It is paradoxical that the largest group of living things on the planet is the least noticed! Despite their numbers, many invertebrates remain largely invisible to us because they are too small to be seen, live under water or in the soil, or are otherwise camouflaged or partially hidden where they live.
The invertebrates are those animals which do not have a backbone or spine. This group includes many types of animals including:
In Australia, 86,000 species of insects have already been described. There are almost 2,000 species of spiders in 70 families. Described segmented earthworms number 325 species at present but it is estimated that there could be as many as 1,000 species nationwide. Even the ancient and unique velvet worms (which are neither worm nor centipede) number more than 40 species in Australia and all of these are restricted to moist environments.
Invertebrates such as worms and slugs have a very important role to play in ecosystems. Like the humble mushroom, these animals help break down organic matter and release nutrients which can then be used by other plants and animals.
Some invertebrates may also be important environmental indicators. We already credit amphibians as being our 'canaries in the coal mine' but a decline of, say, land snails or aquatic insects could also be a early warning sign that something is wrong in the environment. However, these invertebrates aren't as showy or endearing as a frog so we often don't notice when they disappear or suffer population declines.
You can read all about the invertebrates here and the specific sections on insects, butterflies and spiders.