The Green frogs, or Water frogs, belong to a genus of frogs known as Pelophylax. There are about 25 species of them distributed across the European mainland, Asia and North Africa. One species is native to the UK, although it is only found in a very restricted area in Norfolk and all the Green frogs found in the UK outside this area, including in Somerset, are introduced aliens. Identifying individual species of green frogs is notoriously difficult as they often occur in mixed populations and many of the species can hybridise with one another, a problem exacerbated by the frequency with which they are removed from their habitat, either deliberately or accidentally, and introduced to places where they wouldn’t normally exist!
In Somerset there is a large population of Green frogs occupying the peat moors north of Glastonbury and Street, centred upon the Shapwick and Ham Wall reserves. They are easily differentiated from the native Common frog, being generally larger (up to 13cm), while the ground colour is, as the name suggests, usually some shade of green as opposed to the browns of the Common frog. Often a yellow or green vertebral stripe is present, and they lack the black patch covering the ear drum, characteristically seen in Common frogs.
These are particularly noisy frogs, regularly heard chorusing during the breeding season and to the trained ear the calls can be diagnostic of the species, however regular hybridisation can blur the distinction, reducing the reliability of this as an identification technique.
During 2013 RAGS members took a number of buccal swabs from Green frogs in the Shapwick and Ham Wall reserves, and initial DNA analysis from these swabs suggest that the frogs in this area belong to the species Pelophylaxperezi, the Southern or Iberian Marsh Frog.
A further population of Green frogs has recently been discovered in the old Somersetshire coal canal at Paulton and it is hoped that these too can be identified from DNA analysis.