American Bullfrog Impacts

These large frogs are a serious issue for native species. Because they are much larger than our native frogs, they will often outcompete them for resources such as food and breeding habitat. Besides competition for resources, American Bullfrogs are also very capable of eating other frogs, including members of their own species. The spread of diseases to native amphibians is also a concern. American Bullfrogs are known to carry, but not be affected by, the Chytrid fungus which can be a deadly pathogen to amphibians.

Both Bullfrogs and Green Frogs are native to eastern North America, in both Canada and the United States. With such a distance between B.C and their native range, the only way they could arrive here was via human transport. The first American Bullfrogs in B.C. were brought here to be farmed for frog legs and they have since spread well beyond their original location. Since their arrival, people have  continued to aid in their spread in several ways. Collecting and moving unknown wild frogs, using live tadpoles as bait, and releasing pets into the wild are some of the ways Bullfrogs and Green Frogs have been spread.  Bullfrogs are also able to travel over land and can thrive in human-disturbed habitats because they are very adaptable to changes in their environment. Once established in an area, populations can rapidly increase with just a few successful breeding seasons. A single female bullfrog can lay between 5,000 to 20,000 eggs per year.

Though the two species are closely related, Green Frogs are much smaller than American Bullfrogs and therefore less capable of eating native species of frogs. However, their presence in local environments still puts pressure on native species as they compete for space and resources. Overall, their impacts are thought to be less than American Bullfrogs though more research is needed to properly understand how they affect native ecosystems.

In the Fraser Valley the only native amphibian that is similar in size to an adult American Bullfrog is the Western Toad. However, these species have several features that can be used to tell them apart. Western Toads have warty, bumpy backs and sides while American Bullfrogs will always be smooth in these areas. In addition to this, Western Toads will usually have a cream or white coloured stripe running down the center of their backs. This stripe is located right where their spine would be and extends down the whole length of their torso. Bullfrogs will never have this stripe. Another feature that can be used to tell the two species apart is the size of the eardrum or “tympanum” which is located right behind the eye of a frog. Bullfrogs have large and very visible tympanums which have a fold of skin running behind them. While Western Toads also have these tympanums, they are not as obvious, and do not have the same fold of skin behind them.

Never transport, harm or kill an amphibian that appears to be an American Bullfrog without consulting an expert on identification.

While it may be tempting to act quickly to remove a Bullfrog from your area, we do not recommend it. Amphibian ID is tricky, and many times what appears to be a Bullfrog is actually a different species. It is always best to consult with an expert before doing anything. Submit your frog pictures to our Frog Finders program and we will ID the species for you with a reply to your submission.

In addition to this, removing single animals or even small numbers of adults is not an effective way of controlling Bullfrogs.  In fact, removing adults can have a negative effect as it helps more young bullfrogs survive to adulthood.

The best thing to do is to leave the frog alone. If you are concerned about local amphibians, enhancing habitat for them is a more effective way of dealing with the threat of Bullfrogs when compared to control measures.