Northern Leopard Frog

IUCN Red List

LC - Least Concern

NatureServe

N5 - Secure
S4 - Apparently Secure

Minnesota

not listed

Northern leopard frog is a slim, medium-sized, widely recognized, spotted frog. It is the most common frog in Minnesota.

An outbreak of deformities in this species was discovered by school children in LeSueur, Minnesota, in 1995. The Minnesota Pollution Control Agency researched the problem from 1997 through 2000, when funding for the research was discontinued. The cause of the malformations remains unknown. According to the National Biological Information Infrastructure (NBII), research suggests that there is no single cause. The four major environmental factors contributing to the malformations are contaminants, nutritional deficiencies, parasites, and injuries from predators.

Adults are 2″ to 3½″ long at maturity. Males are smaller than females.

The back (dorsal surface) is smooth to moderately rough. Background color and spotting is variable. Most adults have 2 to 4 rows of black spots on a green background. Some have a greenish-brown or brown background, some have no dorsal spots, and some are brown with flecks of white, brown, or black between the spots. Juveniles may have few or no dorsal spots. The spots on all adults have a whitish or yellowish bordered. Prominent folds on each side of the back (dorsolateral) extend from the head to near the vent. The folds are light on top and dark at the base. They do not angle inward near the vent (anal opening). Males have a pair of inflatable vocal sacs on their shoulders. During breeding season these appear as areas of loose skin.

The belly is white or cream-colored.

There is a white stripe in the upper jaw. The ear covering (tympanum) is smaller than the eye.

The hind legs have dark horizontal bands. The inside of the thighs of the hind legs are pale with a greenish tint. The feet are webbed. Males have thick, dark thumb pads.

There are no recognized subspecies of Northern Leopard Frog but there are four color morphs. Most adults have 2 to 4 rows of black spots on a green background (green morph). Some adults have a greenish-brown or brown background (brown morph). The Burnsi morph is brown or green with no dorsal spots. The less common Kandiyohi morph has black mottling or additional black spotting between the spots.

Size

Total length: 2″ to 3½″

Voice

Amphibian Research and Monitoring Initiative (ARMI), Midwest Region

Frog and Toad Calls

A low pitched snore, lasting 2 to 4 seconds, and occasional clucks or croaks.

Similar Species

Pickerel Frog (Lithobates palustris) has a light tan background. The spots are squarish. The inside of the thighs of the hind legs are bright yellow. They are found only in trout streams in southeastern Minnesota.

Damp woodlands and grasslands, always near lakes, ponds, rivers, slow streams, marshes, or wetlands.

Behavior

Lifespan

5 to 7 years

Life Cycle

Adults breed in April and May. With the male still attached, the female lays a single round mass of between 300 and 6,500 black eggs, attached to vegetation just below the water surface. The eggs hatch in 1 to 2 months and tadpoles metamorphose into adults in about 50 days, depending on the weather. After metamorphosis they leave the pond to feed on dry land and to migrate. Mass migrations often occur after heavy rains.

Adults reach sexual maturity in 2 or 3 years. They hibernate usually in deep water that does not freeze completely. They live 5 to 7 years.

Tadpole Food

Algae, plant tissue, organic debris, and probably some small invertebrates

Adult Food

Insects, spiders, snails, earthworms, and other small terrestrial invertebrates.