The American Bullfrog in Arlington

Published on May 21, 2015

The American bullfrog (Lithobates, formerly Rana, catesbeianus) is the largest native frog in North America. It can grow to eight inches (203mm) and has traits that make it quite different from Arlington’s other frogs besides its size. It is quite variable in color, particularly when young and often confused with its smaller and much more common cousin, the green frog (Lithobates clamitans). The skin fold that begins behind its eye (the dorsolateral fold) goes around the eye rather than down the back as in the green frog. Learn more on the green frog here.

Unlike other North American frogs where the female, in order to be able to carry more eggs, is larger than the male, just the opposite is true of bullfrogs. The males are bigger, so when having territorial disputes, the larger males can force or bully the smaller ones away. The larger males have thus have greater mating success.

Males are quite easy to tell from females once they are adults. Not only are they bigger and have a yellowish throat during the breeding season, but their tympanum (eardrum) is larger than their eye. Females have eyes that are about the same size as their tympanums. These are all sexual differences their smaller green frog cousins also have.

Right now, males are now giving their “jug-o-rum” calls in Arlington’s permanent ponds. You can hear and see them do this in this video clip from the Capital Naturalist YouTube Channel.

Also unusual in frogs, the females will sometimes call, though this is normally the scream both sexes may give if they are caught by a predator. Some suspect that this release call attracts an even larger predator that might break up the attack and allow the frog to escape in the scuffle. I’ve actually heard the screaming several times and gone to investigate, interrupting a feeding snake in the process. In most species of frog or toads, only the males vocalize.

Once a female has chosen her suitor, she will lay a large floating mass of eggs – between 3,000-50,000. In less than three weeks, the tadpoles (also known as pollywogs) emerge. These tadpoles take two and sometimes three (up North) years to metamorphose into an adult. This again differs from most of our frogs, which grow into adult’s within a single season. The olive colored bullfrog tadpoles can also grow to be Arlington’s biggest tadpoles. Some polliwogs can be up to six inches long. Although they typically eat algae or detritus just like other polliwogs, they do rarely sometimes for meat and eat other tadpoles. Bullfrog tadpoles are distasteful to some fish, which allows them to live in permanent ponds alongside them.

Bullfrogs are notorious for eating anything smaller than themselves, including each other. I’ve seen them eat small mice, frogs and even snakes. Once, while watching a Red-winged Blackbird land next to the water during a children’s nature outing, a large bullfrog grabbed it and fought it for a while. Eventually, the ruffled bird got away. This voracious trait has resulted in some local extinctions of small animals.

Bullfrogs are the most commercially available frog tadpoles because they take so long to change into adults and can be kept with small fish in aquarium pet stores. For this reason, they are most frequently bought for release into home ponds. Because they will eat any smaller species, they have been outlawed for sale in some countries like England where they have been become an invasive predator of small ponds. They have even been implicated in the demise of California’s red-legged frog. Bullfrogs from Maryland were taken to California for their edible legs and for frog jumping contests, like that at the famous Calaveras Fair. Now they pose a threat to the smaller red-legged frogs which were already in trouble due to habitat destruction. It is important to realize that being native does not mean they belong everywhere, as that can upset the natural balance.

Bullfrogs, if they survive being eaten by each other, snakes, humans or the numerous other creatures who consume them, can live 15 years. It takes a male 1-2 years to reach sexual maturity (2-3 for a female). Their Latin name was given to them in honor of the great American naturalist Mark Catesby.

I truly appreciate these large frogs and their calls. Many times I’ve put aside my fishing rod or stopped what I was doing to try and sneak up on them and see what they are up to. I’ve been rewarded by many observations of them eating or being eaten. Luckily, these are tough amphibians that can survive in less than ideal conditions, including farm ponds and park lakes. But they do not belong in every body of water because of their great size and appetites. Now that you know a bit more about them, you hopefully can appreciate them more as well.