American Bullfrog

American Bullfrog (Lithobates catesbianus)

Report

Photo credit: ruthie62

Management Category

ID Characteristics

Description:

This species is the largest frog in North America.

Egg Masses: Jelly-like clusters of up to 20,000 eggs found on pond surfaces.
Tadpoles: Up to 15cm long, dark green to black. Tadpoles have an arrowhead-shaped body.
Adults: up to 20cm long (not including the legs) with a green to brown body and a creamy white belly. They have a distinct tympanum (eardrum) located behind the eye. Bullfrogs have a fold of skin that starts at the eye, and curves along the tympanum, ending at the shoulder of the frog. Males are generally smaller than females, and males’ tympanum is larger than their eyes, while females’ tympanum is about the same size as the eye.
Call: Bullfrogs have a distinct call that sounds like a foghorn or a bull.

Diet: American bullfrogs eat almost anything that can fit into their mouths, including other frogs, salamanders, young turtles, rodents, insects, garter snakes and even small birds.

Maturity: Eggs typically hatch in less than a week, while the tadpole stage can take 1 – 3 years, depending on location and conditions. After metamorphosis, it can take 2 – 4 years for American bullfrogs to reach maturity, and individuals can live up to 10 years.

Activity: Bullfrogs are active from April/May until September/October, depending on location. They do not exhibit sleep-like behaviour and are active day and night. During the winter, bullfrogs hibernate underwater.

Similar Species

Native

Western Toads (Anaxyrus boreas) are smaller than the American Bullfrog up to 16 cm long, and have bumpy, warty skin.

Western Toad (Anaxyrus boreas) Kevin D. Arvin, Bugwood.org

Invasive

Green frogs (Rana clamitans) are up to 10 cm long and have a ridge from their eyes to their backs.

Green Frog (J. Swiatek)

Habitat and Origin

Origin: The American bullfrog is native to eastern North America, including central to eastern portions of the US, as well as southern Ontario, southern Quebec, New Brunswick, and Nova Scotia. It was introduced to the West Coast in the 1940s for frog leg farming, and the species has since escaped or been released into natural areas in BC. This species was also imported by aquatic garden supply companies for stocking backyard ponds. Currently, this species is established in the lower Mainland and Vancouver Island. They have also been found in the Kootenays and the Gulf Islands.

Habitat: American bullfrogs require permanent waterbodies to complete their lifecycle. They can be found in wetlands, ponds, lakes, creeks, and rivers. They thrive in human-disturbed habitats.

Reproduction

American bullfrogs breed from mid-June to late July. Males produce distinct calls at night to attract females. The male’s call resembles the sound of a bull, hence the name “bullfrog”. Females can lay between 5,000 and 20,000 eggs per year.

How it Spreads

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. They can also spread on their own. This species can move over a kilometre on land in wet conditions, and if waterbodies are available along the way, they can travel up to over 5 km and establish themselves in a new location.

Impacts

Ecological:

Outcompetes native frogs for habitat and food.
As their diet includes other frogs, it can lead to the population decline of native frogs. Species at risk include the Northern Red-legged Frog and the endangered Oregon Spotted Frog.
Spread deadly viruses and fungi to other amphibians
Damage wetland habitats.

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.

Prevent the Spread

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 possess, breed, ship or release American bullfrogs in BC.
Do not collect or transfer tadpoles of any kind.
Do not stock ponds with purchased aquarium frog species.
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!

Control

Mechanical Control:

Egg masses can be removed with a fine net or bilge pump. Monitor the area every 2-3 days and remove as much of the egg masses as possible. Note that bullfrogs breed in June and July so do NOT remove eggs in the spring!

Adult bullfrogs can be captured during the breeding season when they are calling at the surface of the water. Shine a bright flashlight onto the water to find the bullfrogs. Keep the light beam on the frogs to stun them. Once stunned, approach the frog and capture it by hand or net.