Bee orchid, ploughman's spikenard, viper's bugloss, wild basil, wild carrot, wild parsnip, wild strawberry, ladies bedstraw, yellow- wort, bird's-foot trefoil: these are some of the chalk grassland plants that are common to Box Hill.

Over a dozen species of orchid have been recorded, and at least 400 species of other flowering plants: as any as 30 or 40 different plants per square metre may be found in the botanically most important areas such as Juniper Top. Box Hill has long been a lure for entomologists like Richard Shields, who in 1856 described it as 'one of the most prolific localities in rarities both Entomological and Botanical, and embracing the most beautiful scenery with which I am acquainted.'

The most numerous insect is probably the yellow meadow ant, whose anthills are often an indicator that an area has been grassland for many years. There are also several types of bees and wasps, including wood wasps, and a number of interesting beetles such as the soldier beetle, the bloody-nosed beetle and the cardinal beetle. An invisible life is lived in these grasslands by many other invertebrates, not least the grasshopper and the large Roman snail, now becoming scarce. Wingless female glow-worms shine in the grass on summer nights; the males, which are winged, glow less brightly but sometimes fly into lighted rooms. But the show-stoppers are the butterflies:

Box Hill provides a habitat for a staggering 40 of the 58 British species, among them the common blue, the chalk hill blue, the Essex skipper and the marbled white. The adonis blue, which due to careful management has recently made a comeback, enjoys a remarkable symbiotic relationship with the yellow meadow ants and the horseshoe vetch: the butterfly lays its eggs on the vetch on warm south-facing slopes and when the eggs hatch the caterpillar produces honey dew on which the ants feed. In return, the ants protect the pupa and the caterpillar, taking it below ground where it turns into a butterfly - and so the cycle repeats itself. Centuries of light grazing have produced the extraordinary species-rich pastures of Box Hill. The North Downs were cleared by Stone Age people in about 4000 BC, when crops were planted and settlement patterns developed.

As arable farming became concentrated in the richer soils of the Weald, sheep grazing became common. From AD 500 onwards, until the end of the nineteenth century, shepherds grazed their flocks on the downland slopes by day and 'folded' them on the lower arable fields at night for enrichment by dung. In this way nutrient levels on the downland turf were reduced. And it is precisely because the downland is unimproved - in other words unfertilised - that it supports such a spectacular variety of plants (and therefore invertebrates and birds) without competition from dominant, fertility-loving grasses. The brightly coloured downland plants are able to co-exist in such density because each species has adapted to exploit the environment in a different way. Growing conditions are tough. Soils are poor and the exposed hills are at the mercy of the weather. Under pressure from grazing, parched in summer and frozen in winter, each plant must compete for water, minerals and light. These constraints prevent plants from reaching their full potential and a delicate balance is achieved in which no one species can dominate.