The life cycle of a frog begins as an egg that is laid by its mother and is fertilized outside of her body by its father. This egg laying/fertilization process is called spawning and is the very beginning of a frog’s life cycle. After the frogs have spawned the male will exit, but the mother may remain to look after the eggs. This occurs in some, but not all, frog breeds. The eggs are almost always laid and fertilized in shallow, calm water in very large numbers. The large number of eggs is nature’s way of compensating for predators that eat the eggs.
Approximately 7-9 days after being fertilized, the eggs will hatch. The hatchlings emerge as tadpoles (also known as polliwogs). For the first week of tadpole life, the tadpole will eat the remaining yolk sac in its gut. After about 7 days of development, the tadpole will begin to swim around and eat algae off of the surface of the water. Initially, the tadpole consists of little more than gills, the mouth, and the tail. By the fourth week, the tadpole has begun to grow skin over its external gills. Eventually they will disappear. The tadpoles become “social” creatures, and will even school up and swim together.
Tadpoles lack true teeth, but instead have rows of small keratinized structures called keradonts. While tadpoles are usually herbivorous, some species can be carnivorous. The carnivorous species will eat things like insects, smaller tadpoles, and even small fish. After about 6 to 9 weeks, the tadpoles begin to sprout legs. Their head begins to become more distinct and their body elongates towards its more adult shape. Their arms start to bulge out, and will eventually pop out elbow first.
After 9 weeks of tadpole development, the frog has front legs and resembles a really small frog with a long tail. By this stage, the vast majority of frog breeds eat small insects. At this stage it is no longer called a tadpole, but instead is called a froglet. It is well on its way to adulthood, and will soon begin to go through the process of metamorphosis.
Between the age of 9 and 12 weeks, frogs begin to go through the process of metamorphosis. This is the transitional phase from froglet to adult frog. They begin to lose their tail and develop an adult digestive system. Their eyes grow rapidly and move further up their skull. Their jaws transform into the large jaws of a predator.
By 16 weeks, the tadpole has matured and transformed into an adult frog. It will leave the water to hop on land. It will move back and forth between water and land in true amphibian style until it at last returns to the water to mate and begin the life cycle all over again.