Bullfrogs will become sexually active after 2–4 years of becoming a frog. Females are attracted to males who have territories that provide the most food. Bullfrogs mate between early spring to early summer. A male bullfrog grabs the female and begins roaring. A female bullfrog makes an aggressive call. The female lays her eggs in shallow waters. The male releases sperm on the eggs as fertilizer. A female can lay up to 20,000 eggs. The eggs of the bullfrogs are laid on the surface of water. They are then exposed to harmful UV-B radiation. Because of this, many bullfrogs may have abnormal (not normal) development. The eggs hatches after four days. They are called "tadpoles" and live in the water eating algae. Bullfrog tadpoles are larger in length than other tadpoles by other frogs. They become frogs in more than a year. In captivity, they can become frogs in twelve weeks. If a bullfrog tadpole remains as a tadpole for more than a year, it will become larger when it is an adult. Because of this, they will have a better chance at survival in the wild.