Daintree Rainforest - Wet Tropics Spiders

(Photo: WTMA)

Australia leads the world in its number of resident venomous spiders as well as the strength of their toxicity. However, of almost 9,800 species (about 2,500 species have been named)of spiders in 70 families throughout the country, most are perfectly harmless and interesting.

As with other animal types, spider diversity in the Wet Tropics is broad and many fascinating species occur here that range from the ominously large to the tiny and hardly noticed, and from the dullest browns or black to the vibrantly hued or deceptively shaped.

Spiders are classified according the strategies they use for feeding. Spiders which appeared earlier in the evolutionary scale feed by waiting in a burrow for food to come along before grabbing it. Following them are spiders which actively wander looking for food and which catch it by ambush or chasing it down. The evolution of flying insects created a need for spiders to evolve new ways of catching food which couldn't be chased and so the earliest web weavers arose.

A few facts about spiders:
- Most spiders feed on insects and other arthropods but when it comes to the Bird-eating Spider (see the Primitive spiders page), there is some speculation about larger prey being consumed such as warm blooded animals and frogs.
- Spiders cannot eat solid food - they suck out their victim's body fluids and softer tissues using powerful stomach muscle contractions.
- A spider periodically sheds its skin (exoskeleton) so that it can grow (called moulting). - Immature stages in between moults are called instars (same as for insects). Each species has a particular number of instars that it will go through before reaching its final adult stage.
- The silken material used to create webs or wrap up caught prey is made mostly of proteins and amino acids. There are actually seven different types of spider silk created for specific uses (such as web construction, anchor lines, wrapping prey, lining nests, etc.) and most spiders posess at least three types of spinnerets (the extensions at the end of their abdomen which exude the sticky threads).
- Once male spiders have mated, they no longer have any interest in eating and die shortly after. But even in death, they often serve a purpose. After the females have mated, they need to build up their energy for egg laying and protecting the egg case. Therefore, the females of many spider species simply make use of the males by eating them after mating!

Allowing spiders to take up residence around dwellings can be beneficial in that they catch other annoying insects such as mosquitos and flies. If you find a spider in your home that you don't want there, you can use a large drinking glass to trap it by gently placing the open glass over the spider as it sits on a wall or flat surface; slide a sheet of paper under the rim so that the spider is trapped inside when you move the glass. Take it outside and toss it into a shrub or let it escape onto a tree trunk. Avoid using insecticides to kill spiders as these chemicals also kill other animals like frogs.

Rest assured that while you might see some large spiders and perhaps even some venomous ones, none will behave like the dangerous villains in the horror film Arachnophobia! A good 'rule of thumb' regardless is to look and admire but don't touch any spider you find. Even those without venom could still have a nasty bite.

Information cortesy of the Wet Tropics Management Authority.