While conducting a trash assessment in a Contra Costa Creek last week, out of the corner of our eyes we noticed what looked like a fish poking its head out the water, taking a gulp of air. Upon closer inspection, it turned out not to be a fish, but instead a huge tadpole, dotted with black spots and around 5 inches in length: an American bullfrog tadpole.
American bullfrogs, Lithobates catesbeianus or Rana catesbeiana, are native to southern and eastern United States, but has been introduced across the country and into western states, including California where it is considered an invasive species. Common in California, some contribute the rising bullfrog population as a factor in upsetting the ecological balance of native species, including the vulnerable California red-legged frog. The bullfrog has a voracious appetite and they will prey on anything they can find and overpower, including rodents, reptiles, birds, amphibians, fish and insects. With this opportunistic appetite, bullfrogs can dominate the food chain, squeezing out other species of native frogs.
Known for their size, these bullfrogs are the largest frogs found in North America and when fully grown, can reach up to 8 or more inches long and weigh up to 1.5 pounds. Females are larger than the males, while male bullfrogs distinguish themselves with a yellow throat. Both male and female frogs are olive green with some dark markings and a white belly. The bullfrogs are incredible jumpers, and can jump over 10 times their body length in one motion. While we found the tadpole in a creek, bullfrogs usually inhabitat lakes, swamps or marshes. The bullfrog gets its name from its distinctive call that resembles the mooing of a cow that can be heard up to a half mile away. During mating season, usually in the late spring and early summer, males join together in a “chorus”, all calling together and attempting to capture the attention of a discerning female bullfrog.
Bullfrogs are sources of food of many other species, including people. Large birds that live by the water, such as herons, prey upon the bullfrog as do river otters and alligators. People catch the bullfrogs for food for the back legs. The rest of the body is usually not consumed. While some have attempted to breed bullfrogs for food, so far this has not been successful.
Keep your eyes open for these large creatures as you explore the Bay. They have been found all over the East Bay, including tadpoles in Lake Anza!