Silver-studded blue
The dazzling silver-studded blue is a rare butterfly of heathland habitats, mainly in southern England. It has undergone severe population declines in recent years.
Silver-washed fritillary
The silver-washed fritillary gets its name from the silver streaks on its underside. It is on the wing in summer, preferring sunny glades in woodlands. Despite declines, its range has spread over recent years.
Silverfish
The silverfish is so-named for its fish-like way of moving and its silvery scales. It can be found in the damp corners of the house, such as the kitchen or bathroom. Infestations can cause serious damage.
Silverweed
As its name suggests, Silverweed has silvery leaves with toothed edges. It can be found in grassy places, along roadsides and on waste ground - look for yellow, saucer-shaped flowers and red runners.
Siskin
An attractive, green-and-yellow bird, the siskin regularly visits birdtables and feeders in gardens. Look for the bright yellow barring on its black wings, and the black crown of the males.
Sitka spruce
The Sitka spruce was introduced into the UK from North America in the 19th century. It has been widely planted as a forestry tree; look for classic needle-like leaves and pale brown, domed cones.
Six-spot burnet moth
The six-spot burnet moth is a day-flying moth that flies with a slow, fluttering pattern. Look for it alighting on knapweeds and thistles in grassy places. It is glossy black, with six red spots on each forewing.
Skullcap
The delicate, tube-like, violet-blue flowers of Skullcap bloom from June to September in damp places, such as marshes, fens, riverbanks and pond margins.
Skylark
The song of the skylark has been the subject of many great musical and literary works. A quintessential feature of our farmland and grasslands habitats, it is declining rapidly with habitat loss.
Slavonian grebe
The rare Slavonian grebe is an attractive diving bird with distinctive, golden ear tufts that give rise to its American name - 'horned grebe'.
Slipper limpet
These non-native limpets arrived from America in the 19th century and are now widespread in the UK. They form stacks and have a specially adapted shell which, when flipped upside down, looks like a slipper!
Slow worm
Despite appearances, the slow worm is actually a legless lizard, not a worm or a snake! Look out for it basking in the sun on heathlands and grasslands, or even in the garden, where it favours compost heaps.