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There could be a number of reasons why you might notice tadpoles
disappearing:
Sometimes tadpoles may not have disappeared at all, they are
simply hiding in the silt at the bottom of the pond or in the
vegetation around the edge. As they grow larger they tend to
become more secretive and the fewer tadpoles you have, the
harder they are to spot.
Tadpole development can often be dramatically fast in favourably
warm periods, so in many cases ‘disappearing’ tadpoles can
suggest that metamorphosis has taken place and froglets have
emerged en masse and into the surrounding habitat
without you ever being aware. Tadpoles usually spend between 15
and 25 weeks in the water.
This is a very risky time for amphibians, since tadpoles are
eaten by almost every aquatic predator there is - in and out of
the pond. The list includes dragonfly larvae, diving beetles,
water boatmen, newts, ducks, blackbirds and grass snakes. Again,
this is nothing to worry about since in most cases some of the
tadpoles will make it to emerge as froglets (the fewer there are
the harder they are to catch and for you to see). If there is an
unusually large predator population this could have a big impact
on the tadpoles; often these things balance out eventually.
Tadpoles feed primarily on the algae that grows on plants and
rocks in the pond, along with decaying matter such as dead pond
animals and tiny invertebrates. In some ponds that are newly
created or poor in nutrients there may be little food available.
This can lead to a limited population size, slower growth and
later emergence, or even cause the tadpoles to over-winter in
the pond. Longer development times are not normally something to
worry about, and adding food is not recommended as it can lead
to excess nutrient levels. Over-wintering of tadpoles can also
occur if there is a mild summer or if your pond is in a shaded
position that means less light is reaching the pond. The algae
that the tadpoles feed on requires light to grow so in some
cases it might be worth cutting back overshadowing branches or
foliage near your pond. In rare instances you may also come
across neotenous tadpoles. These are tadpoles that are unable to
metamorphose and hence continue growing, occasionally to lengths
of up to four inches! Please let us know if you notice tadpoles
of this size in your pond since it is possible you might
unknowingly have an exotic species of larger amphibian that has
taken residence in your pond.
FAQ:
Tadpoles are being
preyed upon, what can be done?
Contact us.
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