Amphibians
Marsh Frog
Pelophylax ridibundus · also called laughing frog, lake frog
On a warm June evening in the marshes of Kent, the loudest thing in the landscape is a chorus that sounds like a crowd of people laughing. It comes from the marsh frog, the biggest frog in Europe, and in Britain it is not even supposed to be there.
Overview
Pelophylax ridibundus is native from western Europe across to central Asia, in the still and slow fresh water of marshes, lakes, canals, and ditches. Females reach 12 to 17 cm, making it the largest frog native to Europe. It is a highly aquatic green frog that stays in or beside permanent water all year and is a generalist predator, taking insects, fish, other frogs, and even young birds.
The laughing chorus
The male’s call is a loud, fast, cackling laugh amplified by grey vocal sacs at the corners of the mouth. It is the source of both common and scientific names — ridibundus means laughing.
The hybrid connection
The edible frog is a hybrid of the marsh frog and the pool frog, and in many populations it can only breed by mating back with a pure marsh frog or pool frog, discarding and replacing half its genome each generation.
Status
Least Concern and expanding. It was introduced to southeast England in 1935 from a Kent garden release and has spread across the region’s marshes.
Marsh Frog: common questions
Why is the marsh frog called the laughing frog?
Because of the male's breeding call. Where brown frogs such as the common frog give a soft purring croak, the marsh frog produces a loud, dry, chattering cackle, delivered in fast bursts that rise and fall in pitch and carry across open water. To many listeners it sounds unmistakably like a person laughing, sometimes like a whole crowd, especially when dozens of males call together on a warm evening. The scientific name Pelophylax ridibundus uses the Latin ridibundus, meaning laughing, for exactly this reason.
What is the difference between a marsh frog, a pool frog, and an edible frog?
They are three names in one closely tangled group, the European water frogs. The marsh frog and the pool frog are two distinct species. The edible frog is not a normal species at all but a hybrid between the two, which is why it is intermediate in size and appearance. The hybrid is fertile in an unusual way, since in many populations it can only reproduce by mating with one of the pure parent species, because it throws away half its genome when making eggs or sperm and takes a fresh copy from its mate. Telling the three apart in the field is genuinely difficult and often needs call analysis or genetics.
How did the marsh frog end up in England?
It was deliberately introduced. In 1935 a naturalist released about a dozen marsh frogs from Hungary into a garden pond on the edge of Romney Marsh in Kent. The flat, ditch-laced grazing marshes of the southeast suited the species perfectly, and with no native water frog to compete with over most of England, the marsh frog spread rapidly along the drainage network. It is now well established across Kent, Sussex, and parts of the Thames and East Anglia, and its loud chorus is a familiar sound of southeastern marshes in early summer.
Is the marsh frog a problem for native British wildlife?
It is watched but not currently treated as a serious invasive threat. Marsh frogs are large, hungry predators and will eat native amphibians, including common frog and newt tadpoles and small adults, and there is concern that in some ditch systems they suppress native species. On the other hand, England has no native water frog across most of its range, so the marsh frog is not displacing a direct competitor, and it has itself become prey for herons, grass snakes, and other predators. Its main documented effect is local rather than national.