There are 96 species of snakes found in Sri Lanka, with 5 being highly poisonous. The highly poisonous snakes are the Cobra, Indian Krait, Sri Lankan Krait, Saw scaled Viper, and Russell's Viper. These snakes can be deadly if bitten. In addition, there are 91 species of mildly poisonous or non-poisonous snakes. The document provides descriptions of the highly poisonous snakes and advises on preventing snake bites.