Vectors of spread:
American Bullfrogs are easily identifiable by their size, as they are significantly larger than native frogs.
- 13-17cm from the tip of the nose to the tip of their back end (urostyle)
- Bright to dark green with white opaque skin on their bellies.
- Males have bright yellow throats used to attract females
- Females maintain a white throat that can often be lightly speckled dark green
- Bullfrogs have a large tympanum (ear) located behind their eye with a ridge of skin that wraps around the tympanum.
- Bullfrogs do not have a dorsal-lateral fold that most native frogs have (a ridge of skin that extends from the back of the tympanum towards the urostyle). However, green frogs, which are also invasive, do have a dorsal lateral fold.
- During breeding, males sound like a foghorn that repeats 2 to 3 times
Habitat and Origin
Origin: The American Bullfrog is native to Eastern North America and was introduced to Western North America, including British Columbia, throughout the 1930s to 1950s in attempts to start bullfrog farms for the sale of frogs legs locally and internationally. Throughout the 1960s to 1990s additional frogs were introduced through the pet trade when they were used as ‘living ornaments’ in backyard ponds.
Habitat: Bullfrogs prefer lightly vegetated small lakes and large ponds that stay permanently filled with water and have gently sloped banks. In BC, most bullfrog populations persist in highly modified lakes, ponds, and wetlands that few native species choose to live in.
Each female can lay from 5 to 20 thousand eggs. The eggs hatch within two to three weeks, and the tadpoles take 1-2 years to metamorphose into juveniles.
Propagation and Vectors of Spread
In BC, bullfrogs are mostly spread with the aid of humans; particularly when people collect the tadpoles as live bait for fishing but then realize they are too big for, or not palatable to fish, or when juveniles and adults are captured as pets and then released in new areas.
Bullfrogs are known as gape-limited predators, which means they will eat anything that fits into their mouths, including native amphibians, reptiles (garter snakes and alligator lizards), birds, fish, and insects, as well as their own offspring. Scientists are most concerned with their predation on native amphibians and birds and their potential to cause population declines.
What Can I Do?
American Bullfrogs have been spotted as close as West Vancouver, but their presence has not been confirmed in the Sea to Sky Region, so PREVENTION is key:
- Do not capture bullfrogs (or any frogs) and release them in areas where they do not occur, like the Sea to Sky (see attached map for where they do occur).
- When you’re out on hikes in the Sea to Sky during the day or dusk in the summer, watch and listen for bullfrogs. They often escape before you can see them, but when they jump into the water they make a short alarm call (‘eeep’) and then a splash into the water.
- The major threat to native amphibians is the loss of natural habitat, and bullfrogs live best in degraded and modified lakes, ponds, and wetlands in BC, so help conserve natural wetlands and work with local wetland and conservation societies to build new wetlands for native amphibians!
- BC Ministry of Environment, Bullfrog Factsheet, https://www2.gov.bc.ca/assets/gov/environment/plants-animals-and-ecosystems/invasive-species/alerts/american_bullfrog_alert.pdf
- Central Kootenay Invasive Species Society, American Bullfrog, https://ckiss.ca/species/american-bullfrog/
- Central Kootenay Invasive Species Society, American Bullfrog Surveillance and Eradication Program, http://a100.gov.bc.ca/appsdata/acat/documents/r52849/COL_F17_W_1222_1507657171664_7649412937.pdf
- Rylee Murray, American Bullfrog specialist, Thompson Rivers University, https://palenlab.wordpress.com/rylee-murray/