Invertebrates are the most successful and prolific animals on the planet. They have been around for over 400 million years and dominate the animal kingdom in terms of numbers of species and numbers of individuals. Invertebrates have also adapted to occupy practically every ecological niche. So really, when we talk about 'biodiversity' we are talking about invertebrates.
The majority of animals on earth are invertebrates
The vertebrates - mammals (such as ourselves), birds, reptiles, frogs and fish are only one group of thirty that make up the animal kingdom. Therefore all the vertebrates put together are only a tiny proportion of the species of animals on earth. All the rest, well over 90%, are invertebrates.
There are millions of invertebrates yet to be discovered
Even when we include plants, algae and micro-organisms, invertebrate animals are the dominant life on earth. The number of invertebrate species is staggering and new species are being discovered all the time. To date scientists have only documented 1.7 million invertebrate species but they estimate numbers could range from 5 - 30 million. At this rate it will take scientists over a thousand years to identify all invertebrate species. Unfortunately, species numbers are declining faster than we can record their existence.
Invertebrates are incredibly abundant
Estimates of invertebrate densities in localised areas have found invertebrates are so abundant that it is difficult to even approximate global numbers let alone count them. For example, an area the size of an Olympic swimming pool in a rainforest may contain three million insects. Termites alone can reach abundances of up to 10,000 individuals per metre squared.