SOME FROGS ARE OUT OF PLACE
By Whit Gibbons
In the United States, the largest frog is the American bullfrog. The largest one in the tree frog family is the Cuban tree frog. In some situations, both qualify as bad boys of the frog world because they have shown up where they do not belong.
Cuban tree frogs are native to Cuba, the Bahamas and the Cayman Islands. Elsewhere they can be an invasive species of the worst kind, competing with and cannibalizing other frogs. The maximum size for U.S. tree frogs is less than 3 inches long, whereas the largest Cuban tree frogs are over 5 inches. They can readily overpower the smaller native tree frogs. Cuban tree frogs have also been documented to eat lizards and small snakes.
These wrongdoers from the tropical islands were first reported in Florida in 1931, probably arriving as stowaways on ships traveling between Miami and Havana or other Caribbean ports. Without competition from other frogs and with no natural predators in the Florida Keys, they expanded their geographic range. Today they are established throughout the Florida peninsula. They have been sighted recently in Savannah, Houston and other warm weather cities. They probably arrived in these new homes via horticultural shipments, motor homes or boats on trailers. When they become entrenched in a location, it means bad news for native wildlife. Florida is already experiencing declines in its native frogs, disappearances in many localities being attributed in part to the encroachment by Cuban tree frogs.
As if the loss of our native wildlife were not bad enough, these huge tree frogs have noxious skin secretions presumed to be repellent to native snakes, birds and mammals that might otherwise prey on them and keep them in check. The skin mucus is a powerful irritant known to cause allergic responses and even asthma attacks in some people. On a field trip in Florida, a Cuban tree frog we had caught jumped out of someone’s hand and landed smack in my son’s eye. He was unable to see out of that eye for several painful hours. They have big toe pads that allow them to climb up any tree or wall, and they often create a nuisance when “they invade toilets ... clog drains” or enter “power boxes and cause power outages,” according to Steve Johnson at the University of Florida.
Meanwhile, the American bullfrog is a mainstay of swamps, rivers, lakes and other wetlands. These iconic frogs are native throughout the eastern United States (except for southern Florida) into southern Canada. Bullfrogs will eat almost any animal that doesn’t eat them first. I recently received a photo of one sitting on the side of an outdoor pool with a full-grown bird believed to be a tufted titmouse in its mouth. In the eastern United States, bullfrogs are kept under control by an abundance of native predators, including water snakes, raccoons and alligators. Problems arise when bullfrogs are introduced to regions where they do not have a suite of predators for population control. In western states they have acquired an unfavorable reputation.
Several endangered species of frogs and salamanders have reportedly been eaten by introduced bullfrogs in California and Arizona. Although data are often difficult to document with certainty, bullfrogs have been implicated in regional declines of native amphibians and fish in other countries where they have been introduced, including Germany, Italy and France. Bullfrogs also have the potential for spreading parasites and diseases to native amphibians that have no natural defenses against them, as well as competing with native frogs for food resources.
The introduction of bullfrogs into other countries or states outside their native range can lead to ecological disaster, a problem perceived serious enough to warrant controls to limit their introduction into areas where they are not native. The use of legal roadblocks to limit free transport, sale or even ownership of a wild species is unfortunate. But even more unfortunate are the consequences of the improper introduction of a species in places where it does not belong.
Dr. Whit Gibbons is Professor Emeritus of Ecology, University of Georgia, and former Head of the Environmental Outreach and Education program at the Savannah River Ecology Laboratory (SREL). He currently serves on ARC's Board of Directors.