|A large male American Bullfrog floats, calling in a pond. Note that the dorsolateral skin fold goes around the eardrum (tympanum) rather than going down the back.|
|A male Green Frog floats on a pond. Note that the dorsolateral fold of skin goes part way down the back.|
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 (ear drum) is larger than their eye. Female have eyes that are about the same size as their tympanums. These are all sexual differences their smaller Green Frog cousins also have.
|The larger male Bullfrog with its eardrum (tympanum) larger than its eye courts the smaller female who's tympanum is about the same size as the eye.|
Also unusual in frogs, the females will sometimes also 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. Indeed, I've several times heard the screaming and gone to investigate, interrupting a feeding snake in the process. In most species of frog or toads, only the males vocalize.
|A Bull Frog tadpole already developing its back legs.|
Once a female has chosen her suitor, she will lay a large floating mass of eggs numbering between 3,000-50,000 eggs. In less than 3 weeks, the tadpoles emerge. These tadpoles take 2 and sometimes 3 (up North) years to metamorphose into an adult. This again differs from most of our frogs which change over in a single growing season. The olive colored tadpoles can also grow to be our biggest. Some polliwogs can be up to 6" long. Although they typically eat algae or detritus just like other polliwogs, they are also unusual once again in occasionally scavenging meat and eating other tadpoles. They are distasteful to some fish as well which allows them to live in permanent ponds with them.
|Bull Frog tadpoles are the largest in North America and take the longest to develop (2-3 years) of all our native tadpoles.|
Bull Frogs will eat any smaller species there however. They have been outlawed for sale in some countries like England where they have become an invasive predator of small ponds. They have even been implicated in the demise of California's Red-legged Frog. Bull Frogs 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 who 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.
|A female Bull Frog.|