FOUND IN B.C.? Yes. They are widespread across the Lower Mainland, Sunshine Coast and Vancouver Island. There is also a population in the Creston Valley. No bullfrogs have yet been detected in the Columbia Shuswap Regional District.
They are generally pale to dark-green in colour on their backside, with a belly that is white to cream in colour. They have large tympanums (eardrums) behind their eyes and there is a skin fold around the tympanum. They also lack dorsolateral folds down the length of their back (common to other frog species) and they have dark bands on their hind legs. They are the largest frog in North America!
The Green frog is also invasive in B.C. While they also have quite a prominent tympanum, they also have dorsolateral folds that extend halfway down their back (which Bullfrogs do not have). When fully grown, Green frogs will not be as large as Bullfrogs: Green frogs will grow up to about 11 cm while Bullfrogs can reach up to 17 cm!
The Northern leopard frog is native to B.C. Similar colours to both the Green frog and Bullfrog but they have characteristic dark spots and their dorsolateral folds extend along the entire length of their back.
In B.C., their breeding season takes place from mid-June to mid-July once the air temperature warms up to about 20°C. Females will lay up to 20,000 eggs in shallow, vegetated water and these eggs form sheets near the surface of the water. In colder climates (like the B.C. interior), tadpoles will likely hibernate for the winter before metamorphosis the following spring. Male bullfrogs will have a bright yellow throat during the breeding season and have a unique mating call that has a deep and loud “jug o rum” sound.
Bullfrogs prefer areas with warm and slow-moving water like beaver ponds and they do prefer for this water source to be permanent and stable from year to year.
The American bullfrog is truly an opportunistic predator; it will eat anything that will fit in its mouth, eating both invertebrates and vertebrates, including birds, mice, turtles, snakes, fish and other frogs.
Introduction and Spread
The American bullfrog is native to eastern North America, including parts of Canada, like southern Ontario and Quebec, New Brunswick and Nova Scotia. They were first introduced to B.C. in the 1930’s for farming and consumption of their meaty legs. However, frog legs did not whet many appetites and frogs were released from farms.
In B.C., the presence of American bullfrogs in the Creston Valley was confirmed in 2016 and there has been significant efforts to reduce that population. Bullfrogs are also spread across the Lower Mainland, the Sunshine Coast and Vancouver Island.
Bullfrogs can travel overland up to 1 km and were able to naturally disperse from these farms along connected lakes and rivers. Their natural dispersal has been compounded with human-assisted pet releases from households and outdoor ponds.
The American bullfrog is on the list of “100 of the World’s Worst Invasive Alien Species” by the IUCN, the International Union for the Conservation of Nature – a list also highlighting species like zebra mussels, the Nile perch and water hyacinth. In fact, their trade and possession has been banned in some parts of the world, like Europe and Australia. Bullfrogs have been very successful in their new environments.
They are able to thrive because they are voracious and opportunistic predators, and so they can easily adapt to the food resources available which often involve feeding on native species like Red-legged frogs and Pacific tree frogs on Vancouver Island. There is even evidence that Bullfrogs may be immune to natural defenses of prey species, such as the toxicity of newts and stingers of bees or wasps. Their aggressive behaviour has led to declines of endangered amphibians. They do not have any natural predators in B.C. In their native range, they are normally kept in check by large snakes, birds, and even alligators. Female bullfrogs can lay up to 20,000 eggs per season. Many of our native frogs will only produce between 2,000-5,000 eggs and so they become outnumbered quickly. They carry and transmit diseases, like Chytrid fungus, to our at-risk native populations of amphibians, which are important players for cycling nutrients in aquatic ecosystems.
A study conducted by the U.S. Fish and Wildlife Service and others, found that removal of American bullfrogs is the necessary or preferred action in almost all cases for recovery of native frog species, like Northern leopard and Columbia spotted frogs, in the western U.S.
What Can We Do?
DON’T LET IT LOOSE: As humans, we are the number one vector of spread for
invasive species but we can also play an important role in stopping new invasions and infestations. Making slight changes to some of our behaviours is key to preventing and managing the spread of invasive species. The most important step you can take to prevent the spread of American bullfrogs is to be a responsible pet owner. This means that we understand and accept the responsibility of owning a pet and Don’t Let It Loose to the wild when the pet is longer wanted or can no longer be cared for. Most pets actually don’t survive in the wild as they do not have the proper adaptations to find food sources or detect predators. So before purchasing or adopting any pet, consider how you will take care of it for its entire lifespan. If you are longer able to care for a pet, contact rescue centres or other resources in your community to attempt to re-home your pet. Euthanization of the pet will be the last resort approach to dealing with a pet that can no longer be cared for, which is why it is really important to understand the long-term needs of the pet before ownership. This practice also applies to plants that we may have in our terrariums, aquariums or ponds as well.
For more information on Bullfrogs and other frogs, check out the BC Frog Watch Program.
For more information on amphibians in B.C., visit here.
Literature and Resources