Spectacular spiders of the Wet Tropics

Skyrail Nature Diary: January 2011

Spiders are spectacular creatures with many unique qualities. Although the thought of a spider may make you quiver, they are often misunderstood and provide much value to rainforest ecosystems.

All spiders have the following characteristics: four pairs of legs; two body parts (cephalothorax and abdomen); fangs that move sideways and inject venom; spinnerets on the end of the abdomen (the silk producing organs); eyes that consist of small ocelli rather than compound eyes (six or eight).

Despite being able to produce silk, not all spiders make webs. Huntsmen, Wolf Spiders, Jumping Spiders, Lynx Spiders, Crab Spiders and Camel Spiders are all examples of roaming spiders that don't make webs.

Spiders have fantastic jumping ability. They don't keep their blood in vessels like we do, which allows them to use hydraulic pressure in their legs to launch themselves. A spider's legs have a valve where the leg meets the body. When the valve opens, the leg is forcefully pushed open by the change in pressure and the spider literally jumps like a spring being released.

Spiders also have a unique way of feeding. They are unable to eat solids since they lack chewing mouthparts, so instead, they inject their victim with digestive juices. When the tissues inside have been fully dissolved, the spider eats the contents like soup.

As for mating, male spiders mate with their mouths. Their pedipalps (feelers) are swollen and hollow with a corkscrew shape on the end. Each corkscrew shape is unique for each species to avoid mating with the wrong species.

Golden Orb Weavers (Nephila spp.) are commonly seen along the Skyrail cableway. The females are quite large when fully grown (hand span or larger) and their abdomen is long and narrow until fully pregnant with eggs. The males are tiny and vary in colour from orange to black. Several males are often spotted on the yellowish web and will fight for the right to mate with the female. The winner wraps his sperm in a small web and picks them up with his hollow mouthparts. The mouth parts have corkscrews on the ends which function as keys to the female's genitals. After mating, the male guards the female to stop other males from removing his sperm packages and replacing them with their own; they die shortly after. The web of these spiders is the strongest in the world.

Jewel Spiders (Gasteracantha spp.) are very common in the rainforest, but often overlooked despite their exquisite beauty. They have bodies the size of a 20 cent piece or smaller. The body is usually ornately coloured with intricate patterns on their backs. The webs are generally quite small and almost invisible. Apart from living in rainforests these beautiful spiders also live in local gardens and in the mangrove forest.

Giant Green Huntsman Spider (Typostola barbata) is the most commonly spotted spider along the Skyrail cableway. Apart from being quite large (hand span or larger) they are flat and have crab like legs. They have green blood that can be seen through the leg joints. Having a flat body allows them to hunt in narrow crevices and in ceilings. These large spiders don't make webs and rove freely. Although these spiders are intimidating to look at, the Giant Green Huntsman Spider is quite timid. Bites rarely harm humans, unless a severe allergy is involved.