The Orb Spider - Nature's Wonderful Spinner
As summer begins to shade into autumn, hedges and banks become festooned with vertical, spirally patterned webs made by orb-web spiders. Each woven web may display its fat-bodied occupant clinging motionless and heads down, waiting for prey to blunder into the trap.
In autumn, the orb-web spiders reach full size and maturity, having spent the early part of the summer making ever-larger webs as they increase in size by shedding their outer skin (cuticle). Their large September and October webs seemingly appear overnight on almost every bush, bank, hedge, a tuft of grass and group of flowers. If you cannot find the spider itself sitting in the centre of its web, it will probably be lurking in its lair, which may be a folded leaf to one side of the web waiting for its victim.
Autumn Watercolour Artwork by Alison Langridge
The most familiar orb-web builder is one of Britain's largest spider species. It is the garden cross or diadem spider Araneus diadem so-called because of the white crucifix like pattern on the top of its abdomen, the ground colour of which varies from pale brown to reddish-brown or sepia. Common in gardens along thick hedgerows and clearings, the web occupants are generally females with bodies as big as a large pee. Adult male diadem spiders are recognisable by their smaller, triangular abdomen and prominent palps or mouth fingers. After maturing, the males abandon their webs and spend their short lives visiting those webs occupied by females.
Courtship and mating are with extreme caution among diadem, and other orb-web spiders, for the short-sighted female, is liable to attack all intruders even when it happened to be one of her species. Approaching the female's web, the male announces his presence by tweaking an outer strand of her web. At the same time, he provides himself with an escape line of silk if she rejects him and wants to eat him for her supper. The female may fiercely chase him away several times before the female responds to the particular vibrations induced by his web pulling. Only then will mating occur. Mating itself takes place employing the male's pulps. Before the actual sexual encounter, the male discharges semen onto a special silk pad and then fills each of his palps with seminal fluid. He then inserts the first one and then another palp into the female spider's genital aperture called the epigyne. Depending on how aggressive the female is, he may need to retreat before attempting the risky endeavour again after the first insertion. When the mating is over, the male retires before seeking out another female. Many males, however, do not survive for more than one mating. Others die of starvation, predation or being killed by the female.
Egg laying and hatching
Some weeks after insemination, the female leaves her web and seeks out a hiding place where she produces several hundred eggs which she covers with a double layer of yellowish silk. She hides the cocoon in a safe place, such as beneath tree bark. She may even use the corner of a garden shed. Here the eggs overwinter before hatching the following May.
Initially, the spiderlings are very small, with their abdomens scarcely as big as a pinhead. Distinctively coloured in a rich yellow, they have a short bar of dark brown at the rear of the abdomen.
The spiderlings occasionally attract attention by their habit of congregating in a tight ball on the base of silk. If you touch the ball with your finger, the tiny spiders scatter. The spiderlings remain in their ball until the following moult, then dispersed to make small individual webs of their own. Each spider may come to maturity at the end of its first summer but more usually take another year. They die soon after mating and egg-laying. However, that usually depends on the weather and the food supply.
Trapping prey in the web.
Spiders usually construct their webs in the evening or the early morning hours, commonly positioning them about 30 to 60 centimetres from the ground to secure a steady stream of prey at a vantage point. In gardens, they take a heavy toll on insects such as craneflies and daddy long legs whose low blundering flights made them especially prone to ensnarement. Even grasshoppers are caught, but the spider generally cut loose the more violent or unpleasant tasting insects.
Only the larger outer spirals of the orb-web spider's web are sticky (viscid), and it is the main region that traps the blundering insects. If the spider is lurking in her lair, it is given immediate notice of the victim's arrival through a line of silk connected to the spider's forelegs. The spider then dashes across the web to bite the prey injecting it with venom, which contains a digestive enzyme to break down the insects' tissues into liquid form, which the spider drinks. At the same time, despite a swathe the captive in silk so it is powerless and can be stored for future use
Despite its apparent delicacy, the spider's silk is extremely strong and elastic. Six spinnerets, special organs situated at the hind end of the abdomen produce the silk. Each spinneret excludes silk in multiple strands that, by chemical reaction, coalesce and solidify as one strand as they leave the body.
The role of spiders in controlling the insect population is significant, but spiders themselves are not without enemies. Birds eat them, and many spiders are preyed upon by robber flies, ichneumons and hunting wasps, and other spiders.
Other Garden Spiders
Garden spiders belong to the family Argiopidae, of which there are about 40 species in Britain. They all make orb webs, but few are as large and conspicuous as the diadem spider's fabulous constructions.
One of the more secretive species is the vast, sinister-looking Araneus umbraticus which builds its web on old trees and outbuildings. Mottled brown or near black with a subdued credit crenellated pattern on its flat and somewhat dimpled abdomen, this spider spends most daylight hours in a crevice near its web emerging at night to kill and collect pray. This spider hibernates in winter.
Araneus quadratus is another large related species commoner and heathland in northern England. Its variable-coloured abdomen bears a dotted pattern in the rough form of the rectangle.
Many other off spiders are much smaller, notably those of the genus Meta. Meta segmentata is a typical example. Often spinning on low vegetation gardens, its web has a clear space in the centre, and it's usually set to a slight angle to the ground. Equally distinctive is all the web spun by the two commoner species of Zygiella. Each is identifiable by the emission of spiralling from two upper segments of the web.
Orb Spider Web Construction
All orb-web spiders begin their web with a horizontal bridge line. A thread is secured at one end while the other is allowed to waft across space until it adheres to a twig or leaves; the spider strengthens this bridge by passing over it several times. She does this by laying down more silk. Next, the spider passes from one end of the bridge to the other, dragging a loose thread and fixing it at both ends. She then returns to the centre of the thread and descends on a different line, which is fixed to an outer point after being pulled taut. The spider has created the first three web radii and one frame segment in the form of a closed letter Y, the centre of the Y forming the web centre.
Further frame lines make a multi-sided frame after each addition. They are constructed by repeated climbing and dropping; as many as 40 radii are produced. She is next, completing the central hub with inner strengthening spirals. Leaving a gap, the spider constructs the main outer web spiralling, using radii as footholds, but only as a temporary measure. Finally, the spider goes over the primary spirals again, destroying them as she goes and replacing them with gum coated lines that will secure the prey. Oil on the spider's feet prevents her from being caught in her web.