The pickerel frog (Lithobates palustris, formerly Rana palustris ) is a small North American frog, characterized by the appearance of seemingly "hand-drawn" squares on its dorsal surface.
The pickerel frog is a medium sized gray or tan frog marked with seven to twenty-one irregular rectangular dark brown spots which are oriented in two columns down its back. The distinctive rectangular spots of the pickerel frog may blend together to form a long rectangle along the back. All leopard frogs have circular spots. In addition, pickerel frogs have prominent dorsolateral ridges that are unbroken. Another important distinguishing mark is the orange or yellow flash pattern found on the inner surface of the hind legs of pickerel frogs. The frog must be picked up to examine this, as the legs cover the coloration otherwise. The plains leopard frog (Lithobates blairi ) exhibits this coloration as well, but the dorsolateral ridges are interrupted and inset medially in that species. The front toes of pickerel frogs are not webbed, a morphological characteristic for some frogs of the genus Rana and some frogs of the genus Lithobates. This allows pickerel frogs to be fit for terrestrial life.
The pickerel frog ranges in the west from much of Wisconsin, southeast Minnesota, eastern Iowa, through Missouri and down to eastern Texas. To the east they extend through northern Louisiana, most of Mississippi, northern Alabama, Georgia, and South Carolina to the coast. Their northern range extends into Canada in the southern reaches of Ontario, Quebec, New Brunswick, and Nova Scotia. The range is spotty through the midwestern states and a field guide should be obtained for the specifics on ranges in a particular area.
Pickerel frogs have varied habitats, the northern specimen prefers to live near cold, clear water. They prefer rocky ravines, bogs and meadow streams, but can be found around lakes and rivers that are heavily wooded. The southern specimen prefer warmer waters, like those of the Coastal Plain and floodplain swamps. They are seen most often along the edges of streams, lakes, rivers, and even flooded ditches. During the winter months they will hibernate under the silt and debris in their aquatic environments; they are usually only active from April to October. When feasible, this species utilizes caves for thermal refugia during the coldest months of the year. The pickerel frog is a trogloxene species meaning they occur in caves, but are unable to complete their life cycles there. Though they are most abundant in caves during the winter, they are active deep within caves at almost any time of year.
The pickerel frog's diet consists of ants, spiders, various bugs, beetles, sawfly larvae, and other invertebrates. In order to catch their prey pickerel frogs will often search grassy areas next to bodies of water.
Pickerel frogs prefer cool clear water. They breed in both temporary ponds and permanent ponds but appear to favor ponds with long to permanent hydroperiods. In Rhode Island specifically, pickerel frog tadpoles and eggmasses were found in permanent manmade rural ponds, farm ponds, and urban ponds surrounded by roads; all of the mentioned habitats were well-vegetated.
Pickerel frogs typically emerge from hibernation around mid April with the majority of the frogs arriving at breeding ponds by early May. At the ponds, pickerel frogs are usually observed in large groups in the water. Mating behavior is not much different from other ranids. The males initiate breeding by emitting their low pitched call; this call is usually so low pitched that it is often not heard during calling surveys. Males are known to call while submerged. Frogs reproduce using a method called Amplexus, a type of external fertilization; sometimes it will last more than a day or two, even after the female has deposited the eggs.
