Creature Feature: Pickerel Frog

Pickerel Frog

Lithobates palustris

Cool fact: The square markings on their back vary from 7-21, depending on geographic regions.

The pickerel frog is a slender North American species, gray or brown in color, characterized by two parallel rows of imperfectly shaped dark brown squares on its back. These squares are located between two prominent unbroken ridges (dorsolateral folds) that extend from behind the eyes to the groin; there is an orange-yellow flash pattern on the underside of the hind legs. Pickerel frogs weigh up to 0.12oz and are 2-3½” long. Depending on which website you read, they are described as small, medium, AND large, so maybe the size is determined by the eye of the beholder!

People often have a hard time identifying pickerel vs leopard frogs because of their similarities, but they do have distinct differences. Leopard frogs are a little larger at 4½” and are green or brown. They typically have circular spots, not squares, with a lighter colored border.

The pickerel frog is found in Canada from Nova Scotia and New Brunswick west to Quebec and Ontario, although has been sighted in Newfoundland and Labrador as well. Its range is extensive in the eastern US, from New England south to Georgia and west to Minnesota, Iowa, and Missouri, along the Mississippi Drainage to the Gulf Coast in eastern Texas; however, their midwestern range is spotty.

Pickerel frogs have mixed habitats: the northern populations prefer to live near cold, clear water, e.g., spring-fed ponds, as well as bogs, marshes, and shallow streams; they can also be found around lakes and rivers in heavily wooded areas. Pickerel frogs in the southern portion of their range prefer warmer waters and floodplain swamps; they’re often found along the edges of streams, lakes, rivers, and even flooded ditches, wet fields, and damp grass of lawns.

Their diet includes a wide variety of land and aquatic invertebrates, such as ants, beetles, caterpillars, spiders, larvae, worms, snails, and crayfish. They’re usually active from April – October, and during the winter months, hibernate under the muddy silt and debris in their aquatic environments. Pickerel frogs use caves and rocky ravines for refuge when temperatures drop as well as during hot summers.

Pickerel frogs are sexually dimorphic, with females being larger and darker than males. Other than mating behavior, the males and females are virtually identical; they begin to reproduce at two years of age. When air temperatures rise above 50°F, they become more active and breed in temporary bodies of water, such as vernal pools, which lack predatory fish, and permanent ponds. Frogs reproduce by external fertilization, and the females lay masses of 2,000 – 3,000 eggs, usually in well-vegetated areas. Eggs are spherical and multicolored (dark brown on top, cream colored on the bottom); based on temperature, eggs hatch in 11-21 days.The tadpole stage lasts about three months; they feed on algae and aquatic organic matter. When small, they’re yellow to yellowish brown, but as they grow the color changes to olive green and eventually gray brown on top, cream-colored underneath. The next stage is the froglet, when the hind legs grow, followed by the front legs, and lung development to replace gills. It is considered an adult frog when the tail is fully absorbed, the mouth widens, and the digestive tract shortens for a meat diet.

As a means of defense, pickerel frogs emit skin secretions, which are irritating to people and toxic to some predators; most mammals, birds, snakes, and other frogs will leave the pickerel frog alone. However, green frogs, bullfrogs, and water and garter snakes, are unphased by the poison.

As with most other species, pickerel frogs face threats of habitat loss with residential and commercial development, farming, and clearcutting. Their populations are listed as “Least Concern” by the IUCN (International Union for Conservation of Nature) and “secure” in Maine. There is always more to learn about their distribution and ecology, so please consider sharing your sightings and photos as part of the Maine Amphibian & Reptile Atlas Project (MARAP).

More “Cool Facts“

• The pickerel frog is the only poisonous frog native to North America.
• They don’t have webbed toes, allowing them to spend most of their time on land.
• The square markings on their back vary from 7-21, depending on geographic regions.
• During mating, the males get swollen thumbs and sing to the females. Their calls are quiet, long, drawn-out snores, often so low they’re not easily heard by humans. Males are even known to call while submerged.
• Pickerel frogs are a trogloxene species, meaning they live in caves; however, they’re unable to complete their life cycles in that environment.

—by Jayne Winters

Resources:

• https://www.maine.gov/ifw/fish-wildlife/wildlife/species-information/reptiles-amphibians/pickerel-frog.html
• https://critter.science/the-pickerel-frog/
• https://en.wikipedia.org/wiki/Pickerel_frog
• http://www.vernalpools.me/the-frogs-of-maines-vernal-pools/
• https://www.inaturalist.org/taxa/66002-Lithobates-palustris
• https://articles.hepper.com/pickerel-frog-vs-leopard-frog/