Mink Frog
Rana septentrionalis

by Jeff LeClere

Status

Mink frogs have no status in Minnesota.

Description

The mink frog is a medium sized frog (about 3 inches body length). The mink frog is green with black spots or mottling. Sometimes, the dark pigment is very invasive; green may only be seen on the head and lips. Usually, however, the dark pigment forms a network or reticulated pattern on the back. The belly is white or yellowish with or without gray markings. The dorsolateral ridges may be present, reduced, or absent. The tympanum of males is larger than the eye; those of females are the same size or slightly smaller than the eye. The mink frog differs from the green frog in that the mink frog has extensive black pigment (usually mixed with green pigment) on the back, full webbing of hind feet, eyes positioned slightly on top of the head, a minklike or rotten onion smell. Mink frogs are not found south of the Twin Cities.

Subspecies

There are no subspecies of the mink frog, Rana septentrionalis.

Range

The mink frog is basically found in the northern half of Minnesota, although records are absent from much of western Minnesota, even in the north. Mink frogs are not found south or west of the Twin Cities (Hennepin and Ramsey Counties).

Habitat

The mink frog favors permanent wetlands like lakes, ponds, deeper bogs, and slower portions of rivers. They stay very close to these waters in more open areas, but they may move a short distance if the wetland is surrounded by damp, heavy forest; especially if there are numerous bogs and potholes nearby.

Habits

Mink frogs emerge from hibernation in late April or early May (especially in the north) but they do not breed until late May into August. Males vocalize while floating. They make a "knock, knock, knock" call or sometimes a creaking sound like an old rocking chair. Females lay masses of eggs that number 3,000 or 4,000. Tadpoles metamorphose in about three months, and some not until their second year. Mink frogs are probably the most aquatic of Minnesota's frogs, rarely leaving the water except for extended periods of high humidity or during heavy rains. I have seen the most specimens active on the roads in mid to late summer. Usually they remain in the wetland, away from shore sitting on lily pads or masses of aquatic vegetation. They hibernate underwater in their home lake, pond, or river.

Food

Mink frogs usually eat aquatic or flying insects, earthworms (when on land) and other invertebrates.