outside the Chicago area has been reported froin 

 March to May. Males have double vocal sacs that pro- 

 duce a low-pitched, musical snore lasting one or two 

 seconds, and males may call while they are submerged. 

 A globular clutch of 2,000-3,000 eggs is usually laid in 

 clear, shallow water with a temperature between 50° 

 and 65°F. These hatch in 10 to 14 days. 



Northern leopard frogs, Ranapipiens, are common 

 and frequently encountered around streams and ponds. 

 They may be brown or green, with two or three rows of 



Pickerel frog. Rana palustris 



round spots on the back; the spots may be scattered, 

 run together, or missing entirely. These frogs average 2 

 to 3.5 inches long, but sometimes exceed 4 inches. 

 Males call with paired vocal sacs from shallow, stag- 

 nant water with vegetation, and may call while sub- 

 merged. This habit makes them difficult to be heard 

 and more difficult to locate. The sound has been 

 likened to that made by rubbing a finger over an in- 



Northern leopard frog, Rana pipiens 



flated balloon, but it often consists of a one deep snore 

 that is interrupted with a clucking grunt that lasts 

 about a second. Three to five thousand eggs are laid 

 between March and May in spherical masses and the 

 eggs hatch in about seven days. The tadpoles transform 

 from June to August. Adults spend the summer months 

 replenishing their energy supply by capturing insects 

 and spiders in grassy habitats near their egg-laying sites. 

 Leopard frogs have long been used as laboratory ani- 

 mals and, as such, one would think that everything 

 would be known about these frogs; that is not so. 



The plains leopard frog, Rana blairi, was described 

 in 1973. Until then it had masqueraded as the north- 

 ern leopard frog. It is widely distributed in the central 

 plains, but its separate identity was not noted because 

 of the similarity in appearance to its sister species. Ex- 

 ternally, the plains leopard can be distinguished from 

 the northern leopard by a broken fold of skin on each 

 side of the back, and occasionally by yellow coloration 

 on the abdomen and thighs. Another major difference 

 is in the pulse rate of the mating calls; the plains 

 leopard frog calls at about five or six pulses per second, 

 while the northern leopard frog calls at a pulse rate of 

 about twenty per second at temperatures below 75°F. 

 Further complicating the leopard frog situation is a 

 third species found in the southern part of the state — 

 the southern leopard frog, Rana sphenocephala. 



Three other frogs that inhabit Illinois are found at 

 the southern end of the state and tend to be restricted 

 in distribution or very secretive. The northern crayfish 

 frog, Rana areolata circulosa, gets its name from spend- 

 ing much of its time in crayfish burrows, as well as from 

 eating small crayfish. The great plains narrowmouth 

 toad, Gastrophryne carolinensis, is small and squat, has a 

 collar-like fold of skin behind its head, runs on all four 

 feet in a very unfrog-like way, and spends much of its 

 time eating ants. The eastern spadefoot toad, Scaphious 

 holbrookii, is subterranean, coming to the surface to re- 

 produce after heavy rains. Fll 



Suggested Readings 



R. Conant: A Field Guide lo Reptiles and Amphibians of Eastevi and 

 Central North America, 429 pp., 1975, Houghton Mifflin. 



C. Pope: Amphibians ami Reptiles of the Chicago Area, 275 pp. , 

 1944, Chicago Museum of Natural History (Field Museum). 



P. Smith: The Amphibians and Reptiles of Illinois. 298 pp., 1961, 

 State of Illinois, Dept. of Registration and Education, Natural 

 History Survey Division. 27 



