Spiders use silk in their reproductive process. All spider eggs are wrapped in silk and the male uses it when transferring sperm to his palps for mating. The use of silk for web-weaving evolved from the opportunity to catch insects which had evolved wings for flight during the Carboniferous and Permian periods.
Cobweb weavers were the first of the weavers. These spiders build horizontal lacey sheets of web, often close to the ground or on large surfaces like tree trunks. The cobweb weaving spiders work from a tube-like retreat, racing out to trap insects falling on the sheet or, in the case of comb-footed spiders like the redback spider, trapped by sticky lines to the ground. Over time, weavers have developed a wide array of webs.
The webs of some weavers are large, seemingly messy, three-dimensional structures - some appear to have multiple horizontal layers. Other spiders produce two-dimensional wheel-like webs with radiating support spokes connected up with a spiral of silk. Spiders can build webs very quickly and efficiently, often using many metres of silk and numerous junction points.
The golden orb spider (Nephila pilipes) gets its common name comes from the colour of its large web. The yellow colour of the web attracts insects. The golden orb spider makes a permanent, strong web measuring one metre in diameter, strategically placed in flyways between trees. The large strong web may take as little as 20 minutes to build, even though it involves over 1500 junction points and requires 10-30 metres of silk. The design of the web allows the slightest vibrations to be transmitted along the web to the spider which usually sits in the centre of the wheel-like web. Even small birds and insectivorous bats sometimes get tangled up in it.
The females of the golden orb spider reach an imposing 45mm body length but they are basically harmless. Like many of the larger web-building species, these spiders tolerate other small species of spiders cohabiting in their web in a kleptoparasitic relationship (in some cases, the smaller spider feeds at the mouth of its giant host). Commonly encountered in the Wet Tropics and across northern Australia, the golden orb can also be seen around buildings.
You are more likely to see the black house spider (Badumna longinqua) around your home or resort than you would out in the forest. This medium sized, stocky black spider has a messy web with one or more entrance funnels through which the spider can be seen during the day. Moths are the favourite food of the house spider which has the good sense to position its web strategically in the corners of windows or under eaves or awnings. If you want to rid your windows of this spider's untidy web, please do so carefully with a broom so as not to invoke a bite. Although it is not sufficiently toxic to cause permanent harm, you will remember the pain for quite some time and you may experience other unpleasant side effects.
Another spider of impressive bulk is the furry-looking garden orb spider (Eriophora transmarina). A tell-tale indication of this species is that the upper portion of its legs are devoid of hair, having instead exposed maroon shiny skin.
Every night at dusk, this spider emerges from its daytime resting place on a nearby tree or shrub and creates its meticulous web in about an hour's time. By morning, the success of its feeding is evidenced by the breaks in the connecting threads. As the sun rises, the garden orb eats all of its web except for the anchor lines. These will remain in place throughout the day to provide the foundation for the next night's weaving. These lines are not sticky but are so strong that a person bumping gently into one will not break it unless a little force is applied.
The garden orb hangs its large web vertically in the flight paths of insects. As soon as the prey has touched the sticky web, the spider rushes out to bundle it in silk, spinning the meal round and round as it dispenses copious amounts of silk. From there, the victim is carried to the centre of the web and eaten straight away or hung nearby for later. Despite its fearsome appearance, the garden orb is relatively harmless and might even vacate the web if it is sufficiently threatened. Its bite is not thought to be particularly dangerous, but can be painful.
The strange little spiny spider (Gasteracantha fornicata) has the distinction of being the first spider in Australia collected by Captain Cook's crew. It is an unmistakable spider with a colourful hard outer shell painted in vibrant yellow, horizontal stripes against a deep maroon background. The small six to ten millimetre body and very short legs are also maroon. A total of six spines protrude from the sides and bottom end of the 'shell' and this seems to dissuade birds from making a meal out of them.The common name derives from the Latin name for arch (its abdomen is arched).
Commonly seen in the forest or in your backyard, the spiny spider is not toxic but has a sharp bite. Its web is usually not far from the ground, often being attached to shrubs or fences so it is an easy spider to find.