Pickerel Frog Lithobates palustris

Description: Adult Morphology: A medium-sized, olive brown frog with large rectangular dorsal blotches. The blotches are neatly arranged in rows of two between the dorsolateral ridges. The underbelly of this frog is plain white in color and the legs are banded. Dorsolateral folds are present and are usually light orange or yellow. Pickerel frogs have a bright yellow wash around the groin region (similar to the gray treefrog complex).

Size: Pickerel frogs grow to around 3 in (50-70 mm) long.

Larvae: A large brownish tadpole that usually grows to around 3 in (60 mm) in length. The tailfin is heavily mottled.

Eggs: Females lay their eggs in globular masses of 3,000 or fewer eggs.

Similar Species: Pickerel frogs can be distinguished from the three leopard frogs in the state (Lithobates pipiens, L. sphenocephala, and L. blairi) fairly easily. Pickerel frogs have two rows of rectangular blotches in between their dorsolateral folds while leopard frogs have irregular, unorganized, round dorsal blotches. Pickerel frogs also have a brighter yellow wash around their groin than do leopard frogs.

Distribution: The pickerel frog is found through the eastern United States and parts of southern Canada; east from Texas in the south and Minnesota in the north.

Pickerel frogs are common in the creeks and springs of southeastern, west-central, and south-central Indiana. They have a patchy distribution in northern Indiana and are likely absent from much of central Indiana.

Activity: Pickerel frogs are most active from March to October but may also be active on mild days during the winter in and around caves.

Breeding Season: Pickerel frogs breed during April in most of Indiana though they may call during late March in southern Indiana when conditions are mild. After being deposited, the eggs hatch in a little over a week and the larvae transform during June or July.

Taxonomy: Pickerel frogs (Lithobates palustris) belong to the genus Lithobates and are in the family ranidae which is represented in Indiana by eight species. All Indiana ranids were formerly placed in the genus Rana, but have since been moved to the genus Lithobates. They have been placed in the nenirana species complex and their closest relatives in the state are crawfish frogs (L. areolatus). Despite significant differences in adult size and natural history, the two frogs have a similar "snore"-like call, relatively abbreviated spring breeding seasons, and both species inhabit underground refugia (crayfish burrows for L. areolatus and caves for L. palustris). In southeastern Indiana, the two frogs have been found breeding in the same wetlands.

Ecology: Habitat: In Indiana, this is a species of cool-clear, often spring-fed riparian environs. Pickerel frogs are often found in caves and springs in southern Indiana and they are also associated with clean flowing streams and shaded ravines. This species is the only North American frog known to routinely use caves in large numbers for hibernation. They are often found under rocks and logs near the water's edge, but can also be found crossing roads on rainy nights or actively moving around in or just outside of caves. Pickerel frogs may be encountered in rock crevices in caves and along moist rock faces.

Diet: Pickerel frogs feed on a variety of terrestrial invertebrates.

Reproduction and Life History: In Indiana, pickerel frogs breed primarily in upland, ephemeral wetlands. It has also been suggested that they may breed in cave pools in some locations (based on calling heard from inside caves).

Call: The call is a low croak or snore lasting a couple seconds. Unlike other frogs, the pickerel frog will often call underwater.

Conservation: Pickerel frogs are abundant where karst topography is present, but elsewhere are more localized. Few threats are known to Indiana populations, but a Missouri study found that pickerel frogs avoided areas where invasive amur honeysuckle bushes were dense (this is a common invasive plant in Indiana). Despite being most often associated with forests in Indiana, pickerel frogs do not appear to respond negatively to clear-cutting and other timber harvesting practices.

Poisonous: Pickerel frogs are known to have mildly toxic skin secretions which make them unpalatable to some predators. This is not a serious concern for humans, but it is always best to wash your hands after handling this species (and other amphibians) and try to avoid housing pickerel frogs with other animals in captivity.

Literature

Conant, R. and J. T . Collins. 1998. Reptiles and Amphibians of Eastern and Central North America. Third Edition, Expanded. Houghton Mifflin, New York, New York.

Engbrecht, N. E., S. J. Lannoo, J. O. Whitaker, and M. J. Lannoo. 2011. Comparative Morphometrics in Ranid Frogs (Subgenus Nenirana): Are Apomorphic Elongation and a Blunt Snout Responses to Small-bore Burrow Dwelling in Crawfish Frogs (Lithobates areolatus)?. Copeia 2:285-295.

Formanowicz, D. R. Jr. and E. D. Brodie. 1979. Palatability and Antipredator Behavior of Selected Rana to the Shrew Blarina. American Midland Naturalist 101.2:456-458.

Hillis, D. M. and T. P. Wilcox. 2005. Phylogeny of the New World True Frogs (Rana). Molecular Phylogenetics and Evolution 34.2:299-314.

Hoffman, A. and S. Shepard 2014. Lithobates palustris. Pickerel Frog. Geographic distribution (Putnam County). Herpetological Review 45:87-88.

Minton, S. A. Jr. 2001. Amphibians and Reptiles of Indiana. Indiana Academy of Science, Indianapolis, IN.

Pasachnik, S. A. 2003. Lithobates palustris. Pickerel Frog. Geographic distribution. Herpetological Review 34.4:382.

Pierson, T. P. 2012. Lithobates palustris. Pickerel Frog. Geographic distribution. Herpetological Review 43.2:300.

Popescu, V. D., D. A. Patrick, M. L. Hunter Jr., and A. J. K. Calhoun. 2012. The Role of Forest Harvesting and Subsequent Vegetative Regrowth in Determining Patterns of Amphibian Habitat Use. Forest Ecology and Management 270:163-174.

Resetarits, W. J. Jr. 1986. Ecology of Cave Use by the Frog, Rana palustris. American Midland Naturalist 116.2:256-266.

Watling, J. I., C. R. Hickman, and J. L. Orrock. 2011. Invasive Shrub Alters Native Forest Amphibian Communities. Biological Conservation 144.11:2597-2601.

Distribution Map
Distribution map of Pickerel Frog (Lithobates palustris)
Photographs