Photo · Romain Savary
Everything about the largest rodent in Europe — its history, biology, role in our rivers, and its slow recolonization of French-speaking Switzerland.
Known as Castoroides ohioensis, the giant beaver was the largest rodent in North America during the Pleistocene1, and the largest beaver that ever lived. It haunted the continent's wetlands for nearly two million years, on a branch close to that of our own beavers, before dying out without descendants.
Its size is impressive: up to two meters long, tail included, for around a hundred kilos — the build of a large wild boar. For a long time it was described as "as big as a black bear," and much higher weights were put forward; since mass has been estimated from the femur rather than the skull, the figures have narrowed: 60 to 100 kg in the reference study, up to 125 kg according to older authors. Its extinction is thought to date to nearly 10'000 years ago, at the end of the last glaciation, at the same time as the mammoth and most of North America's large mammals.
Yet it is not their ancestor. Castorids are divided into several subfamilies: the giant beaver belongs to the Castoroidinae, today's beavers to the Castorinae. These are two sister branches, born of the same semi-aquatic beaver of the early Miocene, some twenty million years ago. Each then went its own way: the giant's line ends in the Pleistocene without leaving descendants, while the other still carries the two species alive today.
Much earlier, the ancestors of the American beaver left Eurasia by crossing Beringia — not a narrow isthmus, but a vast exposed plain that connected Siberia to Alaska whenever sea levels dropped. The North American beaver then diverged from the Eurasian beaver: mitochondrial genomes place this split at around 7.5 to 8 million years ago, and the oldest North American beaver fossils are indeed that age.
Originally, the beaver's range extended across large parts of Eurasia and North America. Today there are two species: Castor fiber (Eurasian beaver) and Castor canadensis (American beaver). No mating between the two species has ever produced living offspring: their karyotypes do not match — 48 chromosomes in the Eurasian beaver, 40 in the American — and captive crossbreeding attempts have all failed, even though matings have indeed been observed. The American beaver also lives in the wild in Europe: seven individuals were released in Finland in 1937, at a time when only a single beaver species was recognized, and their descendants now occupy Finland and north-western Russia. In Old French, the beaver was called bièvre, from the late Latin beber, itself taken from a reconstructed Celtic form, *bebros: the same Indo-European root as the German Biber or the English beaver, meaning "brown." The learned word castor, from Latin, eventually won out, but the name has survived on our maps: Bever and its stream the Beverin in the Engadine, Biberist (SO), Biberstein (AG), Bibern (SH), or the Biber that gives its name to Biberbrugg (SZ). French-speaking Switzerland, for its part, has kept almost none.
The Castor fiber is only one of the many species produced by the long diversification of castorids, which first appeared at the end of the Eocene, some 37 million years ago. It colonized nearly all of Eurasia. On the other side of the Bering passage, the North American populations followed their own path; the sea covered this passage for the last time around 11'000 years ago, closing the door between the two worlds for good.
The giant beaver's skull is four times larger than that of today's Eurasian beaver. Its incisors are long, ridged and curved, while those of the Eurasian beaver are shorter and orange.
Logarithmic scale — each gridline represents ×10 · Ma = million years
First appearing at the end of the Eocene, castorids diversified across Eurasia and North America. Early in the epoch, two sister branches diverged: that of the genus Castor and that of the giant beavers. Around 8 million years ago, the European and American lineages of the genus Castor split in turn.
A short, pivotal epoch. The Bering Strait has just opened, the climate is cooling, and Castor californicus already inhabits western North America.
The Quaternary glaciations and their megafauna — the mammoth. Castoroides ohioensis reigns here: up to 2 m and around a hundred kilos. It dies out around 10'000 years ago, and its branch with it.
Giant beaver †Castor fiber is the only beaver native to Europe. Hunted to disappearance in Switzerland, it was reintroduced there from 1956.
