Life Cycle of a Frog: Tadpoles

A frog's life starts off with an egg. A female frog lays thousands of these eggs into water in a jelly-like coating. Frogs lay these eggs in clusters whereas toads lay eggs in long chains.

These eggs (frog and toad) are highly susceptible to attack from predators, so as a result of evolution frogs have developed a number of ways to protect their eggs. A common way to ensure survival is synchronised reproduction, which means frogs will breed at the same time. Although there are thousands of eggs produced from each frog the majority do not survive due to predator attack. Another more drastic measure is the effort of the cane toad. The cane toad lays poisonous eggs to try reducing predator attack. 

When the eggs hatch, life is continued on in the form of tadpoles. These have a ovular shaped head with a long flat tail. The tadpoles are very basic organisms. they have no eyelids and their skeleton is made of cartilage. They have external gills but develop internal gills later on in life. Some species of frog develop inside the egg and hatch as small frogs. Most of the time tadpoles are herbivorous and feed of algae in the water. Some species, however, are carnivorous and feed of small insects. The later the tadpoles develop legs, the more likely they are to survive, as tadpoles that develop quickly are often eaten.

Predators of the tadpole include fish, newts, beetles and birds. The tadpole stage of a frog may only last a week, but it could also last as long as a year.

At the end of the tadpole stage, the tadpole undergoes a change. The change itself only lasts about twenty four hours. During this change, the tadpole develops into adulthood. These changes include:

The legs are formed from the disappearance of the external gills. The jaws change into predator jaws from small filter feeding jaws. The digestive systems are formed. The eyes enlarge and eyelids are formed. A nervous system is formed and the eardrums develop.

The tail will still remain for a while, but once it has been absorbed by the frogs body, the frog can leave the water for the first time.