The Pool Frog - Pelophylax lessonae (formerly Rana lessonae)

Note the differences between the animals on this page and the introduced Pool Frog here.

Over the years there has been considerable debate over the native status of this animal (complicated by the introduction of the remainder of the Green Frog complex). On the balance of probability it seems likely that this was, in fact a British species. The Pool Frog was formerly recorded from two sites in East Anglia although it was lost from one of these in the middle of the 19th century. It was presumed extinct in the wild at the last remaining site by 1995. A single individual known from this population survived in captivity until 1999. Other populations have become established in the UK and it is known that some of these included individuals of British origin in their founding stock.

Pool Frogs are extremely variable in colour although the North-Western types from Sweden, Norway and the UK are predominantly brown with dark brown or black irregular blotches over their backs and a lighter, often yellow, dorsal stripe. Although there is some green colouration this is generally restricted to the head area in a few individuals. Pool Frogs from most of the rest of their range are predominantly green although the markings are similar.

Adults can grow up to 9 cms. in length but males are significantly smaller. During the breeding season the males have a loud call generated by paired inflatable pouches (vocal sacs) each side of the mouth, a feature which is absent from the Common Frog (Rana temporaria). Of the three 'species' within the Green Frog complex these have the shortest back legs and the largest metatarsal tubercle (a hardened pad on the heel of the hind foot).

Unusually for frogs, the members of the Green Frog complex will bask in the sunshine on even the hottest of days. This is usually at the edge of pools and they are often detected by a fleeting glimpse as they dive into the water to take refuge.

The breeding cycle with Pool Frogs starts much later in the year than the Common Frog. It is highly dependent on the weather but coincides with the onset of warm nights in May to June. The spawn can also be distinguished. The spawn 'rafts' are typically much smaller than the Common Frog's and individual eggs are brown above and yellowish below.

The tadpoles can grow extremely large (up to 40 mms). Due to the late spawning season, unless we have a long hot summer, in which case they will metamorphose around September, they will over-winter as tadpoles and metamorphose the following Spring.

This species is listed on Annex IV of the European ‘Habitats Directive’ and with effect from 1st October 2008 received full protection under British law,   This means that it is an offence to:

• kill, injure or capture them;

• disturb them in any way

• damage or destroy their habitat

• possess them or sell or trade them in any way.

RE-INTRODUCTION

Around 50 adult and juvenile Pool Frogs and a 100 tadpoles were collected from Sweden, and after health screening were released at a site in Norfolk on 12th August 2005. Research confirmed that  a distinctly 'northern' type of the Pool Frog, was found in Sweden and Norway and formerly in Britain. The rarity of this form of Pool Frog in Europe adds a further justification for the restoration of the species to its former English range. This represented the completion of the first phase of the restoration of this species to Britain as part of the Species Action Plan for the Pool Frog.

Further releases have taken place since then and initial indications are that these were successful and the animals are now breeding.