HOW LONG DOES IT TAKE FOR A TADPOLE TO BECOME A FROG ?

The simple answer

There is no simple answer to this question. Life cycles vary greatly between species and, of course, the development of the tadpoles is one major difference.

Tadpole life is often dictated by environmental factors. That is, conditions and evolutionary pressures have adapted the frogs' life-cycles to best suit their surroundings. For example, species which live in arid environments must have a very fast tadpole development in order for eggs to be laid in pools following rain and tadpoles fully develop before those pools dry up again in a matter of days, while frogs which live by permanent water sources can have a much longer development.

Another evolutionary modification is the removal of some or all of the "free-living" tadpole stage. Direct development is where the eggs are laid out of water and the tadpoles pass their entire developmental period on land, and delayed emergence is where the eggs are laid on land and the tadpoles enter the water at a relatively advanced stage of development. About one-quarter of Australian frog species use one of these methods.

Even within a single species, the time taken for tadpoles to develop can vary. There are a number of factors that determine this. One is the temperature of the water (within a comfort range, warmer water leads to faster development). Another is the density of tadpoles - overcrowding leads to the tadpoles metamorphosing at a slower rate (and maturing at a smaller size too). A tadpole can require up to 20 Litres of water for itself before it develops at its full potential.

The final stages of metamorphosis are less variable. Within two to ten days of the appearance of front arms, the tadpole will have become a "metamorphling" and will be more recognisable as a frog.

The specific answer

Bearing in mind the factors that can influence tadpole growth, there have been numerous studies that have recorded the times taken for specific species to undergo metamorphosis. Presented below is the information for those species found in Victoria. (The TADPOLE LIFE column shows how the tadpole spends its developmental period: lentic is static water; lotic is flowing water; intra-capsular indicates direct development or delayed emergence.)

The information on this page is partly conjecture but largely taken from the book
Australian Frogs (published 1989) by Michael J Tyler