Spider webs

Different groups of spiders build different types of webs, depending on the type of prey they capture and the location of the web.

Web of the comb-footed platform spider

 © Australian Museum

Types of webs

Gum-footed web: Redback Spider

Redback Spider webs consist of an irregular upper silk network with a closely woven, thimble-like retreat. From this upper network, vertical sticky catching threads run down to ground attachments (the 'gum-feet'). The webs can be built in a variety of places, such as among logs and rocks, grass tussocks and broad leafed vegetables, under flower pots and garden furniture, in outside toilets, sheds and junk-piles. The upper retreat network is usually built in dry, sheltered areas away from sunlight, while the sticky catching lines run down into open, more exposed areas. Insects, spiders, even small lizards that walk into the 'forest' of sticky lines are held by them while the spider races down to deliver a quick bite and then cover the struggling prey in bands of sticky silk. These swathing silk bands are pulled rapidly from the spinnerets by a row of serrated bristles on the ends of the last legs - the 'comb foot'.

Each vertical sticky line is made up of four dry supporting lines covered with a row of sticky droplets. The lines each have a weak ground attachment. The support lines provide strength and are under tension. When an insect walks into the array of sticky threads, its struggle breaks the lines at their weak attachment points and the lines contract upwards, lifting the prey off the ground and reducing its chances of escaping. The sticky silk comes from the wide pair of spigots on the larger posterior pair of spinnerets. Their wide mouths also allow the Redback to rapidly 'comb' out copious swathes of sticky silk over the struggling prey, thoroughly entangling it. This method of prey capture is used, not only by Redback Spiders, but by most other spiders in the family Theridiidae, the comb-footed platform spiders.

Platform web: Comb-footed platform spiders

The comb-footed platform spiders, such as Achaearanea mundula, are related to Redback Spiders (Family Theridiidae). They are not dangerous and their web is quite different from that of Redbacks. They are common in bushland and gardens in eastern Australia. The female spider is 5 mm - 8 mm long and has a subtle 'patchwork' colour pattern, ranging from yellow and reddish browns to black.

These spiders are best recognised by their moderately large and complex webs, which have a network of threads above a silk sheet (the 'platform'). When insects fly into the 'knockdown' network of threads they fall through onto the silk sheet below, where they are seized by the spider. The spiders often use curled leaves or some leaf fragments to make a loosely silked retreat which is placed in the centre of the knockdown network. The egg sacs are placed inside the retreat. These webs are usually built among understorey shrubs and low trees and are often seen in overgrown gardens.

These complex webs harbour a range of other animals, from small moth larvae that scavenge along the silk lines, to spiders that find prey in the outer parts of the web. Some of these are small prey stealers belonging to the genus Argyrodes. However, they include one species, Argyrodes incursus, which is a specialist predator on the Achaearanea mundula. It is a small, jet black spider with a single red spot on its abdomen. Somehow, the smaller spider kills the larger spider and eats it. The diminutive killer then takes up residence inside the Platform Spider's retreat, using it as a shelter for its own egg sacs.

Orb webs

Orb webs have developed as an efficient means of capturing flying insects. Their structure provides a unique combination of large capture area with near invisibility, making detection and avoidance difficult, especially at night. Only when the web is covered with dew is it clearly visible. Orb webs also need relatively little silk to build and they can be completed quickly. This is important because, while Nephila webs are 'semi-permanent' (repaired before being taken down and re-made), many nocturnal orb weavers, such as Eriophora, destroy and eat (recycle) their webs toward dawn and must rebuild them each night. This recycling process is very efficient as it returns the silk protein to the silk glands to make new silk.

It takes an orb weaver about 30 to 45 minutes to make its orb web. Air currents are used to waft the initial silk line extruded from the silk spinning organs (spinnerets) across a gap in the foliage to entangle in leaves or twigs on the other side. The spider moves back and forth across this bridge line, strengthening it by laying down more silk. It then drops from the bridge line's centre to attach a vertical line to the ground. This provides the basic Y shaped framework to which are then added supporting outer frame-lines, and the radial lines (the 'spokes') on which the spiral lines are laid. A non-sticky, temporary spiral line is laid down first, starting from the centre and running outwards. This temporary spiral gives the spider a 'scaffolding' from which it then lays down the more closely spaced, permanent, sticky spiral, starting from the periphery toward the centre or hub. The spider removes and rolls up the temporary spiral as it lays down the sticky spiral. The excess silk is eaten and recycled.

Juvenile webs: St Andrew's Cross Spider

The young of the St Andrew's Cross Spider make a silk emblem that is quite different from the 'diagonal cross' of older spiders. At the centre of their small orb webs they lay down a circular lace-like pattern of zig-zag silk bands, on which the spider sits. This silk pattern may also attract small insects to the web but, in addition, it provides a most effective defense against predators. When disturbed the spider simply disappears, a trick it achieves by slipping rapidly through the web spiral and onto the other side of the silk pattern. A lace-like pattern in the web's centre is typical of both young and adults of another common species, Argiope trifasciata, which has a distribution encompassing much of Australia and the western Pacific region.

Horizontal Line webs

A number of unrelated spiders use single line webs, strung either horizontally or at an angle, to catch their prey.

Phoroncidia sp. (Family Theridiidae)

These tiny spiders are found on low vegetation, bark and leaf litter. They spin their short, simple line of sticky droplets across a space and sit in wait, with a front leg holding the line. Small insects, especially flies, either hit or attempt to land on the sticky line (some flies rest hanging from dry spider silk lines) and become stuck.

Miagrammopes sp. (Family Uloboridae)

The cribellate spiders of the genus Ranguma, also have a single line web. These stick-like spiders keep their single woolly silk line taut by pulling any slack silk into a loop underneath their body. When an insect hits the line of wool-like cribellate silk, the spider releases the loop of silk which whips along the line to help tangle the prey.

Bolas Spider webs

The Bolas Spiders are descended from orb web weaving ancestors. By greatly modifying their web they have evolved a unique method of hunting.

At night, these spiders emerge to hunt male moths, which are their only prey. To do this, they sit on a horizontal line and spin a short, single vertical line with a large dollop of sticky silk on its free end. This line hangs from a leg down into an open space among the foliage, much like we hold the line over our fingers when fishing to feel for fish bites (another common name is the Angling or Fishing Spider). While the spider sits and waits it is exuding an air-borne scent (pheromone) that mimics that used by female moths to attract males. When male moths fly in towards the spider, attracted by this false scent, the spider senses the vibrations of their wingbeats through her long sensitive hairs. She then starts to swing the sticky bolas in a circle below her. The moth flies in closer and is hit by the bolas and covered in sticky silk. Coiled 'reserve' silk within the bolas is paid out as the spider 'plays' the moth, preventing the line from breaking. Soon the spider pulls the moth in, bites it and begins feeding on it.

The bolas line can be regarded as a highly modified remnant of an orb web.


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Dr Mike Gray , Senior Fellow
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