Wood frog, Rana sylvatica 



Bullfrog, Rana catesbiana 



and green treefrog are gulf plain species, extending 

 their range into extreme southern Illinois. 



The true frogs, family Ranidae, is a collection of 

 about 650 species that is almost worldwide in distribu- 

 tion. It contains many species that are less than one 

 inch long, but it also contains the world's largest frog, 

 the African goliath frog, Conraua goliath, that has a 

 body length of 12 inches. The habits of ranid frogs are 

 as variable as their body sizes, but all of the Illinois 

 species have webbed feet, free fingers (fingers that lack 

 webbing), smooth skin, long legs, and narrow waists. 

 Males may have single or paired vocal sacs, one on each 

 side of the throat. 



The wood frog, Rana sylvatica, is the only frog in 

 the Chicago area that has a dark brown mask through 

 each eye. Adults are 1.5 to 3 inches long, males being 

 smaller than females. Wood frogs are active in late Feb- 

 ruary or early March, appearing in woodland ponds and 

 breeding as soon as the air temperature reaches 50°F. 

 During the breeding season males are darker than 

 females and have swollen thumbs. Males also have 

 paired vocal sacs and a duck-like hoarse cackling voice 

 which says "waaaduck," lasting about one second. 



