Amphibians
Pickerel Frog
Lithobates palustris · also called marsh frog
The pickerel frog looks almost exactly like a leopard frog, and for a long time that was the point — it hides in plain sight among a common, heavily eaten species while carrying a defence the leopard frog lacks. Its skin is genuinely toxic, the only native North American frog for which that is true in any meaningful way.
Overview
Lithobates palustris lives across eastern North America in two broad regions, always near cool, clear water — springs, spring-fed streams, and bogs — moving out into wet meadows and fields to feed in summer. It is 5–8 cm long, tan with two rows of squarish dark spots and a hidden wash of yellow-orange under the thighs.
The toxin
Its skin secretions are noxious and toxic. Other frogs shut in a collecting bag with a pickerel frog have died; the secretion irritates human skin and eyes. Many snakes refuse it, so in habitats it shares with leopard frogs, the leopard frogs take most of the predation.
Telling it apart
Against the leopard frog, look for square, regularly spaced spots in two neat rows and the orange thigh flash — the leopard frog has rounder, scattered spots and pale hidden surfaces.
Status
The pickerel frog is Least Concern and stable, though it depends on cool clean water that is sensitive to pollution and warming.
Pickerel Frog: common questions
How poisonous is a pickerel frog?
It is the one native North American frog whose skin toxins are strong enough to have practical consequences, though it is nothing like a poison dart frog. The secretions are irritating rather than deadly to a person; handling one can leave skin red and itchy, and rubbing your eyes afterward stings sharply, so the advice is to wash your hands. The clearer demonstration of the toxin is what it does to other amphibians. Naturalists have long known not to put a pickerel frog in the same bag or bucket as other frogs and salamanders, because the confined secretions can sicken or kill them within hours. Pets that mouth a pickerel frog usually drool, retch, and learn to avoid them.
How do you tell a pickerel frog from a leopard frog?
They are similar tan frogs with dark spots and are often confused. The most reliable difference is the shape and arrangement of the spots. A pickerel frog has two lengthwise rows of fairly even, squarish or rectangular blotches down its back, looking almost as if they were stamped. A leopard frog has more numerous, rounder spots scattered in less regular rows. The other giveaway is colour under the legs. Flip the frog or watch it jump, and a pickerel frog shows a bright yellow or orange wash on the inner thighs and groin, while a northern leopard frog's hidden surfaces are whitish or pale green.
Why do snakes leave pickerel frogs alone?
The skin toxin makes the frog an unpleasant and sometimes harmful meal, and several snake species have evolved or learned to avoid it. Smooth green snakes and rough green snakes, which hunt frogs and insects, will generally not take a pickerel frog, and some water snakes reject them or release them after mouthing them. This gives the pickerel frog a real edge; in habitats it shares with leopard frogs, the leopard frogs bear the brunt of snake predation while the pickerel frogs are comparatively safe. Not every predator is deterred, though. Bullfrogs, larger frogs, and some birds and mammals still eat them.
Where does the name come from?
From fishing. Pickerel, which are small members of the pike family, were once commonly caught using live frogs as bait, and this species, being abundant along the cool clear streams and ponds where pickerel live and being easy to catch in numbers, was a frog anglers used. The association stuck as the common name. The scientific name, palustris, means of the marsh, which is only partly accurate; the pickerel frog spends much of the summer away from marshes, foraging in wet meadows, pastures, and old fields, and is sometimes called the marsh frog despite that.