Q: How does a bullfrog tadpole grow into a frog?
Dan – Clovis, CA
A: What would a pond or lake be without bullfrogs? These croaking amphibians – which can grow to 8 inches in length and weigh up to 1½ pounds – reside near water sources, like lakes, ponds, rivers and bogs. The brown-green frogs with the scientific name Lithobates catesbeianus prefer warm, still, shallow water.
Through their seven- to nine-year life cycle, bullfrogs pass through several stages of development. Ever wonder what happens during those stages? Keep reading, because here’s what you need to know.
From Eggs to Tadpoles
Bullfrog breeding, which happens externally, takes place in May to July in the north and from February to October in the south. The female adult bullfrog, which sports a white throat during the mating season, deposits as many as 20,000 eggs in a foamy film in quiet, protected waters; the male, which has a yellow throat during mating rituals, then fertilizes them. Four days later, tiny tadpoles emerge. The little guys are able to fend for themselves right away and will stay in their tadpole stage for almost three years before transforming into adults.
While they’re in their tadpole – or pollywog – stage, the tiny gilled critters live exclusively in the water and nibble on water plants for nourishment. At first, their bodies, which can measure up to 6¾ inches long, are long and narrow and include a tail where they store fat when food is in short supply during the winter months. After about one year, the tadpoles will start to grow legs. Shortly thereafter, they grow arms. And then, their tails shorten, they develop lungs, and their gills disappear. The tadpoles have transformed into froglets.
From Aquatic to Terrestrial
After that two- to three-year tadpole-to-frog developmental period, the bullfrog ’s final growth stage is when the froglet hops from the water to dry land. Thanks to its fully developed lungs, the now-carnivorous and aggressive frog can now breathe oxygen, and that gives it the freedom to emerge from its watery first home to the shore where it can hunt for anything that will fit in its mouth, including insects, small mammals, birds, fish and other frogs. The adult bullfrog rests by day, and defends and hunts its 3 to 25 meters of shoreline territory by night.
Finally, after three to five long years of growth and development, the tadpole has become an adult bullfrog and reached sexual maturity – and the life cycle begins again. Bullfrogs in the wild live to about 7 to 9 years old; in captivity, they can live as long as 13 years.
Now the next time you hear your bullfrogs croaking, you’ll have a new appreciation for them!
Pond Talk: What’s your favorite part of having bullfrogs in your lake or pond?