Frogs and toads live in a variety of habitats but are seldom found far from water. They also live in dark, moist places such as under rocks, boards, logs and leaves. Some spend much of their life underground or in the branches of trees and shrubs. Frogs and toads are generally active at night when the air contains more water than during the day, and it is easier for them to keep their skin moist.
Adult frogs and toads are carnivores that feed on worms, insects, spiders and other small invertebrates. Large frogs, such as the green frog and bullfrog, will eat any prey that they can catch and swallow including fishes, crayfish, snakes and other frogs.
Frogs and toads gather near water in the spring or summer to breed. Males generally appear first and begin calling to attract females. Calls are made by passing air back and forth across vocal cords. A vocal sac or pair of sacs functions to intensify and prolong the call. The calls are species-specific. Soon after calling begins, the females appear and seek out the males of their species.
The male and female come together and release eggs and sperm into the water. The eggs may be in strings or masses below the water’s surface or as a film on the water’s surface. Often the eggs are attached to plants or other objects in the water. The number of eggs laid by a female varies from about 100 for the western chorus frog (Pseudacris triseriata) to as many as 40,000 for the bullfrog (Lithobates catesbeianus). For some species, hatching can occur one or two days after the eggs are fertilized. It may take 14 days for the eggs of other species to hatch. The tadpoles eat plankton, algae and plants. The transformation from tadpole to froglet takes 12 days for the eastern spadefoot (Scaphiopus holbrookii) but may take up to two years for the bullfrog.
Frogs and toads are prey for fishes, reptiles, birds and mammals. Most of these amphibians do not live as long as one year. Some bullfrogs have been known to live more than 10 years, but it is doubtful that many frogs in the wild live so long.
Because frogs and toads lack feathers and hair, because their body temperature is mainly determined by that of their surroundings and because most of their prey species would not be available, they cannot remain active and survive Illinois’ winters. They seek refuge in places where the humidity is high and the temperature remains above freezing. They enter a state of dormancy called brumation. Frogs and toads brumate under debris, in the soil or in water. During this period, all breathing occurs through their skin.
The eastern spadefoot (Scaphiopus holbrookii), (2.25 inches) can be identified by the pair of light lines on its back and by the vertical pupil in the eyes. This animal is found in extreme southern Illinois often in sandy or other loose soils. It lives mostly underground and breeds from March to September after heavy rains. Its call can attract other spadefoots from at least one-half mile away and sounds something like an explosive nasal grunt.
The American toad (Anaxyrus americanus), (2.0-3.5 inches) has enlarged bumps or “warts” on its hind legs and one or two large “warts” in each spot on its back. This species is the common toad of northern Illinois, and it is often encountered in lawns, orchards and gardens. It breeds in shallow pools from March to July with most activity occurring about mid-April. Its call is a sustained, high, musical trill.
Fowler’s toad (Anaxyrus fowleri), resembles the American toad, but the large spots on its back contain three or more “warts.” The “warts” on its legs are not enlarged. This toad is common in the southern one-half of Illinois. Although it is abundant in almost all suitable habitats, it has a tendency to occupy sandy areas and stream margins. Its eggs are laid in long strings. Its call sounds like a prolonged nasal scream or bleat.
The cricket frog (Acris crepitans), (1.5 inches) has variable coloration but almost always has a dark triangle between its eyes. It is found statewide in almost any wet place, especially the sunny banks of lakes and streams. The cricket frog begins breeding in late April and continues throughout the summer. The call is a series of rapid metallic clicks, much like that produced when striking two pebbles or marbles together.
The western chorus frog (Pseudacris triseriata), (1.5 inches) has three dark lines on its tan, gray or green-gray back. Sometimes the lines are broken into a series of spots. This frog is found throughout Illinois and is one of the first frogs to appear in spring. It begins breeding after warm rains in early March and continues into May. After the breeding season, these secretive creatures are seldom seen. The call is heard day and night and can be imitated by passing a fingernail over the teeth of a plastic comb.
Strecker’s chorus frog (Pseudacris streckeri), (1.75 inches) is light gray or brown with a few dark bars on its back. A dark V- or Y-shaped marking is located between the eyes. This chubby frog is toad-like in its habits. Unlike toads, however, it digs head first into loose soil. True toads dig backwards into the ground. This species is Illinois’ rarest frog and is classified as a threatened species. It is found in shady woods, streams or sand prairies in only a few counties in western, southwestern and southern Illinois. Strecker’s chorus frog lays its eggs in shallow water during March. Its call is a series of clear, bell-like notes.
The upland chorus frog (Pseudacris feriarum), (1.5 inches) has a dark line on each side of the body that starts on the snout, passes through the eye and continues along the side. The three, thin lines on the back may be broken into spots. It is found in the southern tip of the state in forests, forest edges and marshy fields. Its call is similar to that of the western chorus frog.
The boreal chorus frog (Pseudacris maculata), (0.75-1.25 inches) is brown to gray with three dark lines down the back and another through the eye. There is a white line along the upper lip. It is very similar in appearance to the western chorus frog. Although usually found in shallow ponds, wetlands and other water bodies without a current, individuals of this species may live in grasslands, meadows, urban areas and forests in summer. The boreal chorus frog can be found in all of Illinois except the southeastern one-fourth of the state. The male’s call is a trill that can be imitated by running a fingernail along the teeth of a comb.
The bird-voiced treefrog (Hyla avivoca), (1.5-2.0 inches) is a threatened species in Illinois. It is identified as a treefrog by its enlarged, sticky toe pads. Its gray, brown or green back often has an irregular, star-shaped blotch. A wash of green or yellow can be seen on the inner thighs. They live in extreme southern Illinois where they breed from mid-May to August in the wooded swamps of cypress and buttonbush. Their call resembles a ringing, bird-like whistle.
