Wood Frog
Rana sylvatica

by Jeff LeClere

Status

Wood frogs have no status in Minnesota.

Description

This medium sized frog (2 1/2 inches, body length) presents a bewildering array of variation. There is always a black "mask" over the eyes. The ground color is gray, brown, reddish brown or rust. The back may be plain or mottled with black or brown. A white or light colored middorsal stripe may or may not be present. The belly is light, very rarely with a suffusion of dark mottling. There is a white line along the upper lip. The hind legs may have black bars. These bars may be dark, faint, or absent. There are distinct dorsolateral folds down the back. These may be light or dark, have black dots and dashes or may be clear.

Subspecies

Only one subspecies, the wood frog, Rana sylvatica, is found in Minnesota. There were once considered two subspecies in Minnesota based on length of hind leg. There are studies that are now looking at the importance of the light middorsal stripe.

Range

Wood frogs are found throughout Minnesota except in the southwestern and south central part. Populations are scattered and seemingly wide-spaced in southeastern Minnesota. They are common in northern and central Minnesota.

Habitat

Wood frogs, as their name implies, are a woodland species. They frequent the heavily timbered boggy forests of northern Minnesota. In central Minnesota they are also found in prairie and grasslands breeding in marshes surrounded by woodland. Interestingly, I have observed a very few wood frogs utilizing cold streams in the heavily forested blufflands of southeastern Minnesota. Apparently, they breed in woodland pools near these streams.

Habits

Wood frogs are one of Minnesota's earliest emerging herps. They emerge in late March or early April and begin breeding as soon as they reach the ponds. Often they are found calling in the open portions of ice covered marshes. The male's voice is a chuckling quack. A chorus sounds like a flock of ducks. Males vocalize while floating or resting on submerged vegetation. The vocal sacs are located on the sides of the body. The breeding season lasts two weeks at the longest. Males call night and day. Males attempt amplexus with anything they get a hold of. Amplexed males give a release call and struggle to let the aggressor know he has grabbed another male. Such struggling can cause quite a commotion and I see and hear several such encounters during a single breeding season.

Females lay a floating cluster of nearly 1,000 eggs. Often, most or all of the females will lay their eggs on one end of the pond creating a huge mat of eggs. Such clusters may increase the temperature of the masses at the center thus speeding the development of the eggs. These masses may also protect the inner clusters from predators such as leeches and aquatic insect larvae. The tadpoles morph in 1 1/2 to 2 months. The adults move away from the breeding ponds after the breeding season ends. Unlike many Minnesota frogs, wood frogs move considerable distances from permanent water. They search for food in moist heavy forests. They take shelter under leaf litter and rely upon camouflage for defense. They hibernate under rocks or logs and partially freeze like gray tree frogs.

Food

Wood frogs eat any small invertebrates they find in their woodland habitats.