Illinois Chorus Frog

Image of an illinois chorus frog
Species of Conservation Concern
Scientific Name
Pseudacris illinoensis
Hylidae (treefrogs and allies) in the order Anura (frogs)

The Illinois chorus frog is Missouri's largest chorus frog. It is chubby, with large, muscular, almost toadlike forelegs. The general color is light tan to tannish gray. There is a distinct V-shaped mark between the eyes, a dark stripe from the snout to the shoulder, and usually a dark spot below the eye. A pair of large, dark, irregular V-shaped markings are present on the back behind the head. These markings are dark gray to brownish gray. The skin is rough or granular. The belly is white. The toe pads are small and round, and the webbing of the hind feet is poorly developed.

The breeding call of males is a clear, quick series of high-pitched, birdlike whistles.

Similar species: In the hylid family, nine species, in three genera, are native to Missouri:

  • Acris, the cricket frogs, one species: Blanchard’s cricket frog;
  • Hyla, the treefrogs, three species: gray treefrog, Cope’s gray treefrog, and green treefrog; and
  • Pseudacris, the chorus frogs, five species: spring peeper, upland chorus frog, Cajun chorus frog, Illinois chorus frog, and boreal chorus frog.

Adult length (snout to vent): 1 to 1½ inches; occasionally to nearly 2 inches.

Where To Find
Illinois Chorus Frog Distribution Map

In Missouri, restricted to the southeastern corner. This species has a very limited range in North America, including only west-central and southwestern Illinois, southeastern Missouri, and one county in extreme northeastern Arkansas.

In Missouri, the Illinois chorus frog prefers flat, sandy areas. Originally, these frogs lived in the natural sand prairies and sand savannas of southeastern Missouri, but this habitat has been nearly eliminated. However, Illinois chorus frogs continue to survive in soybean and cotton fields in the former sand prairie area.

Unlike other fossorial (burrowing) species, such as true toads and spadefoots, the Illinois chorus frogs enter the soil headfirst using their strong forelegs and forefeet for digging. They are excellent burrowers in sandy habitat and are known to remain 6–8 inches below the surface for most of the year. During winter, they must burrow down more than 10 inches to survive cold temperatures. They tend to burrow in open areas away from any vegetation.

Breeding sites are flooded depressions in crop fields, roadside ditches, and other fishless, temporary pools.

Habitat changes and loss have led to diminished populations of this unique burrowing frog. See the Status section for more information about conservation.

The tadpoles eat suspended matter, organic debris, algae, and plant tissue.

The feeding behavior of adult Illinois chorus frogs is difficult to study because apart from breeding time, when they are aboveground, they usually eat while burrowing headfirst underground. Their hunting is aided by their grasping forefeet, which can catch and hold prey. Apparently, during the months they spend living in the sandy soil, they swallow a lot of sand while they burrow and hunt. A 1997 study showed the frogs primarily eating dingy cutworms (the caterpillar of a noctuid moth, Feltia jaculifera), which were notably abundant during the week of that study. However, these frogs also eat other species of moth caterpillars, plus beetles, spiders, true bugs, flies, and ants. Beetle larvae (grubs), in particular, frequently live in the soil and no doubt are an important food. Apparently, Illinois chorus frogs feed opportunistically on whatever insects they can capture — and most of their season is spent underground.

A Missouri species of conservation concern, listed as imperiled by the Missouri Department of Conservation. Currently a candidate for federal listing by the U.S. Fish and Wildlife Service. It occurs only in parts of Illinois, the Missouri Bootheel, and in extreme northeastern Arkansas.

Extensive agricultural practices in the sand prairie regions of the Missouri Bootheel have destroyed or modified nearly all the natural ephemeral pools where this species formerly bred. In addition, housing developments and other land uses have reduced or eliminated the sand prairie sites. Although this frog is still present in the highly cultivated areas of southeastern Missouri, there is concern whether these amphibians can withstand the continued destruction of their remaining habitat, especially wetland loss. Surveys over the years for this species have failed to locate breeding colonies in Pemiscot and the southern half of Dunklin counties, and it is likely the historic populations in these counties are extirpated. However, large numbers of frogs are still present in the core sand prairie regions of Scott, Mississippi, New Madrid, and the northern half of Dunklin counties. Long-term persistence of this unique, burrowing frog in southeastern Missouri is dependent on maintaining wetlands for them to reproduce.

This frog was formerly considered a subspecies of the Strecker’s chorus frog (Pseudacris streckeri illinoensis); in 2004 the Illinois chorus frog was given full species status.

Life Cycle

The Illinois chorus frog breeds in late winter and early spring — usually late February to early April — depending on local weather conditions. Breeding sites are flooded depressions in crop fields, roadside ditches, and other fishless, temporary pools. The males call while floating in the water or hanging onto grassy vegetation. Females lay about 150–1,000 or more eggs, with an average of about 460. The eggs are laid in masses of about 8–100 eggs. The eggs hatch in about a week. The tadpoles, which are large compared to those of other chorus frogs, may take up to 60 days to transform into froglets. Juveniles become sexually mature about a year later. Lifespan is about 2–5 years, but because these frogs spend most of their time underground, the lifespan may actually be longer.

Agricultural development in the Bootheel has destroyed nearly all the natural ephemeral pools where this species formerly bred, and housing development has nearly eliminated the sand prairie. This frog still lives in some highly cultivated areas but may not survive continued habitat destruction. The survival of this unique, burrowing frog in southeastern Missouri is dependent on maintaining wetlands for them to reproduce.

Ecosystems have been likened to jets, and species of plants and animals as the plane’s components. If a species of gnat, grass, violet, or frog disappears, it might be like losing a rivet from a wing. A few missing rivets may not affect the jet’s safety — but at some point, if enough components disappear, it will crash.

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About Reptiles and Amphibians in Missouri
Missouri’s herptiles comprise 43 amphibians and 75 reptiles. Amphibians, including salamanders, toads, and frogs, are vertebrate animals that spend at least part of their life cycle in water. They usually have moist skin, lack scales or claws, and are ectothermal (cold-blooded), so they do not produce their own body heat the way birds and mammals do. Reptiles, including turtles, lizards, and snakes, are also vertebrates, and most are ectothermal, but unlike amphibians, reptiles have dry skin with scales, the ones with legs have claws, and they do not have to live part of their lives in water.