The heads of beavers, large rodents known for building dams, are their own kind of highly complex dam structure, with various retractable walls that let water in or keep it out. They can close valves in their nostrils and ears and a special membrane over their eyes; their epiglottis, the flap that stops water entering the lungs, is inside their nose instead of their throat; they use their tongue to shield their throats from water; and their lips to shield their mouths – their lips can close behind their front teeth. Their teeth are rust-orange, because they are strengthened with iron.
Their back feet are webbed like a duck’s; on land, their front feet act like hands, digging, grasping and carrying things from the riverbed to the surface – rocks, for example, tucked under their chins and cradled by their arms. When they swim, they do so while holding their front paws to their chests, like a severe governess in a Victorian novel, or a child pretending to be a rabbit. They prefer to carry branches in their teeth, like dogs. The biggest beavers weigh 50kg.
Beavers are monogamous. The males have a bone in their penis. Beaver kits are born with their coats, and mew, squeak and cry to get attention. Adults, to get attention – mainly to warn other beavers of danger – will slap water with their tails.
Their tails – which they tend to sit on like a saddle, between their legs – were once a European delicacy. The Catholic church, believing that beavers were half animal, half fish, designated that half as an appropriate food for lent. The naturalist Pierre Belon described the taste as like a “nicely dressed eel”.
In the Divine Comedy, the pilgrim Dante is in the seventh circle of hell (Violence) and compares the presence of a Geryon – a dragon-like monster with hairy arms and the “face of a just and honest man” sitting at the edge of the abyss that will carry him down to the eighth circle (Fraud) – to a beaver (il bevero), which moves between water and land:
As boats will sometimes lie along the shore,
with part of them on land and part in water,
and just as there [...]the beaver sets himself when he means war,
so did that squalid beast lie on the margin
of stone that serves as border for the sand.
Beavers have, in fact, played an important, if unwilling, role in several violent wars. The beaver fur trade was at the centre of the Beaver or Iroquois wars, King William’s war, and the French and Indian war. Beavers themselves are fairly comfortable with conflict, once the terms have been established. They behave in a way described as the “Dear enemy” phenomenon, where they will stop fighting with neighbouring territorial animals once their boundaries are set.
In some ways, they have established this relationship with us. Beavers have, several times, ignored humans and simply got on with it, in a way that has benefited us hugely. Recently, on a river south of Prague in Czech Republic, where government negotiations to build a dam had been delayed, a group of beavers went ahead and built several dams themselves, saving the government more than a million euros in construction. The wetland the beavers created was twice the size of what the government had planned.
Beavers build dams because creating deeper bodies of water allows them to build homes – called lodges – that can be accessed by swimming underneath the entrance. This stops predators who can’t swim from being able to chase and eat them. They start with layers of mud and stone plugged with grass and other softish green things. Then they put sticks and branches on this layer, facing upstream. These are held in place with more mud and stone, and any remaining holes are plugged with more vegetation. They carry mud in their paws, or bring water weeds up to the surface by scooping them up with their heads and noses. They look so proud, adding materials to the wall.
Beavers build such good dams that they are now being intentionally introduced to areas where these would otherwise be built by people. They change the way water moves through a landscape, preventing flood and drought, creating ponds where certain species thrive.
They do all this while eating only plants. In summer, water lilies, rushes, sedges and grasses. In winter, bark and wood from only the prettiest trees: aspen, dogwood, willow, alder and birch. They shit sawdust.
Helen Sullivan is a Guardian journalist. She is writing a book for Scribner Australia
Do you have an animal, insect or other subject you’d like to see profiled by this columnist? Email helen.sullivan@theguardian.com
