Thursday, September 1, 2016
Quarry life in early autumn
Today's Guardian Country Diary is about autumn gentians and heather bees in a Weardale quarry.
Weardale is a valley full of old mines and quarries, mostly legacies of the lead industry and quarrying of the Great Limestone. Most of these are now worked-out or abandoned, like this one near Hill End at Frosterley.
From a distance it looks a bleak place, but when you take a close look there are some fascinating plants and animals here.
The bottom of the quarry is flooded, with a shallow lake and islands in the centre, surrounded on the north side with weathered rock spoil tips ...
..... and the vertical rock walls are being colonised with plants and even rowan trees.
In autumn the thin turf that covers the weathered spoil tips is covered with a tapestry of small flowers, like this eyebright and ground ivy .....
.... and this wonderfully fragrant wild thyme. Everything that's more than about one inch high is grazed off by rabbits, except for ....
... a fabulous display of autumn gentians Gentianella amarella.
Rabbits must find these distasteful because in late August there are thousands of them in flower, unmolested.
The short calcareous turf, well-drained and with most of its nutrients leached away by rain, seems to suit this delightful little plant.
The quarry's other autumn speciality is its colony of heather bees Colletes succincta. These little bees are slightly smaller than a honey bee and each digs its own nest tunnel in the terraces of earth that build up where sheep make regular tracks across the spoil heaps. The bees excavate individual tunnels, where they lay their eggs and provision them with heather pollen, but they nest colonially.
This colony has several hundred individuals, whose nest tunnels are sometimes just a few inches apart.
Smart-looking little bees, with their ginger furry thoraxes and striped abdomens.
These bees are only around for about 3-4 weeks in late summer, when the heather comes into bloom. Their first priority is to mate and the males patrol just a few inches above the ground, intercepting the females when they come within reach. Sometimes several fall to the ground, locked together in a ball of wings and legs.
After mating the bees shuttle backwards and forwards to the heather moorland, in this case several hundred metres distant, to collect food to feed their brood when they hatch from the eggs, then cap the tunnels. Autumn rain washes away their little spoil heaps of excavated soil and all trace of them disappears.
Just a few weeks in the sun, then the rest of their life cycle is spent underground.