Country diary: across the hillsides of heather, the fallen parachutes of spiders
It is a perfect day to be an aeronaut in the Lake District: bright and beautiful but with a steady breeze. A paraglider is spiralling high over the Vale of Keswick, well above the height of the felltops. A slight haze blurs the more distant fells into blue silhouettes, but on a clearer day, the views at that altitude could stretch from the Mournes to the mouth of the Tyne.
We crunch up a slaty path on Hall’s Fell, aiming for the summit of Blencathra, but a glint of something silvery draws my eye. The reefs of heather blanketing the fell are still flowerless and winter-dull, but they are garlanded with ghostly threads, which catch the sun to reveal a glossy shimmer.
It seems likely the threads are, at least in part, the fallen parachutes of spiders. Many smaller species of spider (such as Erigone atra) are able to achieve flight by using strands of gossamer silk to lift themselves into the air – a process known as ballooning. Watching for a while, I see small insects flitting above the surface of the heather, and I briefly find a spider clinging to the wiry, woody tip of a shrub, as if ready to go.
Often – but not exclusively – undertaken by newly fledged spiders, ballooning is an extremely effective dispersal method, despite its high mortality rate. Research has proved that spiders can achieve takeoff even without wind by sensing and harnessing currents of atmospheric electricity.
Ballooning can take spiders just a few short metres, but it can also whisk them up into jet streams; mariners, including Darwin, have reported the creatures landing on ships hundreds of miles out to sea, and arachnids have been found in atmospheric samples collected three miles in the sky. Spiderlings have been known to survive for almost a month while travelling in jet streams, and many ballooning species also have adaptations to float on water and survive rough seas.
I take a moment to consider these high-altitude aviators; these riders of wind, water and electric currents; these spinners of worldwide webs. Then I resume my steady plod to the summit.