Tadpole to frog: development stages and metamorphosis

I can still remember watching in fascination as tadpoles, which were held in a tank in my classroom, developed legs and began to climb out of the water. Many years later, and a few years wiser, I am still just as amazed by this process as I ever was.

If you have a wildlife-friendly garden pond one of the biggest miracles of nature is likely to be happening in it in early spring. The frogs lay their eggs in February. Each female will have laid somewhere in the region of 2,000 eggs in a ball of jelly. Many eggs die, turning opaque when they do, but the rest will take about two weeks to hatch.

When tadpoles are first born they are little more than a mouth, gills and a tail. Inside their gut is the remainder of the jelly from their egg and this sustains them for the first few days of life. After about a week the tadpole will be strong enough to swim and search for food, which for the next few days of life, consists entirely of algae.

After about four weeks the tadpole starts to lose its gills and develop teeth. Soon after this their back legs develop, their diet changes and they become carnivorous. They will eat any animal matter they can find whether dead or alive. Try putting a finger in the pond and they might even help you to exfoliate. After another few weeks the tadpole develops front legs and the head shape of a frog.

The final change occurs as the tail becomes reabsorbed by the tadpole and utilised as a source of protein. This is when the tadpole ceases to be a tadpole and becomes a tiny frog, often referred to as a froglet. It emerges from the water becomes completely carnivorous and breathes both through its moist skin and by using its lungs.

The whole process of metamorphosis will have taken about three or four months and these froglets will remain on dry land for the next three years before they are sexually mature and will return to water to breed for themselves.

As I sit and watch them I often wonder how many of the two thousand eggs will make it that far?

David Chapman's stunning photograph of the tadpole won first place in the 'Wildlife in the Garden' section of the International Garden Photographer of the Year competition. About taking the photograph he says:

A tadpole of a common frog, Rana tamporaria, resting on an aquatic plant under water. I was photographing the life-cycle of the common frog and I think this was the most photogenic stage in its development. I loved the way the tadpole pushed up the meniscus of the water surface from underneath. I used a vivarium and rested the stem of an aquatic plant inside. I introduced the tadpole and waited for it to climb the stem and touch the underside of the meniscus.

Development stages of a tadpole to a frog: a timeline

• Frogspawn, week 1: laid in February, two to three weeks hatching time.
• Hatchling tadpole, week 3: the first week after hatching the tadpole might not be visible as it doesn't have the energy to swim. It'll camouflage itself while it eats the jelly in its stomach.
• Swimming tadpole, week 4: after a week the tadpoles will have strength to swim and will be looking for food. They'll only be eating algae.
• Toothed tadpole, week 6: at about four weeks old tadpoles grow teeth and more complex digestive system develops. Their diet expands to include small insects.
• Tadpole with legs and tail, week 7: at about five weeks old the tadpole will gradually start to grow legs, starting with the back legs.
• Froglet, week 14: 12 weeks after hatching the tadpole now looks like a tiny frog with a tadpole's tail. The lungs should have also developed by this point and the froglet can start venturing out of water.
• Young adult frog, 16: at around 14 weeks old the tadpole's tail drops off. The metamorphosis is complete and the tadpole has become a young frog.

Tadpole development: how long does it take?

The development time between frogspawn being laid and young frogs leaving the pond is about 16 weeks, give or take. The time it takes for a newly hatched tadpole to become a frog is around 14 weeks.

What do tadpoles eat?

What tadpoles eat depends on their stage of development. They start by eating the jelly from the frogspawn, then move onto algae after a week. Once their teeth grow at about four weeks old they become carnivorous and eat small insects.

What to feed tadpoles

If you'd like to feed the tadpoles in your pond you can feed small amounts baby spinach or other leafy vegetables to them while they are young, but remove any uneaten food before it spoils. Goldfish flakes and insect larvae are also suitable. However by keeping your pond wildlife-friendly and biodiverse your tadpoles should not need to be fed.

Interested in having your own garden pond to attract tadpoles and other sorts of wildlife? Read our guide on how to build your own wildlife pond, then be sure it’s kept in the best condition with our top tips to pond care.

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