Eggs to tadpoles
After mating, female frogs and toads lay eggs. Inside the eggs, small tadpoles begin to form. These immature frogs start life by eating their eggs. Then they hatch out and eat green plants like algae.
Tadpoles to frogs
Tadpoles have small mouths adapted to eat plants. They have long intestines (like most herbivores) that help them to digest plant material. As they eat and grow, they begin to transform into an adult. While some tadpoles transform (through metamorphosis) into frogs in a few weeks; other take several years. If you find a large tadpole in the spring, it is most likely a green frog or bullfrog tadpole that hatched last spring and survived the winter as a tadpole.
As they change from tadpoles to frogs, we can see the changes to the outside of their bodies. First they grow back legs, then front legs. Their tail slowly disappears as it is absorbed into their bodies. But there are a lot of other changes happening inside! Their intestines are becoming smaller. As adults they will be carnivores, and carnivores don't need long intestines. Their mouths are becoming much larger, and they are developing a long, sticky tongue. And the gills that have provided them with oxygen in the water are being replaced by lungs that will let them breathe oxygen from the air. When you stop to think about it, it is really quite amazing!
Learn how to identify Wisconsin's frogs and toads or Join the Frog Chorus.
Watch this video. It has some great footage of tadpoles transforming into frogs. The video mentions how long each phase of the tadpole's life will take. Remember that the timing depends on the species of frog and the temperature of the water.