The giant beaver did not leave only bones behind. Several North American nations tell of a great landscape-building beaver, whose dams and their breaches explain the shape of the land: the Outaouais rapids, a mountain on the shore of Lake Nipissing, the Thirty Thousand Islands. Among the Innu, it dams Lake Pekuakami, Lake Saint-Jean; in the versions collected by ethnologists, it opens the Grande Décharge, empties the lake and flees toward the sea. Among the Maliseet (Wolastoqiyik), it is Gluskap who undoes the great beaver's works and leaves the Great Lakes behind him.2
An ethnohistorian proposed in 1972 that this be read as a distant memory of the Pleistocene's giant beavers. She herself framed the idea as a question, and those who have taken it up since still present it only as a hypothesis: the resemblance could be mere coincidence, and no Castoroides fossil is recorded in Quebec, the easternmost known in Canada being an incisor from New Brunswick. We will not settle the question. What is certain is that these accounts are alive: the Pekuakamiulnuatsh of Mashteuiatsh publish today their Mishtamishk, the great beaver who, pursued, goes down the Saguenay and reaches the sea. Some thousands of years later, it was from our own rivers that the beaver would disappear.
1The Pleistocene, from 2.6 million to 11'700 years before us, was the epoch of the Quaternary glaciations and their megafauna — mammoth, woolly rhinoceros, giant beaver. It closed with the extinction of most of them.
2Innu accounts: F. G. Speck, Naskapi. The Savage Hunters of the Labrador Peninsula, 1935, p. 110-114; D. Clément, Le bestiaire innu 1. Les quadrupèdes, Presses de l'Université Laval, 2012, chapter "Amishku," p. 43-68. Maliseet account and the fossil-memory hypothesis: J. C. Beck, "The Giant Beaver: A Prehistoric Memory?," Ethnohistory 19(2), 1972, p. 109-122, taken up by D. Delâge, "Du castor cosmique au castor travailleur," Les Cahiers des dix n° 68, 2014, p. 1-45 (open access on Érudit). Version told today by the community: La légende de Mishtamishk, Pekuakamiulnuatsh de Mashteuiatsh (new window).
The beaver was once a common and widespread mammal in Europe. Humans hunted it until the end of the 19th century and came close to exterminating it entirely. The Eurasian beaver survived only in a few regions: the lower Rhône, the Elbe, southern Norway, and a few rivers in Russia.
In Switzerland, the last native populations died out in the early 19th century. The value of its fur was the main cause of the intensive hunting — a decisive factor in its eradication.
The virtues attributed to its secretion, castoreum, also played a part in its disappearance. This musky ointment was believed to cure many ailments — not entirely wrong, since it contains traces of salicylic acid, with its analgesic properties. Its flesh was prized, its tail considered a delicacy. Classified as a fish, it could also be eaten during Lent. The beaver thus remained absent from our country for nearly 150 years.
Crepuscular and nocturnal, very wary, it can sometimes be observed in broad daylight if left undisturbed. Heavy, stocky build, light to very dark brown coat, small eyes and small ears.
No external trait distinguishes males from females. Only nursing females show two pairs of pectoral teats. Sex can only be determined by capturing the animal.
The beaver lives in the most varied aquatic habitats — evidence of its great adaptability. Territorial, it occupies 0.5 to 7 km of watercourse, depending on the food resources available.
It mainly frequents free-flowing or still fresh water that does not freeze over entirely in winter or dry up in summer. Its ideal body of water is 1 to 2 m deep, with a minimum depth of 60 to 80 cm. The banks must allow for burrow construction.
Along watercourses, it marks its territory with castoreum. Depending on the location, it digs burrows into the banks (submerged entrance, ventilation shaft). At our latitudes, it lives in simple burrows or burrows with a canopy, more rarely in lodges.
The beaver has always contributed to habitat dynamics. A true generator of biodiversity, wherever it settles it encourages the return of many animal and plant species.
Waterproof coat, multipurpose tail, webbed hind feet, orange-enameled incisors: every part of the beaver's body answers a precise demand of its semi-aquatic life.
Coat ranging from light to very dark brown, lighter on the belly. Covers the whole body except the tail. There are 12'000 hairs per cm² on the back and up to 23'000 on the belly — perfect thermal protection and waterproofing.
The animal's main distinguishing feature. 20 to 30 cm long by 12 to 16.5 cm wide, covered in leathery, seemingly scaled skin. Regulates temperature in summer, serves as a fat reserve in winter. While swimming, it acts as both rudder and propeller. When it senses danger, the beaver slaps the water's surface to warn others nearby.
Each foot has 5 toes. Front foot 5.1 to 6 cm, hind foot 9.5 to 17 cm, with highly developed webbing. The unwebbed front feet handle branches, mud and food with precision; the webbed hind feet are used for swimming. The second hind toe carries a split "comb" claw for grooming the coat.
The incisors grow continuously and are covered with extremely hard orange enamel. When felling, the lower incisors act as true wood chisels, exerting a pressure equivalent to a weight of around 80 kg.
