The Carlisle Mosquito Online

Friday, October 10, 2008


Northern Leopard Frog (Rana pipiens)


This Northern Leopard Frog was photographed at Foss Farm on September 25, 2008. (Photo by Tom Brownrigg)

If you are walking along the edges of open fields at Foss Farm, Greenough and Great Meadows National Wildlife Refuge (or even your backyard) in Carlisle during the summer, and a frog suddenly jumps away as you approach, it’s probably a Northern Leopard Frog. Often you’ll see just a blur, but sometimes these frogs will allow you to approach very closely – if you move slowly. The Leopard Frog is usually green, but sometimes brown, with irregular rounded dark spots (with lighter borders) on the back. Adults range in size from two to four inches, with the female being larger than the male.

You might also see another similar-looking frog in Carlisle, the Pickerel Frog (Rana palustris). It too has dark spots on the back, but its spots are more rectangular, and run in two parallel rows down the back, like two brick walkways; the spots sometimes run together to form longer “bars.” Unlike the Leopard Frog, the inner surface of the hind leg of the Pickerel Frog is yellow or orange; but you’ll have to catch the frog to use this field mark. Both species are found in wet fields, but in my experience, the Leopard Frog generally strays farther from water.

When I was in high school, Leopard Frogs were used for dissections in biology class. The smell of formaldehyde still reminds me of these poor frogs and my dislike of dissection.

The Leopard Frog eats mostly insects, including beetles, lepidopteran (butterfly and moth) larvae, wasps, bugs, crickets, grasshoppers and ants. Other foods include spiders, sowbugs, worms, snails, and centipedes. Tom Tyning describes the Leopard Frog catching a prey item: “If the movement of an insect is within a few inches, the frog simply leans forward and with an incredibly rapid movement snaps it up with its tongue. Movements made by large beetles or worms that are farther away from the frog may cause it to step forward within grasping reach.”

Leopard Frogs breed in ponds, marshes, slow shallow streams and weedy lake inlets. Breeding occurs in March through May in New England. The female lays a mass of 4,000 to 6,000 eggs underwater which are fertilized externally by the male. Tadpoles transform into small frogs in August and September. Leopard Frogs overwinter in the mud at the bottom of ponds, marshes and streams, and sometimes in terrestrial caves. The natural lifespan of a Leopard Frog is at least three years.

The Northern Leopard Frog is relatively abundant in certain localized areas of Massachusetts, primarily along river floodplains. According to reference #4, however, its present status in the state is not well known and many scientists believe that local populations are in decline.

Richard Wolniewicz says: “Amphibians have often been referred to as the ‘canary in the coal mine’ as environmental indicators of pollution and other problems. Since they can easily absorb substances through their skin, they are highly susceptible to toxins, excess UV [ultraviolet] light, and other environmental hazards. This is why, when handling frogs, toads, and salamanders, it is important to make sure you do not have any insect repellent, sun tan lotion or any other chemicals on your hands that could potentially be absorbed by the animals.”


1. Conant, Roger. A Field Guide to Reptiles and Amphibians, Peterson Field Guides, Houghton Miflin Co., 1958.

2. Tyning, Thomas F. A Guide to Amphibians and Reptiles, Stokes Nature Guides, Little, Brown and Co. 1990.

3. DeGraaf, Richard M. and Yamasaki, Mariko. New England Wildlife: Habitat, Natural History, and Distribution, University Press of New England, 2001.

4. Kenny, Leo P. and Burne, Matthew R. A Field Guide to the Animals of Vernal Pools, Massachusetts Natural Heritage and Endangered Species Program & Vernal Pool Association, 2000.

5. Wolniewicz, Richard. Unfeathered Songsters: The Frogs & Toads of Massachusetts, Massachusetts Wildlife, Vol. LVI, No. 2, 2006. ∆


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