The green treefrog (Hyla cinerea), (1.25-2.25 inches) lives in the swamps, lakes and streams of southern Illinois. It breeds from mid-May to August. A chorus of calling males sounds like the clink of cowbells, while an individual green treefrog sounds like a nasal “quonk-quonk-quonk.”
The tiny spring peeper (Pseudacris crucifer), (1.0 inch) is found statewide and can be recognized by the dark “X” mark on its back and the dark line between its eyes. The skin is usually tan or brown with a pink cast. It is rarely seen except when breeding from early March to early June. It lives in moist, often brushy woodlands and lays its eggs in woodland ponds. During the day it calls from tree branches or from under leaves on the forest floor. At night, its piping, clear whistle can be heard from the water’s edge or from plants over water.
The gray treefrog (Hyla versicolor), and Cope’s gray treefrog (Hyla chrysoscelis), are so similar that they were once considered a single species. Both of these warty-skinned treefrogs average less than two inches in length. A light spot under the eye is characteristic, and the concealed surfaces of the hind legs are washed with orange. Both of these treefrogs live in moist woodlands, thickets and swamps where they breed from late April to August. Much of their time is spent hunting insects in small trees or shrubs over water. They seem to prefer living in hollow, dead trees or under moist, rotten bark, and they are rarely found on the ground except when migrating to breeding ponds. The only reliable way to separate these two species in the field is by their calls. The call of the gray treefrog is a slow trill lasting more than one second. It resembles the call of a red-bellied woodpecker, Melanerpes carolinus. The call of Cope’s gray treefrog is a higher and faster trill lasting less than one second.
The crawfish frog (Lithobates areolatus), grows to a length of nearly four inches. The skin has dark, round spots surrounded by light borders, and the back is noticeably “humped.” It lives in clay soils in the southern one-half of Illinois. A nocturnal frog, it spends the daylight hours hiding in crayfish or other animal burrows or under boards and logs in wet prairies, pastures and golf courses. It lays its eggs from early March to mid-April in flooded fields, farm ponds and small lakes. The call resembles a deep, roaring snore.
The bullfrog (Lithobates catesbeianus), is olive or brown above with some green on the head or upper jaw. It is the largest frog species in North America, reaching a length of eight inches. It is common throughout our state. This frog spends most of its time near permanent water. It is classified as a game animal and is hunted for its legs. From late April to August the eggs are laid in large surface masses, sometimes up to five feet across. The call has been described as a deep, bass “br-wum” or “jug-o-rum.”
The green frog (Lithobates clamitans), resembles the bullfrog in coloration. It differs from the bullfrog in having a pair of distinct ridges extending from the head for two-thirds of the body length. It rarely is larger than four inches in length. The green frog occurs in northern, western and southern Illinois. In northern Illinois, it is found in a variety of aquatic habitats, but in the central and southern portions of the state, it is restricted to clear, cool streams near rock outcrops. It breeds from May to September and, like the bullfrog, the tadpoles do not transform until their second summer. The call of the green frog sounds like the plucking of a loose banjo string.
The pickerel frog (Lithobates palustris), (1.75-3.00 inches) can be identified by the two rows of irregular square or rectangular spots on the back. It is usually gray or tan with bright yellow on the rear of the thighs and belly. This frog is found only in the extreme northern, western and southwestern portions of Illinois. In southern Illinois it can be found in floodplain swamps. Elsewhere, it lives in cool, clear streams and caves. The eggs are laid from April to mid-June. The call is a short, gruff snore.
The northern leopard frog (Lithobates pipiens), usually has two or three rows of irregular dark spots on the back. Each spot has a light margin. A dark spot on the snout is also common. This three and one-half-inch frog is found in northern Illinois. During the summer months, it wanders far away from the streams, ponds and sloughs where it normally lives to feed on insects in grassy or weedy fields. It breeds from mid-March to May. Its call can be imitated by rubbing a thumb over an inflated balloon.
The southern leopard frog (Lithobates sphenocephalus), is similar to its northern cousin. However, the spots rarely have a light border, and the snout rarely has a dark spot. A light marking often occurs on the eardrum. This frog lives in southern Illinois. It breeds slightly earlier than the northern leopard frog but lives in similar habitats. The mating call consists of a rapid series of short chuckles.
The plains leopard frog (Lithobates blairi), feeds in grassy areas away from water during the summer. It closely resembles the northern leopard frog except that the ridges on the back have a space in them near the hind legs. The inner thigh is washed with yellow. It occurs in central and southern Illinois in prairie remnants. Its call consists of two or three clucks per second.
The wood frog (Lithobates sylvaticus), has a black mark on the face, like a mask. Although usually pink or tan, it is sometimes darker in coloration. There is a dark mark on the shoulder. This uncommon one and one-half- to two and three-fourths-inch frog occurs in the forested areas of our state. The breeding season is very short, lasting only one or two weeks in March. The wood frog lays its eggs in woodland pools. This species often appears before the ice on ponds has melted. It is very tolerant of cold and ranges farther north than any other North American amphibian. The breeding call resembles the feeding chuckle of a duck.
The eastern narrowmouth toad (Gastrophryne carolinensis), (1.25 inches) has a fold of skin across the back of its pointed head that can be moved forward to protect its eyes. This small, plump toad is found only along the Mississippi and Ohio rivers in southern Illinois. It is a threatened species in our state. The narrowmouth toad hides by day under rocks, bark, rotten stumps or other objects on the ground. It comes out at night to feed on small insects. This unusual species breeds throughout the summer after heavy rains, and its call resembles the bleat of a lamb.