Mink frog

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The mink frog (Lithobates septentrionalis) is a small frog found in the United States and Canada. It’s named for its scent, which some people compare to mink (others say it smells like rotting onions). It’s also called the north frog.

Looks and size: Mink frogs grow to about 1.9–3.0 inches (4.8–7.6 cm). The back is green with darker green or brown blotches, and the belly is cream to white. Males usually have a bright yellow throat, while females have a white throat. The males’ eardrums (tympanum) are larger than their eyes; for females, the tympanum is about the same size or smaller than the eye. They have a pale underside and bright green lips.

Habitat and range: These frogs spend a lot of time in the water, living among vegetation like lily pads in ponds, swamps, and streams in wooded areas. They are found in many parts of the United States (including Minnesota, New Hampshire, Wisconsin, Michigan, Maine, Vermont, and New York) and in several Canadian provinces (Nova Scotia, New Brunswick, Newfoundland and Labrador, Quebec, Ontario, and Manitoba). They tend to occur at the northern edge of where frogs live in North America, and some southern populations may have disappeared in the past century.

What they eat: Mink frogs eat a variety of invertebrates such as spiders, snails, beetles, and other small creatures. Tadpoles mainly eat algae and decaying plant matter.

Breeding and life cycle: Breeding takes place in late spring to early summer. The frogs prefer cold, well-oxygenated wetlands. Males call at night from the water’s surface or from floating vegetation to attract females. Females can lay between about 500 and 4,000 eggs at a time, usually in deep water near floating plants. The eggs hatch within days, and the tadpoles stay in the larval stage for about a year before becoming froglets. Males reach maturity in one year; females take about two years.

Predators and threats: Eggs and embryos are eaten by eastern newts. Tadpoles can be eaten by eastern tiger salamander larvae, five-spined sticklebacks, giant water bugs, and North American leeches. Adults are prey for American bullfrogs (a major threat), as well as green frogs, eastern garter snakes, great blue herons, wood ducks, spruce grouse, and raccoons. In recent years, mink frog populations have been declining, and the southern edge of their range is shrinking.

Health concerns: A 1999 study reported deformities in mink frogs, including missing or extra limbs and other limb abnormalities. The researchers linked these deformities to exposure to certain chemicals called retinoids, but more research is needed to confirm the cause.