More than 300 plant species are on its menu. Each day, a beaver eats a little over 1.5 kg of woody food. In autumn and until early spring, it feeds mainly on bark.
It generally feeds from a central point — its lodge or burrow. 75 to 83% of cuttings are made within the first four meters of the bank. The maximum distance it strays from the watercourse is estimated at 15 to 20 m (30 m at most).
The intestine reaches six times body length. Pre-digestion of cellulose takes place in the caecum. The beaver also practices caecotrophy — the re-ingestion of food pellets, common among herbivorous rodents.
The beaver eats more than 300 plant species — here are some of its favorite woody species. Botanical plates: public domain, via Wikimedia Commons & iNaturalist
Beavers live in family groups of five individuals on average: a monogamous pair, bonded for life, this year's young, and those from the previous year. The territory extends over 0.5 to 7 km of watercourse depending on food resources.
Mating takes place from January to March, in the water. Gestation lasts 105 to 107 days. A single litter per year, of 2 to 4 kits, born between late April and late June, weighing 500 to 700 g. Weaning at around two months. Sexual maturity at 18 months in males, 30 months in females. At two years old, the young leave the family to seek their own territory.
Smell is the primary sense. Castoreum carries a great deal of information: sex, age, health, and social status. Sight is less well adapted — but a silhouette against a light background is clearly recognized.
The living chamber sits above water level, kept dry. A territory often includes several lodgings — main and temporary — sometimes with multiple entrances. The typical structure:
The dams it builds can reach several meters in length. Height varies with the topography. It builds with trunks, branches, mud, and plant material.
The dam guarantees it a constant water level and eases the transport of food. Its functions, beyond housing:
Eases movement and food transport. Does not shelter a burrow and disappears with floods.
Protects occupied or temporarily occupied burrows. Well anchored, it does not disappear easily.
Always shelters occupied burrows. Solidly anchored and constantly maintained by the family.
The beaver gnaws trees at their base. It does not control how they fall — but the tree often falls toward the watercourse, convenient for transport. Typical signature: a pencil-point cut.
The beaver gnaws all the way around: two opposing cones meet and form an hourglass shape before the tree falls.
A long, smooth, oblique notch, beveled like the tip of a whistle.
The classic signature: the base, gnawed all the way around, tapers to a point, like a sharpened pencil.
Several angles of attack cross and trace a "K" on the standing stump.
Dams, gnawed trees, weakened banks: find out how to prevent and resolve conflicts, step by step — always in line with the law.
For beginners, telling them apart can be tricky, especially in the water. With a little attention, it becomes possible to tell them apart — and worthwhile, since the coypu is not a natural part of our environment.
Castor fiber — a natural inhabitant of our watercourses, reintroduced in Switzerland — first release in 1956, reintroductions continued from 1958.
20 to 30 kg for a body of 80 to 100 cm, flat scaled tail of 20 to 30 cm, webbed hind feet, exclusively vegetarian, crepuscular and nocturnal.
A South American species introduced to Europe around 1920 for fur farming. Escaped individuals gave rise to the current population.
Up to 10 kg for a body of 50 to 60 cm: noticeably smaller than the beaver.
The Centre Suisse de Cartographie de la Faune (CSCF) currently identifies no stable population in Switzerland — the species is spreading in the Lake Geneva basin and in Ticino, but only as isolated individuals.
Flat, broad, covered in scales.
Beaver tail · Tangopaso, Wikimedia Commons · public domain
Round and thin, like a rat's.
Coypu tail · © BeaverWatch
Compacted wood fiber, 3.5–5.5 cm. Rarely seen, as they are expelled into the water.
Beaver droppings · © BeaverWatch
Cylindrical with a pointed end, blackish-brown, 2.5–3.5 cm.
Coypu droppings · © BeaverWatch
Short muzzle, short whiskers.
Beaver portrait · © Roger Vilet
Long, very visible white whiskers, prominent orange incisors.
Coypu portrait · © BeaverWatch
Swims low: only the head breaks the surface, the back barely shows, and the flat tail stays underwater.
Swimming beaver · Sketch © BeaverWatch
Swims high: the head and the arched back break the surface, and the long, thin tail trails along it.
Swimming coypu · Sketch © BeaverWatchContent compiled by BeaverWatch from the following scientific and institutional sources — available from the association on request.
