Already this year BRERC has received an increase in the number of records for ‘green frogs’ from our region, including records from the Cam Valley and Frenchay. There are three types of ‘green frog’ – Edible, Pool and Marsh Frog. All look very similar and are difficult to accurately distinguish with any certainty when out in the field. The Pool frog, now thought to be extinct in Britain, is currently being investigated to determine if it was ever a true native to Britain, based on archaeological and other evidence. The other two species are considered introduced although there has been some speculation as to their true statuses. None of these frogs have been considered native to our region and are classified as introduced.
The apparent sudden appearance of ‘green frogs’ in different parts of the region may be cause for concern. They have been present and are becoming more widespread in parts of the south west, particularly on the Somerset levels and moors, for some years now and we could expect them to eventually become established in parts of Avon. However the most likely areas we would have expected them to arrive in would have been the North Somerset levels and moors and not necessarily the Cam Valley or parts of Bristol. Exotic frogs do occasionally get released from captivity (which is illegal) but it seems odd that so many have appeared so suddenly.
Although they are thought to be potential predators of newts and other aquatic life it has not yet been established what impact they actually have on their new environments.
So what is a ‘green frog’? Most people might paint a picture of a frog coloured green. However our native Common Frog is usually brown, and is part of a group of frogs known as ‘brown frogs’. The ‘green frogs’ tend to be a dark green. Confusingly most frogs can have considerable variation in colour and markings so you can occasionally find green ‘brown frogs’ and brown ‘green frogs’.
Often the ‘green frogs’ will have a thin yellow stripe running down the length of its back, will appear less patterned or marked and has a more pointed head than Common Frogs. Apologies for the not very good photograph, but you should be able to see the stripe.
The most striking thing about them, particularly in late spring, is their noise. They are extremely loud, something like a cross between a generator, a duck and a warbling pig. They have throat sacs that inflate when they are calling. Sometimes you can get very close to one, without seeing it at all and yet you have this wall of sound in front of you, seeming to come from nothing.
‘Green frogs’ are more aquatic in lifestyle than our native frogs. It is possible to spot them though as they can be found basking on the waters edge or among emergent vegetation and they will call both during the day and by night. If you find a population of them you may spot many small ones along with some very large examples in the same area.
Please let us know if you see or hear one.