These are lizards that have lost their legs, enabling them to slide through grassland and hide underground in narrow tunnels. Apparently, they are principally nocturnal hunters, favoured prey being slugs and the like, but I would guess insects as well. They give birth to live young (although technically they are inside an egg sac). Over winter they hibernate down in tree roots. Palentological studies show slow worms go back some 40-45 million years at least.
They keep growing throughout their lives, so size is an important indicator of age. Adult slow worms grow to be about 50 cm (20″) long, and can live, apparently, up to 30 years in the wild. The female often has a stripe along the spine and dark sides, while the male may have blue spots dorsally. Juveniles are gold with dark brown bellies and sides with a dark stripe along the spine, and are initially around 4cm long.
At Wilwell virtually all the slow worms recorded in the past four years are young adults circa 15 to 25 cm in size, including some believed pregnant and the odd one re-growing a lost tail. The tail can be discarded to distract a predator. We have seen the odd one that was clearly juvenile including one that was nowt but an orange bootlace (I would guess born that year). But we have only ever recorded one really old specimen estimated at around 35 – 40 cm. Why the dearth of older creatures? – well one thought is the local badger sett, as badgers relish worms and you might expect them to also take slow worms, and I would guess foxes would too.
Slow worms are known to frequent gardens, so if you see what looks like a very small snake it is almost certainly a slow worm.