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Invasive non-native species (UK) – Marsh frog

marsh frog

In the last article of our ‘Invasive Non-Native Species’ series, Elizabeth Kimber looks at the marsh frog…

Marsh frog (Pelophylax ridibundus) originate from the eastern half of Europe into western Asia.  They were regularly imported into the UK from the late nineteenth century and were introduced to the Walland Marsh in Kent in 1935, from Hungary.

Marsh frog are now predominantly found in south-east England, with populations in Devon, Bristol, Isle of White, Norfolk and Cornwall.

marsh frog

Photo credit: GBNNSS ©RPS Group Plc

Identification & Ecology
Identification features of the marsh frog include:

  • Variable in colour and pattern – generally brown to green with dark green blotches.
  • Females can be up to 13cm in length, males are normally smaller.
  • Pronounced snout with a wide gape.
  • Eyes are close together.
  • There are two parallel skin folds on back.
  • The male has two dark grey vocal sacks, one on each side of the mouth.
  • The skin is granular.
  • Calls with loud, quacking or laughing sound in early summer.

Habitat suitable for marsh frog includes similar habitats to our native amphibians, favouring ponds and streams along with marshland dykes and fisheries. There has been evidence to suggest that the marsh frog can utilise rivers to increase their range. The marsh frog is active both during the day and at night, basking in sunshine during the day.

The main impact from marsh frogs is likely to be on our native species, both by predation and by carrying diseases to our native amphibians.  Hybridises with closely-related species and thus could affect native (re-introduced) pool frogs if the range extended.   Marsh frogs can be a significant prey item for grass snakes in some areas.

The marsh frog is known to be a vector of chytridiomycosis which can be a threat to native amphibians. Infections of chytridiomycosis in native amphibians affect individuals by attacking their skeleton and skin. The chytrid fungus is waterborne so can accidentally be spread between waterbodies. This makes it critical to disinfect all footwear and equipment before moving to other waterbodies to avoid spreading the disease.

marsh frog

Photo credit: GBNNSS ©RPS Group Plc

Legislation which attempts to control the distribution on marsh frog includes Schedule 9 of the Wildlife and Countryside Act, which makes it illegal to distribute or allow the release of marsh frog into the wild.

Control Measures
Currently there is no requirement to manage the population of marsh frog in the UK, as this would be challenging to achieve and would require identification of each individual to ensure no harm to any native species.


  • Non-Native Species Secretariat (NNSS) HERE
  • Meet the Species HERE.
  • Kent Reptile & Amphibian Group (KRAG) HERE.

Header Image: Photo credit: GBNNSS ©RPS Group Plc

About the Author: Elizabeth Kimber works for an ecological consultancy based in Dorset (Lindsay Carrington Ecological Services Ltd). As part of the role she manages the ecological works for a multi-phase development. She conducts protected species surveys and holds a class 1 bat licence, smooth snake and sand lizard licence. She can be contacted via email: liz (at)