Wednesday, July 24, 2024

Leopard frogs have distinct, pale ridges along both sides of the back. (Photo: Alan W. Wells)

The northern leopard frog (Lithobates pipiens or Rana pipiens) is medium-sized with three rows of dark spots, each circled by a white or green ring. The spots look similar to those of a leopard (hence the name leopard frog). Leopard frogs use multiple habitats: They breed in shallow marshy wetlands, hunt in damp, grassy meadowlands and overwinter in deep ponds.

Leopard frogs, like all amphibians, need water or a damp environment to survive. Although adults have lungs, they also breathe and absorb water through their skin. They have special skin glands that transport water, oxygen and carbon dioxide in and out of their bodies. If their skin dries out, they cannot absorb oxygen. They are, therefore, very sensitive to the drying effects of the sun and wind. Amphibians are the first creatures to die when habitats are disturbed or contaminated. More than half of all frog species are in danger of extinction.

Each leopard frog spot is surrounded by a lighter halo or border. (Photo: Teá Montagna)

In the winter, leopard frogs dig a hole in the bottom of a pond or other body of water. There they lie dormant, breathing oxygen through their skin, until the water warms in mid- to late March. The Massachusetts breeding season begins in April. At this time, the frogs migrate from ponds to shallow-water breeding sites in meadows or swamps. At night, during warm spring rains, these frogs (and many other amphibians, such as wood frogs and salamanders) travel overland (including across roads) to reach their breeding sites. The frogs choose still, permanent water exposed to the sun so their eggs can develop.

Many species, including great blue herons, prey on frogs. (Photo: Richard George)

When daytime temperatures reach 50 degrees Fahrenheit, the males puff out their throats and begin trilling and croaking for females. As the weather grows increasingly warm, they become more and more vocal. Many males croaking together may make up a chorus that lasts for days.

The females soon arrive and select their mates. Once paired, the female swims around while the male clings to her back using special thumbs for grasping. In two or three days, the female lays her eggs; the male fertilizes them as she releases them into the water. The eggs are in a protective jellylike mass that contains up to 6,000 eggs. The mass is usually attached to vegetation just below the water’s surface.

Leopard frogs can be green or light brown. (Photo: Judy Asarkof)

In a week to 10 days, tadpoles hatch, breathing through gills. They are mostly vegetarians that eat algae and other plant matter. Slowly the tadpoles grow, losing their tail and developing limbs. By July or August, they have become small carnivorous frogs that can breathe air using lungs. These small frogs gather together near the edges of the wetlands, mostly hidden by vegetation. Frogs do not drink water like we do. Instead, they absorb water through the skin on the belly and thighs. This region of their skin is called the drinking patch.

A leopard frog in Arlington’s Great Meadows. (Photo: Ann Schlesinger)

During late summer and early fall, the adult and juvenile frogs return to their overwintering sites. There they forage around the edges of the pond until winter’s cold temperatures arrive. Then they head for deep water, where each frog digs an overwintering spot.

Leopard frogs eat almost anything that crosses their path and will fit in their mouth, including insects, spiders, snails and crustaceans. They are important insect predators. The young frogs mature in two years and live for about five.

A leopard frog in Topsfield. (Photo: Brian Rusnica)

Across the country, since the 1970s, northern leopard frog populations have declined dramatically. Leopard frog populations in Massachusetts appear to be declining as well. Habitat fragmentation and loss of wetlands due to development is a primary reason. Filling in of vernal pools where these frogs stop during their migrations also contributes. (Vernal pools form in winter in low-lying depressions in forests. Snowmelt and spring rains fill the pools, which are a magnet for all kinds of water-seeking amphibians.) Pesticides, deicing salts and fertilizers contaminate frog wetlands and make the water chemistry unsuitable. Automobile traffic kills frogs during their nighttime migrations across roads. And if these things were not enough, pathogens introduced from the commercial pet trade also kill these frogs.

Leopard frogs are 2 to 5 inches. (Photo: Meghan Sullivan)

Four hundred years ago, the Japanese poet Takarai Kikaku said:

Come come! Come Out!
From bogs old frogs command the dark
and look . . . the stars

Let’s hope these wonderful creatures still will be around to write about in another 400 years.

Leopard frogs have a white line that runs from the nose to the shoulder. (Photo: Ann Schlesinger)

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.

This post was updated April 8, 2023, to correct a photo credit.