Leopard frogs are from 5 to 11.1 cm long. They are green or greenish-brown dorsally, with round, brown spots arranged on their back, sides, and legs. These spots usually have a whitish or yellow border. There is a distinct, white dorso-lateral fold along the length of the back extending from each eye. A white line runs on either side of the mouth, from the nose to the shoulder. The underside is white or greenish white. (Harding, 1997)
As with most frogs, males are smaller than females. Males have thickened thumb pads and paired vocal sacs that inflate over their shoulders as they call. (Harding, 1997)
Tadpoles are greenish or brown, with yellow or black speckles frequently visible. The belly is white and somewhat transparent, with the intestinal coils visible through the skin. Tadpoles reach a maximum size of 8.4 cm. (Harding, 1997)
Leopard frogs are native to the Nearctic region. They are found throughout much of North America, from as far north as the Hudson Bay, along the eastern seaboard to northern Virginia and west to British Columbia, eastern Washington, and Oregon. The western part of the range extends as far south as New Mexico, Arizona, Colorado, Utah, and portions of California and Nevada. Populations in the west are fragmented and some are declining.
Leopard frogs are found in a wide variety of habitats, including marshlands, brushlands, and forests. They prefer the presence of permanent, slow-moving water, including aquatic vegetation, but can be found in agricultural areas and on golf courses. Leopard frogs are well-adapted to cold and can be found at elevations up to 3,350 meters. They are commonly known as meadow frogs or grass frogs because they tend to stray far from the water when it is not breeding season. They prefer open areas to woods. (Fryer and Tunstall, 2001)
The small, black and white eggs are laid in clusters and attached to submerged vegetation. When Leopard frog eggs are laid they are roughly 1.7 mm in diameter, but swell to 5 mm when they come in contact with water. Clusters of eggs may act to increase heat absorption by the mass or to protect some eggs from predation. Hatching occurs after 1 to 3 weeks, varying with water temperature, and metamorphosis occurs after 70 to 110 days as a tadpole. Froglets are 2 to 3 cm long at metamorphosis. (Harding, 1997)
Leopard frogs gather at communal breeding ponds in the spring, where males call to attract females. If successful, a male will hold a female in "amplexus", using his specialized thumbs, and fertilize her eggs as they leave her body. Mating pairs may move to an area of the pond where other pairs have laid their eggs before they add their own. (Harding, 1997)
Mating occurs from March to June, but peaks in April. Females lay from 300 to 6500 eggs in globular clusters in breeding ponds. After metamorphosis, sexual maturity is reached in 1 to 3 years, depending on conditions. (Harding, 1997)
Most parental investment occurs prior to fertilization. Females will provide the eggs with nourishment to grow and will attempt to attach them to underwater vegetation in a tight cluster, after which the eggs are left to develop on their own. (Fryer and Tunstall, 2001; Harding, 1997)
Leopard frogs may live up to 9 years in the wild, although very few leopard frogs will live for this long. Most mortality occurs as a tadpole or newly transformed froglet, when as many as 95% will die. (Harding, 1997)
Leopard frogs are solitary outside of the breeding season, but tolerant of other leopard frogs. They do not establish territories, except in the breeding pond, where males will establish small calling territories. They are most active at night during the breeding season and most active during the day when foraging. Leopard frogs migrate to breeding ponds in the spring and may disperse away from water during the summer to forage in meadows and grasslands. They obtain water by absorbing dew from plants during this time. In the winter they travel back to their "home" pond, a permanent body of water, and overwinter in the mud and organic debris at the bottom. (Harding, 1997)
Leopard frogs do not establish home ranges.
