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Bombina bombina, the European fire-bellied toad, is a small, warty amphibian of the family Bombinatoridae. Its range runs through Central and Eastern Europe, from eastern Germany (with pockets in eastern Denmark and southern Sweden) east to Russia’s Volga District, where the Ural Mountains stop it, and south to Bulgaria and the Marmara region of Turkey. An introduced population also lives in Lorraine, France, more than 500 km from the natural range.
Identification
This is a medium-sized frog, growing to about 56 mm. The back is warty, in shades of grey, brown or green, giving it good cover against muddy pond bottoms and submerged vegetation. The belly tells a different story: it is red with thick black mottling, normally hidden but flashed when the animal feels threatened. Confronted by a predator, it arches its back, lifts its limbs and sometimes flips fully onto its back to display that red underside, a defence called the Unkenreflex — a textbook case of aposematism, warning colour backed by the mildly toxic bombinins its skin glands produce.
Habitat and range
Within its Central and Eastern European range, Bombina bombina keeps to lowland ponds and marshes with little woody vegetation. In larger lakes it does not use the open water, staying instead in the shallow edges, 50 to 70 cm deep, among reed beds and floodplains. That preference for seasonal, sun-warmed lowland water separates it from its closest relative, the yellow-bellied toad (Bombina variegata), discussed below.
Behaviour and breeding
Bombina bombina feeds on small invertebrates such as springtails, beetles, flies and ants. Below about 4°C it burrows into soil or under logs and goes into torpor for the winter, emerging once the water warms; breeding activity starts once the water reaches around 16°C, mostly at night or in the early morning. Males call with a distinctive “whoop,” carried further than related species’ calls thanks to internal vocal sacs.
A female lays her eggs in small batches, 15 to 40 at a time depending on her body size, attached to submerged plants. The eggs hatch after about a week, and the tadpoles complete metamorphosis after roughly a month, by which point they measure about 3.8 cm. Tadpoles face leeches and fish as predators, while adults are taken by snakes and birds.
Conservation
The IUCN category is in the facts box above. Even so, local declines are documented: in Denmark, 15 breeding populations were recorded in 1974, but only 8 remained by 1988. Targeted habitat work can reverse that trend — in Denmark’s Funen County, digging dozens of new ponds roughly quintupled the local population within a decade. Researchers have also studied the species’ bombinins, antibacterial and antifungal compounds from its skin, for potential use in food packaging to slow spoilage.
Similar species
The species most easily confused with Bombina bombina is its close relative Bombina variegata, the yellow-bellied toad, which arose from it through clinal speciation during the Pleistocene. Where the two ranges meet, they form hybrid zones about 2 to 7 km wide. Habitat is the more reliable field clue: Bombina bombina is more aquatic and sticks to seasonal lowland ponds, wet meadows and floodplains, while Bombina variegata is more terrestrial, with longer legs and thicker skin, and favours higher-elevation, short-lived pools. The introduced French population is a particular concern on this front, since it could hybridise with and affect local yellow-bellied toads if the two come into contact.