Frogs and Tadpoles
by John Walsby
If you asked a class
of primer children what animals lived in ponds and streams, the
first to come to their minds would probably be frogs and tadpoles.
Most would be less aware of the other creatures described in the
other articles in this series. Many of you have probably collected
tadpoles and kept them in a bowl when you were younger. You were
lucky to be able to do so in New Zealand for, if two closely related
species had not been introduced from Australia in the middle of
the last century we would not have tadpoles in our streams and
ponds in the summer.
We do have native frogs
in New Zealand, but all three species are very rare and none of
them have free-swimming tadpoles. Instead of laying long strings
of eggs in a spawn mass in water, our native frogs lay just a
few large eggs in damp places beneath stones and logs. The tadpole
stage is completed within the eggs and when they hatch it is small
froglets that emerge.
You are unlikely to
see any of our native frogs unless you make special expeditions
to find them. The frogs that you do see around ponds, lakes and
swampy land are either the golden bell frog, Litoria raniformis,
found throughout New Zealand, or the green frog, Litoria aurea
which is confined to the northern half of the North Island.
Both of these frogs
are handsome animals growing to 75 - 90 mm at full size and coloured
green with golden-brown blotched markings. Those seen hopping
along roads at night in the spring are probably on their way to
favoured breeding ponds to mate and lay spawn.
The young tadpoles
feed on algal films but about the time they start to grow leg
buds they start taking small animals in the water. As the hindlegs,
then forelegs develop, the fishlike tail is steadily resorbed
as the change from tadpole to froglet occurs. Froglets leave the
water but stay close by so they can always return to keep their
skins moist.
