Did you know that one of California’s top 10 invasive species lives right outside your door?

In fact, you can hear its distinctive call in the early evenings. It sounds a bit like a humming cow which is maybe why it has “bull” in its name.

It is the American Bullfrog or Lithobates catesbeianus.

The native habitat of the American Bullfrog is eastern North America. However, the American Bullfrog is invasive in the West.

Here in California, it was introduced by the gold miners in the late 1800s and early 1900s as a food source, but it quickly spread to aquatic and semi aquatic biomes throughout California.

The bullfrog is a carnivore, or a secondary consumer. It eats mainly primary consumers like small fish, baby birds, small mammals, other amphibians, tadpoles and lots of insects; basically, whatever it can fit in its very large mouth.

It can grow up to 8 inches long and can weigh up to one pound. It has large and powerful legs and in the winter months can travel up to a mile per day looking for food.

This massive frog is a dangerous predator here in California and has been decimating our native amphibian populations since it arrived, most specifically the vulnerable red-legged frog (Rana draytonii) and the endangered foothill yellow legged frog (Rana boylii) who lives here in our local watershed.

In fact, red-legged frogs were the basis for Mark Twain’s famed short story “The Celebrated Jumping Frog of Calaveras County”, but they are now so scarce that bullfrogs are used for the competition instead.

There are three main reasons why the bullfrog is threatening our native ecosystems.

First, at several stages in its life cycle the American Bullfrog preys upon our native frogs. Although the bullfrog tadpoles are mostly herbivorous, they will occasionally eat smaller, native frog tadpoles and insect larvae.

Further, as adults the American Bullfrog both competes with and eats native amphibians in such high amounts that one study done by a UC Davis ecologist in San Joaquin County showed a survival rate of just 5% of native red legged frogs in areas with bullfrogs compared to areas without.

Second, the bullfrog reproduces at a rate 10 times higher than the native frog population and can lay 20,000 eggs per clutch and two clutches per year compared to the native frogs which average 2,000 to 3,000 eggs per year.

This high reproduction rate combined with its ability to travel and quickly invade new water systems makes the bullfrog hard to eradicate completely and a dangerous competitor.

Finally, the bullfrog carries the chytrid fungus (Batrachochytrim dendrobatidis) but is not affected by it.

The chytrid fungus is a severe skin disease that causes death in susceptible native species. It disrupts the function of the skin in both the tadpole and adult frogs and specifically affects the native Californian mountain yellow legged frog.

This fungus has caused the extinction of 100 amphibian species worldwide since 1970.

So, what can we do about this voracious, opportunistic predator?

California allows the importation of bullfrog tadpoles as pets and adults for food. Approximately 2 million are brought here annually and many of them are released or escaped to wreak havoc on native ecosystems. Banning importation or increasing permit fees can help limit the negative impacts.

Also, we as residents can help! We can report bullfrogs when we see them and not keep them as pets.

If you are on a hike or see a bullfrog in your neighborhood you can report it to the CDFW Invasive Species Program or email to This email address is being protected from spambots. You need JavaScript enabled to view it., or by calling 866-440-9530.

Callum is a 13 year old student in Davis, California.