In the UK during the summer, most tadpoles will grow into frogs and leave the water for their new life on land. However, some tadpoles will over-winter and grow into frogs the following spring.
In colder climates the water can either dry up or freeze over which limits the number of tadpoles that can do this.
In the UK we tend to have milder winters and most of the time the water doesn’t freeze which makes it possible for tadpoles to over-wintering.
Why so some tadpoles over-winter?
It’s not really clear why some tadpoles over-winter but some scientists feel that temperature and the availability of food could be factors.
Some suggest that the tadpoles decision to over-winter may have been made early in the season.
The environment could also influence over-wintering, for example if the tadpoles are living in higher altitudes. Tadpoles living in places like Wales or Scotland would likely experience lower temperatures and less available food.
Tadpoles that live in places like this are better able to tolerate the colder temperatures.
Some tadpoles are even able to put up with freezing for short periods of time! Doing this increases their chances for survival.
In central Europe, over-wintering will vary by species and is more typical in later breeding species with large tadpoles for example:
Over-wintering for common frogs is rare and was reported for the first time in the Netherlands in 2013. Scientists feel that overwintering could be due to unusual weather conditions.
If there is a very cold winter, some frogs may breed later in the year. This would mean that the tadpoles get a later start with their growth and development.
Cool conditions early in the autumn could trigger slow development and a mild winter could mean over-wintering by tadpoles in certain species.
Even though still rare, over-wintering may become more common across Central Europe with changing weather conditions causing warmer temperatures.
There are 15 species of ranid frogs but only five of these species are known to over-winter as larvae:
North American bullfrog
Drought is one of the main factors that limit ranid frog species in North America from over-wintering as tadpoles.
Requirements for Development
In Northern United States, the southern leopard frog is a common frog that lives in freshwater ponds. Tadpoles of this type of frog will stay in the larval stage and if by autumn, it doesn’t reach a certain size they will likely over-winter.
If winter conditions are suitable, tadpoles could stay in the pond for several years until they reach a certain size.
Common frogs in the UK do not need to reach a certain size but they do require specific environmental conditions.
While most tadpoles will develop and leave the water before winter sets in, you may occasionally see them in the water over autumn and winter.
If you see tadpoles in the water later in the year, it’s best not to feed them or take them out of the water.
But, if the water where you find the tadpoles is overgrown then you could trim it back. Doing so will let more light and warmth into the water.
Otherwise it’s best to leave the little guys alone, hopefully they will survive the winter and will be counting the days till spring!