DIADEMS AND DEW: GARDEN SPIDERS
After a week of high pressure, this morning the garden is drenched in October rain and the full extent of the takeover is there to see, picked out in glistening droplets. Every bush is festooned with the sagging geometry of webs, stretched out of shape by their dewy burden, a monument to the industry of the diadem or garden orb spider.
The time of Araneus diadematus has come. Walk down the narrow path and you’re an iconoclast, a web-buster, as silk strands tug at your clothes and feather your skin. The huge females, each as big as a blackcurrant, hang head-down at the centre of their masterpieces. A strong thread trailed speculatively into the night air has found purchase on a stout twig. Travelling down this bridge line the spider dropped vertically to create a Y-shape, which she framed by casting silk from her abdominal spinnerets. Adding more radial lines, later filled in with glue-slicked concentric strands, she eventually created the familiar circular orb web, held in position by stiff guy-threads, which can be over a metre long. By travelling down the non-sticky threads, she avoids being caught in her own trap.
In position at the hub, she is a femme fatale, her front legs resting on the key lines, which will telegraph the arrival of a victim. The hapless fly, moth or even wasp that blunders in, is quickly bundled in thick silk and injected with venom to anaesthetize it and break down its internal tissues. This allows the spider to suck up its contents through the cocoon, like drinking lemonade through candy floss. If the prey is too big or dangerous she will cut it loose from the web and neatly repair the damage. Each night she spins a new web, often eating the old one: orb spiders are diligent recyclers.
These females glow with autumnal colours; chocolate, orange, ivory and sand starred with a crucifix of white dots. Swollen with eggs, since spring they have moulted out of their exo-skeletons eight times, and are now at their largest and most impressive. Back in late summer, they mated. This is a fraught affair for the smaller male who must tweak the female’s web in just the right way to pique her interest without advertising himself as dinner. If he sends the right signals, he will be able to approach close enough onto the web to perform a bizarre ceremony. On his head, near his front legs is a pair of sensory organs called palps, the ends of which are swollen like boxing gloves. Before mating he spins a silken platform on which he deposits a drop of sperm. Dipping his palp into the liquid, he charges it much as we’d fill a fountain pen with ink. The next step is crucial. With ritual precision- a slapdash performance could mean death – he inserts his palp into her genital opening or epigyne. Mating over, a quick retreat is important: her post-coital trance will not last long. Older, weaker males often pay dearly. Even for the lucky ones, death is not far off as autumn chills approach.
The female spider continues web-spinning, until her eggs are mature and ready to be laid. In a cranny or under a dried leaf near her web, she creates a nursery of soft, dense silk in which the eggs will spend the winter, safe from predators. Guarding her enormous clutch is her last act and she will die soon. When the young spiders emerge en masse in spring, they huddle in small yellow balls among the vegetation. Disturb them and the ball explodes in all directions. Most spiders are anti-social to the point of cannibalism and so the spiderlings soon need to disperse, some through the surrounding leaves. Others wait for a warm day to climb to a high point such as a fence-top or a gatepost and stand on tiptoe, their abdomens facing upwards. They trail a silk thread which is caught by the gentlest breeze and lifts the spider into the air. This activity, known as ballooning, can take these wingless aeronauts skywards and spiders have been caught from aeroplanes several thousand metres up. It’s an effective way of colonising new territories, with the risk that your landing place is uncertain and you are likely to be snapped up by a passing swallow or swift. Even so, many find a new home, which explains why garden orb spiders occur on tiny roof gardens even in the centre of large cities.
Araneus diadematus is just one species among forty thousand. Spiders are soft, wingless and vulnerable, and it seems miraculous that they are such successful survivors. But survive they do. It’s been calculated by the great spider naturalist Bill Bristowe that an acre of meadow at certain times of year can be home to a million spiders, and that the weight of prey that British spiders consume each year is the same as the weight of all the human beings in England. Love them or loathe them, they are here to stay, an astonishing and superbly-adapted group of animals. Without them our gardens would not only be over-run with pests, they’d also be much less interesting places.
Brett Westwood October 2015
Maligned Species is a free poetry-writing project – to encourage poetry with a scientific slant.
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