriata

The striped chorus frog is a small tree frog species measuring slightly more than an inch in length (Hulse, 2001).  As the name implies, this frog is identified by the presence of three dorsal longitudinal stripes.

Three subspecies of the striped chorus frog are found in Pennsylvania:  Pseudacris triseriata triseriata, the western chorus frog; P.t. feriarum, the upland chorus frog; and P.t. kalmi, the New Jersey or coastal plain chorus frog.  They are probably easiest to separate based on geographical range.  The western chorus frog, not pictured, is found in the westernmost tier of counties and has three broad longitudinal stripes. 

The upland chorus frog (P.t. feriarum) occurs primarily in the mid and southcentral counties of the state; it has three thin stripes that are often broken. 

The New Jersey chorus frog ( P.t. kalmi) is found only on the coastal plain in the southeastern part of the state. It typically shows three broad stripes, and has a more robust build than the other two subspecies (Hulse, 2001).

Bullfrog, Rana catesbeiana

This is our largest frog.  Both males and females average 4 ¾ inches in length (Hulse, 2001).  They will consume whatever fits into their mouth, which has a considerable gape. They are easily identified by their deep bass call. While somewhat similar in appearance to the green frog, they are distinguishable by the complete lack of dorsolateral folds on the back. Male and female bullfrogs can be identified by the size of the tympanum in relation to the eye. If the tympanum is similar in size or larger than the eye, the frog is a male. If the tympanum is smaller than the eye, it is a female. This sexing method also holds true for the green frogs.

Green frog, Rana clamitans

The true frogs, which include the green frog, bullfrog, leopard and pickerel frogs, have smooth skin with dorsolateral folds on their backs and long legs with webbed toes. The green frog adult measures 2¼ to 3½ inches in length.  It is bright to dark green or brown on the dorsal surface, but is most easily distinguished from similar species by the dorsolateral folds, or raised skin extending in a line from the eye to the middle of the abdomen.

Pickerel frog, Rana palustris

The average adult length of the pickerel frog is 21/8 to 2½ inches; females are slightly larger than males (Hulse, 2001). This frog has two rows of rectangular spots between the dorsolateral folds on the back and the yellow inner thighs.  Both the pickerel and leopard frogs have paired vocal sacs. All other Pennsylvania frogs and toads have but a single sac under the chin. These sacs are only visible when the frog is calling.

Northern leopard frog, Rana pipiens

Adults average 2 to 3½ inches in length (Conant and Collins). Dorsolateral folds run down the back all the way to the groin. Unlike the similar looking pickerel frog, the dorsal spots are rounded and are not in neat rows on the back. The inner thighs lack the yellow coloration found on the pickerel frog.

The northern leopard frog is similar in appearance to the southern leopard frog.  The range where the frogs are found can also be used to separate the two species.  The northern leopard frog occurs most frequently in the western third of the state and in portions of the Valley and Ridge Province.  The southern leopard frog is found only in the extreme southeastern corner of the state (Hulse, 2001). 

Southern leopard frog,  Rana sphenocephala

This frog is known only from the southeastern part of the state.  It is very similar in size and appearance to the northern leopard frog but can be distinguished by the presence of a light spot on the center of the tympanum.  

Photo Credits

Wood frog:  Ben Jellen
Jefferson salamander, wood frog eggs, spring peeper amplexus : Sally Ray
Four-toed salamander, adult red-spotted newt : Charlie Eichelberger
E. spadefoot, S. leopard frog, NJ chorus frog: Tom Diez
All others: Jack Ray