Leopard frogs use calls to attract mates during breeding season. Male advertisement calls are described as sounding like a low, rumbling snore with occasional clicks and croaks. Males and non-receptive females will give a chuckle-like "release" call when clasped by a male hoping to mate. Outside of breeding season there is little need to communicate with conspecifics. They may scream loudly when they have been seized by a predator or squawk as they jump to avoid a predator. Frogs in general are quite sensitive to movement in detecting prey visually. (Fryer and Tunstall, 2001; Harding, 1997)
Leopard frog tadpoles are mainly herbivorous, eating algae, diatoms, and small animal matter filtered from the water or scraped from surfaces. Once they metamorphose into a frog, leopard frogs eat terrestrial invertebrates, including spiders, insects and their larvae, slugs, snails, and earthworms. Large adults may also eat small vertebrates, such as smaller frogs (spring peepers, Pseudacris crucifer, and chorus frogs, Pseudacris triseriata). (Fryer and Tunstall, 2001; Harding, 1997)
Many predators take advantage of leopard frog prey. Adults are taken by fish (bass and pike), herons, green frogs, bullfrogs, garter snakes, water snakes, hawks, gulls, raccoons, foxes, mink, and otters, as well as other predators. Eggs are eaten by leeches, newts, and turtles. Tadpoles are preyed on by diving beetles, giant water bugs, dragongfly larvae, and most of the vertebrates that prey on adults. (Harding, 1997)
Leopard frogs do not have distasteful skin secretions, they rely on their quick responses to leap into the water or make erratic hops to escape capture. Their coloration makes them blend into their surroundings when in vegetation. In areas where they co-occur with pickerel frogs (Lithobates palustris), leopard frogs have spots that are squarish, like those of pickerel frogs. Because pickerel frogs have distasteful skin secretions, it is thought that perhaps leopard frogs in those areas are mimicing pickerel frogs to avoid predation. (Harding, 1997)
Leopard frogs are important predators of their invertebrate prey and eggs and adults can act as important food sources for small to medium-sized predators.
There are no negative impacts of leopard frogs on humans.
Leopard frogs are eaten by humans (frog legs), and are used as test subjects in many biomedical research projects, both as adults and as tadpoles. Leopard frogs are also taken for use in biology classrooms. Leopard frogs are valuable members of the ecosystems in which they live, controlling invertebrate pests and acting as an important food source to larger predators. They may also act as indicator species for environmental health and water quality. (Fryer and Tunstall, 2001; Harding, 1997)
Leopard frogs were once common and widespread throughout much of North America. However, some populations have experienced serious declines. In the Great Lakes area, leopard frogs were abundant through the 1970's, after which they experienced a population decline. They remain uncommon in this area, although they can be locally abundant. In the western states, the status of many leopard frog populations remains unstudied. Leopard frogs, along with many other frog species, are at risk of poisoning by pesticides, including atrazine and organochlorines, herbicides, such as nitrates, and other water contaminants. Atrazine has been demonstrated to induce reproductive abnormalities in frogs at levels lower than are found in most North American water sources. Infectious diseases may also pose a significant threat to leopard frogs. Susceptibility to infectious diseases may be exacerbated by water acidification, lowering leopard frog immune responses. Introduced species, including bullfrogs (Lithobates catesbeianus) and common carp (Cyprinus carpio), may be contributing to declining numbers of leopard frogs as well, as they prey extensively on young and adults. Leopard frogs are extensively collected in some areas for use in classrooms, laboratories, and as bait, devastating local populations. Finally, leopard frogs, and other freshwater aquatic species, are at risk because of extensive freshwater habitat loss in North America, estimated at 53% of wetlands lost in the 1980's since 1780. (Fryer and Tunstall, 2001; Harding, 1997)
"Burnsi" morph leopard frogs are rare color variants that are uniformly brownish green on their back and legs, lacking the spots found on most individuals.
Tanya Dewey (author), Animal Diversity Web.
Fryer, B., T. Tunstall. 2001. "Rana pipiens" (On-line). Amphibiaweb. Accessed July 28, 2005 at http://elib.cs.berkeley.edu/cgi-bin/amphib_query?query_src=aw_search_index&where-genus=Rana&where-species=pipiens&rel-genus=equals&rel-species=equals.
Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan: The University of Michigan Press.