Bullfrog (Rana catesbeiana)
Compare the size of a Bullfrog (top) with an adult Leopard Frog (bottom).
Description: Bullfrogs are generally brown or green, occasionally with black mottling over the back and legs. Unlike other frogs of the same genus (Rana), they have no dorsolateral folds. Not all individuals are as dark as the ones pictured above. They are large frogs that can reach adult lengths of 8 inches (snout to rump).
Habitat/Ecology: Bullfrogs prefer large permanent bodies of water that do not dry out or freeze completely. They generally do not stray far from a water source of some kind. Bullfrogs are said to consume a wide variety of prey, including insects, fish, other frogs, small snakes, mammals, and birds. As juveniles, these frogs probably fall victim to many predators, however, as adults, their size probably helps them avoid predation.
Remarks: Male Bullfrogs usually begin calling later than other frogs in the area (mid-June through mid-July). Their call is a deep "Ba-ruum" sound that is very distinct. Bullfrogs will sometimes release a high-pitched distress call if captured or startled. In some areas (especially the western U.S.), Bullfrogs are considered invasive because of their voracious appetites and ability to eat many kinds of prey, while their own larva are reported to be distasteful to many predators. Therefore, they will frequently eliminate many other species, yet multiply at alarmingly fast rates until they are the dominant and most prolific predator in a wetland. Bullfrogs are not very common in the La Crosse area, but have been reported.
I have found Bullfrogs in only one area of La Crosse, a very deep golf-course pond located on the south side of town. It is interesting to note that within this pond, no other amphibians were witnessed, yet several species of large fish (bass) were observed. In my opinion, this may lend credence to the reports that Bullfrog tadpoles are distasteful to some fish predators. I have also heard them calling in a lowland forest-swamp located near Rush Creek in Crawford County.
Ever wonder why frogs are so hard to see in the wild? Check out this Bullfrog. Can you see him? If frogs remain still, their coloration is such that they can blend in with their surroundings very well. This helps them avoid being eaten by predators.