Herpetology of Illinois

By Stephen L. Barten, DVM, and Michael Dloogatch

Illinois is a large state, measuring 385 miles from north to south and 215 miles from east to west. Because of its size and location in the central part of the United States, Illinois is populated by a rich variety of reptiles and amphibians, numbering 103 species. This includes 20 species of salamander, 21 frogs and toads, 17 turtles, 7 lizards (one species of which was introduced) and 38 snakes. Part of the reason a relatively northern state can host such a variety of reptiles and amphibians is that a number of species found in neighboring states have ranges which barely overlap into Illinois. Within its borders lie the westernmost ranges of several eastern species, the southernmost ranges of some northern species, the easternmost ranges of some western species, and the northernmost ranges of quite a few southern species. Thus a number of reptiles and amphibians more common in the Ohio River valley, Wisconsin and Canada, the great western plains, and the Gulf Coast can all be found in Illinois.

Most of the original habitat within the state has been destroyed by man. During the last century, almost all of the original prairie was converted to agricultural fields. In fact, Illinois has been described as a great corn desert. More recently, urban sprawl is eradicating what little habitat had been spared by agricultural use. Natural prairies, forests, river bottoms and the like have been reduced to focal, isolated habitats with few corridors for animals to use for safe passage between them. Nevertheless, reptile and amphibian distribution is determined by the location of current or former biotic provinces or ecosystems

Smith (1961) divided the state into herpetological divisions coinciding with the two main ecosystems: prairie and forest. These areas were further subdivided into smaller, more defined areas, each containing certain representative species as well as a number of species distinctive to each given area. The prairie can be divided into grand prairie, outlier prairies and sand prairies, while the forest is divided into northeastern mesic forest, western division, southern division and river borders.

The Grand Prairie is that area of original prairie in the northern half of the state, excluding sand prairies, that was once covered by glaciers. Common species here include the American toad, plains garter snake, fox snake and bull snake. Kirtland’s snake and Blanding’s turtle, now rare, must have been more common before widespread cultivation changed local habitat. Kirtland’s snake, the lined snake and the smooth green snake are peculiar to this habitat.

The Outlier Prairies are interspersed with forest in the southern half of the state. Abundant species here include the smallmouth salamander, Fowler’s toad, racer, prairie kingsnake and eastern hognose snake. Distinctive species are the crawfish frog and ornate box turtle.

The Sand Prairies consist of small, well-defined areas with limited distribution along the eastern borders of the Mississippi and Illinois Rivers, portions of northwestern Illinois and sections of both Kankakee and Iroquois Counties. Species more commonly found west of the Mississippi River are abundant here, including six-lined racerunners, ornate box turtles, bull snakes and western hognose snakes. Racers and eastern hognose snakes are also common here. The Illinois chorus frog and Illinois mud turtle are endemic subspecies peculiar to these habitats. Salamanders are rare in sand prairies, and Fowler’s toad outnumbers the American toad here, the reverse being true throughout the rest of the state.

The Northeastern Mesic Forest, in the northeastern corner of the state along Lake Michigan, contains a rich variety of northern and eastern species. Spotted salamanders, wood frogs, eastern milksnakes, redbelly snakes and queen snakes are typical of this habitat. The blue-spotted salamander, four-toed salamander, spotted turtle and Chicago garter snake, a disputed subspecies of the eastern garter snake, are unique to this area within the state.

The Western Division consists of patches of forest interspersed with prairie in the western part of the state. It contains relatively fewer herps, and those species found here are common elsewhere in the state as well. Representative species include northern cricket frogs, striped chorus frogs, northern leopard frogs, green frogs, eastern garter snakes and eastern milksnakes.

Smith (1961) subdivides the southern part of the state into the Southern Division, Shawnee Hills, Wabash Border and Austroriparian Divisions. For our purposes, these may be lumped together. Southern Illinois contains rocky bluffs and outcrops, forest, thicket and river bottoms. Many southern species of herpetofauna extend into the southern third of the state. Common species found here include the marbled, northern slimy, longtail and smallmouth salamanders; spring peeper, gray treefrog and Fowler’s toad; fence lizard and both five-lined and broad-headed skinks; eastern box turtle; and the copperhead, black rat snake, smooth earth snake, rough green snake, midland water snake, plainbelly water snake and red milksnake. Species common to the Gulf Coast of the United States whose ranges extend into southernmost Illinois include the mole salamander, green treefrog, bird-voiced treefrog, eastern spadefoot, cooter, alligator snapping turtle, mud snake, Mississippi green water snake, scarlet snake and cottonmouth.

The Upper Mississippi Border is characterized by the presence of the green frog, northern water snake, ringneck snake, black rat snake and eastern garter snake. Distinctive species include the longtail salamander, worm snake and pickerel frog. The Lower Mississippi Border, south of Saint Louis, contains many of the same species found in both the Upper Mississippi Border and Shawnee Hills. In addition, several species enter the state here from the west and are found nowhere else. These include the eastern narrowmouth toad, coachwhip snake, Great Plains rat (corn) snake, and flathead snake.

Several species of reptiles, although they may be common elsewhere, are protected in the state of Illinois because their range barely enters the state, and thus the local populations are vulnerable. These include the spotted turtle, alligator snapping turtle, Great Plains rat (corn) snake, coachwhip, and western hognose snake.

There are only four species of venomous snake within the state. The cottonmouth is found only in the southernmost tip of the state. The copperhead inhabits the southern third of the state. The timber rattlesnake also inhabits the southern third of the state, as well as areas along the Illinois and Mississippi Rivers. The eastern massasauga is a small species of rattlesnake found in isolated populations throughout much of the state. The cottonmouth and copperhead are relatively common where they are found, but the two species of rattlesnake have been reduced to small, disjunct, relictual populations spotted here and there within their historical range. The timber rattlesnake is listed as a threatened species in Illinois. The massasauga population is so reduced that the species is now listed as endangered in Illinois.

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