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Wood Frog

Overview:

Scientific Name: Rana (Lithobates) sylvatica

Size: 1.4 – 3.3” (adult size)

Status: Can be abundant in suitable areas.

 

Habitat:

Inhabit moist wooded habitats including deciduous, coniferous, and mixed forests. Adults are mainly terrestrial except during the breeding season. Prefer closed canopy areas.  

Conservation:

Wherever woodlands enclosing or adjacent to suitable breeding ponds exist, Wood Frogs tend to be doing well. When forest cover is removed, or breeding sites are drained or filled they disappear. Migrating adults crossing roadways can be killed. Their eggs and larvae are sensitive to the runoff of road salt and acidic precipitation that can vary across populations.   

Best Management:

Pesticide application should occur in late summer and fall when larvae have metamorphosed, and hibernation begins. Consider the effects of altering or destroying vernal pools and other fish-free ponds. Do not impact the pool depression or core buffer area within 100 feet of the pools and aim to protect a wider buffer of 600 – 1000 feet around the pools. Try to maintain any habitat corridors to other vernal pools and upland habitats. Seasonally close roads or place structures over roads for crossing. Minimize the spread of salt on roadways near wetlands which can reduce the survival of pollution sensitive species. Avoid spring burns when individuals emerge from hibernation and avoid burning near wetlands where individuals will be taking cover.  

Adult Coloration:

Brown, greyish brown, bronze, reddish-brown or tan body color with a dark “mask” extending from the eye through the tympanum (circular “ear” structure on the side of the head) to the shoulder bordered by a white stripe on the upper lip. The mask extends to a narrow, dark stripe to the tip of the snout. Males may appear nearly black, and mask may be obscured during breeding, can have black spots along the dorsolateral folds (raised ridges running extending down each side of the back), sides, and dark bands on the hind legs. The belly is white with occasional grey mottling, sometimes they have a yellowish tint on the sides or groin. In the northern range they may have a light stripe down the back and on the hind legs. 

Adult Characteristics:

Dorsolateral folds extend from the eye down the back. In males the webbing between the hind toes is straight or has an outward curve. During the breeding season, males darken in color and their thumbs become thickened with an inner pad and the vocal sac become visible as the skin folds from the jaw to shoulder on each side. In females the edge of the webbing between the hind toes is curved inward and a larger and lighter in color. The call is a series of clucks, may sound like ducks from a distance. Can produce a chirp-like “release” call when clasped by another male during breeding.  

Larvae Characteristics:

Tadpoles can grow to be 1.8” in length with a plump body and a short, high tail fin. The body is brown or olive and speckled with black and gold. The tail is lighter with occasional black spots. The belly is iridescent white to pink or bronze and the intestines are visible through the skin.  

Species Confused With:

Chorus Frogs have a similar mask-like pigmentation and a light lip stripe but are substantially smaller, lack dorsolateral folds, and have expanded toe pads. 

References:

  • Amphibians and Reptiles of the Great Lakes Region by Jim Harding
  • Harding, J.H. and J.A. Holman. 1992. Michigan Frogs, Toads, and Salamanders. MSU Cooperative Extension Service and MSU Museum. Extension Bull. E-2350, 144 pp.
  • Ruthven, A. G., H. B. T. Gaige, et al. 1912. The herpetology of Michigan, by Alexander B. Ruthven. Crystal Thompson and Helen Thompson; Memoranda towards a bibliography of the archaeology of Michigan, by Harlan I. Smith; prepared under the direction of Alexander G. Ruthven. Lansing, Mich., Wynkoop Hallenbeck Crawford, State Printers.
  • Holman, J. A. 2012. The Amphibians and Reptiles of Michigan: A Quaternary and Recent Faunal Adventure. Detroit, Mich., Wayne State University Press.
  • Conant, R., and Collins, J. T. 1998. Reptiles and Amphibians: Eastern, Central North America. Houghton Mifflin Harcourt Press.