The Adder is relatively small (up to 75 cm long) brownish-greyish snake. It is easily distinguished by a dark zikzak line on its back. Sometimes it is reddish-brown and blackish, seldom entirely black.
Its favourite living places are mixed forests, edges of forests, cut-over areas, bogs, coastal areas of lakes and rivers with grasses. It also occurs in meadows and dry pine-groves. The Adder is widespread in Estonia but the density of it is various - in favourable living conditions they are numerous whereas they can be absent in large territories around this place. The Adder is a very settled animal, it moves around its living place for 60 - 100 metres. It hides in burrows of other animals, rotten stumps and all kinds of splits. Although they like to warm themselves in sun they are not very active in the day-time. They start to hunt at dusk and they are especially active during the first hours of night.
After successful hunt they will not leave their hiding place for two or three days.
The Adder mainly feeds on mice, frogs, newly hatched young birds, lizards and blindworms. Young adders eat insects, slugs and worms.
The Adder hibernates under frozen land in the depth of 0.4 - 2 metres where temperature will not be lower than 2 - 4 °C from September or October till April. They use the burrows of rodents, land under hay-stacks or heaps of stones. Adders are conservative as to wintering and they hibernate in the same place for years. On the first spring days after waking up male adders try to find the places of maximum warmth - they lie on warm land, fallen logs or warm stones in bright sunshine.
Wedding ceremonies take place 2 - 3 weeks or a month after waking up from the middle of May to the beginning of June. Adders' wedding dance is a complicated ritual. The partners lift up half of their body and joggle slender bodies towards each other. The Adder is viviparous, the eggs develop and hatch in the body of the female adder. Approximately ten little adders (16 - 18 cm long) are born in August. They are able to reproduce at the age of five years when they are at least 50 cm long. The life span of the Adder is 14 - 15 years.
Adders try to crawl away when humans come into their direction. They bite only when stepped on or tried to take in hands. The Adder is under protection. There are less and less suitable living places for adders due to cultivation of land.