In early April, when the chiffchaff sings its drab little song in the leafless hawthorns, something is stirring in the dead bracken. Having spent the winter months underground, one of our most fascinating creatures slithers into the weak spring sunshine: the adder. The emerging adders haven’t eaten for six months, but food is not on their minds; it is the mating season. Rival males indulge in spectacular ritual combat, rearing up side by side and twisting and wrestling at great speed. After mating the snakes disperse and spend the summer in solitary pursuit of mice, voles, lizards, frogs and fledglings. Adders never use more energy than is necessary and spend a lot of their time basking. These living solar panels get a great deal of their energy directly from the sun, and so efficient is their metabolism that they only require six to ten meals a year.