Week: 0
Life Stage: Egg & Embryo
The female frog lays her eggs usually in still, calm water. As she lays her eggs the male fertilises them and the mass of embryos are then known as "frog spawn". Each embryo is encased in a ball of jelly. Frogs tend to lay their eggs in clusters, (groups), while toads lay them in chains. Depending upon the species, the female frog can lay up to a few thousand eggs.
Week: 1
Life Stage: Tadpole (7mm)
The embryos inside the jelly turn into tadpoles, feeding on the jelly that surrounds them in order to grow and develop. One day after hatching the tadpole will start to absorb oxygen through its skin and feeds on the remainder of the jelly, (yolk) in its intestine. In two to three days after they have hatched the tadpoles open their mouths and their external gills start to work. After about 6 days the external gills start to shrivel and a fold of skin called an Operculum begins to grow over them.
Week: 2
Life Stage: Tadpole (9mm)
After 7 to 10 days the tadpoles develop the ability to swim and they start to feed on microscopic plants called algae. This is helped by the development of their eyes.
Week: 4
Life Stage: Tadpole (12mm)
Three to four weeks after hatching the external gills are completely covered by the operculum and an opening called a spiracle develops. In order for the tadpole to breath using its internal gills water is taken in through the mouth and passes over the gills before being expelled through the spiracle. The tadpoles start to grow in size quite quickly and their tail widens to help them to swim.
Week: 7
Life Stage: Tadpole (28mm)
The hind legs start to form. Buds appear first and the legs then start to develop.
Week: 9
Life Stage: Tadpole (35mm)
By week 9 the hind legs are fully developed and the head starts to broaden. The front limbs of the tadpole start to develop, initally developing inside the body and appearing as small bulges below the operculum of the tadpole. The tadpoles develop lungs for breathing out of water and lose their internal gills. They also now have a well-developed coiled gut so they can digest more complex foods. The tadpoles' diet now changes from herbivorous, (eating plants), to carnivorous, (eating animals), and they start to feed on small insects and larvae.
Week: 11
Life Stage: Tadpole (35mm)
The front limbs emerge, appearing to pop out from the spiracles, elbows first.
Week: 13
Life Stage: Tadpole (25mm)
The tail has begun to shorten, reducing the length of the tadpole. The mouth becomes broader, and the eyes become more prominent.
Week: 14
Life Stage: Tadpole (20mm)
The tail continues to shorten until it disppears completely, by which time the tadpole looks like a very small frog.
Week: 16
Life Stage: Frog (15mm)
The frog has now completely lost its tail and it leaves the water for the first time to explore the land. It will now spend most of its time on land, depending on how abundant its food supply proves to be. If there is more food in the pond then it may spend longer in the water. The young frog will remain near its birth area for sometime before exploring the wider surroundings on land. The adult frog will be ready to breed in about 2-3 years.
Stages of the Frog Life Cycle
Egg: Unfertilised gamete laid by the female frog
Embryo: Fertilised egg that has begun developing
Tadpole: Frog larva
Frog: Adult frog
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