At the end of an exceptionally warm month, with barely enough rain to dampen dusty footpaths, I half expected this little spring-fed mire might have dried up. But there it was, reassuringly squelchy, with its bright green cushions of sphagnum moss. Never underestimate the capacity of this bog-builder to hold on to water in dry summers; its leaves are living sponges.

From the bottom of the slope, you would never guess this bog existed, tucked in among the bracken, sedges, rushes and withered bell heather. But walk uphill and the orange, spear-shaped seedheads of bog asphodel, trooping alongside a trickle of water, give a clue that the ground will soon be treacherous underfoot.

It took a while to find my quarry, the round-leaved sundew, Drosera rotundifolia, which I first saw here almost half a century ago. This carnivorous plant, its leaves smaller than a five pence piece, grows on sphagnum, but this late in the season, its rosettes can be half submerged by rampant moss growth. Resigned to an afternoon with wet knees, I knelt for a closer look.

And there they were, leaves protruding through the moss, like ruby-red outstretched palms of a drowning victim, fringed with hairs whose ends seem to be tipped with glistening nectar. They are temptation for an insect about to make a fatal mistake: they are loaded with sticky mucilage and powerful enzymes. Death traps.

Unfortunate prey – mostly mosquitoes, springtails and small beetles – was firmly glued and would soon be digested, leaving only empty exoskeletons. Among them, a long, single leg: a cranefly had escaped death by shedding a limb. Flies of all sizes swarm here on warm afternoons and this sundew population is well fed. Most had seed capsules, easily broken open to release seeds that are as fine as dust, carried away on the wind.

To anyone who drives across the north Pennines, the treeless moorland landscape of heather and rough grassland can seem a bleak, barren prospect, but there are countless little biodiverse oases like this wherever spring water bubbles to the surface. Wet knees are a small price to pay to appreciate their beauty.