Adder

There are three species of snake in Sweden: the adder, the grass snake and the smooth snake. Only the adder is dangerous to humans, although the others can also bite.

The adder can live further north than any other snake, and is found in almost all of Sweden, except up in the mountains above the tree line.

Zigzag pattern and vertical pupils

The adder has a large, triangular head, and its tail is much narrower than its body. Males are usually grey with a black zigzag pattern along the back. Females are often brown or yellowish, with a darker zigzag pattern. There are also completely black adders that resemble grass snakes, but grass snakes almost always have a yellow patch on each cheek.

Another way to distinguish between adders and grass snakes is to look at their eyes. If the pupil is round, it is a grass snake, if it is narrow and vertical, it is an adder.

Body temperature follows the air temperature

Snakes are poikilothermic (commonly referred to as ‘cold-blooded’), meaning that their body temperature follows the air temperature. Dark bodies mean that they can be more easily warmed by the sun. Adult adders usually grow up to 65 centimetres long, but the longest adder recorded in Sweden was just over a metre long. In the spring, they spend three or four weeks basking in the sun and maintaining a high body temperature. The males then shed their skins, after which the breeding season begins.

Eats small rodents and lizards

Adders play an important role in nature, eating creatures including voles and mice. Their diet consists mainly of small rodents, but they can also eat lizards, frogs and young birds.

Smells with its tongue

A snake moves its forked tongue continuously to pick up scents from the air and water. The snake’s sense of smell is located in the roof of its mouth. Different levels of odour particles on the two tips of the tongue tell the snake where food and danger are.

Hibernates all winter

Adders can be found in different types of habitats, such as mossy ground, the edges of forests, road verges, and the edges of meadows and fields. They avoid dense forest, as they need a lot of sunlight.

Adders hibernate throughout the winter beneath the frost, in holes in the ground or in among rubble. A large number of snakes can hibernate in the same place, with up to a hundred snakes gathering in some places. They emerge in the spring, warm themselves up in the sun and shed their skins. Snakes shed their skin in order to grow. You can sometimes find the dry, empty skin on the ground around its hibernation site.

Eggs hatch inside the female’s body

After hibernating, they mate and then move on to their hunting grounds, which may be several kilometres away from their hibernation site. A pregnant female does not travel very far. Her eggs are warmed and hatched inside her body, and in August she gives birth to a dozen or so young, called snakelets.

Most likely to spot adders in the spring

The adder is the first Swedish snake to appear in the spring, and you are most likely to spot an adder in the spring sunshine when they have just emerged from their hibernation. Look for rocky, sunny southern slopes where the snow thaws early. Gravel ridges and boulder fields with large rocks and many holes make for good hibernation sites. If you are lucky, you may see many snakes basking in a small area. Later in the summer, adders are harder to find. They then move on to beaches and wetter ground. Adders are good swimmers, slithering at high speed along the surface of the water.

A protected species

All snakes are protected in Sweden. In the past, however, it was common to kill adders. School classes would go out to kill snakes on outdoor activity days! Today, however, we think differently. If you find a snake on your property, you have the right to catch it and release it a few kilometres away. Snakes have a fear of open spaces, so if you don’t want snakes on your property, keep the grass short and leave open space around the house.

The adder is classified as ‘Least Concern’ on the Swedish Species Information Centre’s red list.