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There are several non-native species of frogs and toads which
you may come across in the wild. They do not usually breed and
so far the impact on our native species is unclear.
 The
North American bullfrog Lithobates catesbeianus is a
non-native species that has successfully bred in the wild in the
UK. This animal is a significant threat to native amphibians and
sightings should be reported immediately. These frogs are huge
compared with our native frogs and will eat amphibians and other
animals of similar size. Bullfrogs have a large eardrum, at
least as big as the eye, and a fold of skin that runs over the
top of the eardrum and down towards the flank. There are no
ridges along the back. They have a very large single vocal sac
under the chin. Bullfrog tadpoles are very large (up to 15cm).
They were originally introduced to Britain through the pet trade
and probably found their way into the countryside when owners
decided to get rid of spawn or tadpoles in nearby ponds. In 1999
they bred for the first time at a site in England and have since
been controlled by Natural England.
These are
non-native frogs which often breed (and call) during the summer
months. The term 'green frog' encompasses a complex of similar
species including the
Pelophylax ridibundus,
P. esculentus and
P. lessonae. The
pool frog is a native species which
became extinct in UK and has since been reintroduced to East
Anglia. Green frogs are variable in colour but often have a
yellow stripe down the back; they usually lack the 'mask' behind
the eye that the
common frog has. The nose is relatively pointed
and the eyes are closer together than the common frog. Unlike
America bullfrogs, another non-native species, green frogs have a pair
of conspicuous dorsolateral ridges running the length of the
body. When calling, green frogs inflate a pair of vocal sacs,
rather like a pair of balloons, one either side of the head; all
have a loud call which is often likened to ducks quacking. Marsh frogs can be up to 15cm long but other
species smaller.
The African clawed toad (sometimes called African clawed frog)
Xenopus laevis was traditionally used in medical
testing (particularly in pregnancy tests) and many were released from laboratories and
hospitals as well as, subsequently, through the pet trade. It is thought to be one of the species responsible
for bringing various amphibian diseases into the UK. They feed underwater
and predate on tadpoles of our native amphibians and aquatic
invertebrates. They have a
flattened green body, large back legs and black claws on the
outer three toes of the hind feet.
Fire-bellied toads (Bombina species), including the
European yellow-bellied and fire-bellied toads and the Oriental
fire-bellied toad are sold in pet shops and have been released
at several sites in Britain. They're small, usually less than
5cm (nose to tail), and have bright yellow and black or orange
and black bellies. Oriental
species have bold green and black markings on the back and can
have orange or red and black bellies.
The midwife toad Alytes obstetricans is known to be
established in the Bedfordshire area. They're usually identified
by their distinctive call which is a clear, high-pitched
staccato whistle, often described as an 'electronic bleeping'
sound (much like a smoke alarm running on a low battery!). The
tadpoles are relatively large (up to 6 or 7cm long) compared to
the adults, which are small (up to 5cm long) and grey. Adult
male midwife toads can be seen carrying eggs
wrapped around their back legs, which is where the name comes
from.
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