Species Infomation
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Portrait of Green lizard
North American Bullfrog Lithobates catesbeianus

BullfrogThis is a huge frog which can grow to 15 cm long.  It is wary and can be difficult to get a good look at.  However, it calls loudly on warm nights during the summer making it easily identifiable.  It sounds reminiscent of cattle.

Due to the ecological threats posed by this species, its import into the EU has been banned.  The chances of finding bullfrogs in the UK are now slim but even so, two populations have been discovered in southern England within the last ten years.  It is very important that any other bullfrogs are reported.


Bullfrog tadpoles can spend several years in the water, hence they grow very large, relative to common frog and toad tadpoles.


Juvenile Bullfrog

Identification tips

Bullfrogs are potentially confused with marsh frogs (also large frogs which call loudly).  There are some features, however, that distinguish the two species:

(A) When calling, bullfrogs inflate a single vocal sac under the throat rather than the two sacs on either side of the head like the marsh frog.

(B) Bullfrogs do not have dorsolateral ridges which are usually prominent in marsh frogs.

(C) The calls of the two species are different; bullfrog calls are reminiscent of cattle while marsh frog calls are more likely to be mistaken for waterfowl.

Alien call signs

Bullfrog Marsh frog

To hear these you may need to click here to install the appropriate plugin.
The GB Non-Native Species Secretariat has a downloadable identification guide.