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All about Bugs

Great green bush-cricket

(c) Steven Falk

Invertebrates are animals without backbones and make up the great majority of animal life, with 40,000 species in Britain alone and many millions on Earth.

What is an invertebrate?

From Shetland to Lands End, from the Arctic to the Tropics, from the depths of the oceans to the tops of mountains, the majority of animals are invertebrates.

  • To most people, an animal is a mammal, bird, reptile, amphibian or fish. These are all vertebrates, since they have a spine made up of vertebrae.
  • But invertebrates are also animals. Like vertebrates, they, generally have a heart, nervous system, senses and mobility. What's different is that they lack a spine.
  • The variety of invertebrates is staggering, and they provide some fabulous examples of evolution and specialisation.
  • In many cases they are able to transform themselves from one thing into something completely different during their life cycle.
  • Once a mouse, always a mouse. Yet a caterpillar that can only crawl and eat foliage is able to completely transform itself in a pupa to become a beautiful, flying, nectar-feeding butterfly – two completely different looking animals within the lifecycle of one species. And for all the skills of a bird in making a nest, an orb web spider surely rivals the finest engineer in its mastery of structural design.

All you have to do is look… to see that the miniature world of invertebrates is full of beauty, amazing abilities and extraordinary events and activities.

Are invertebrates always insects?

The majority of Britain's invertebrates are insects. We have about 27,000 species of insect. The largest examples include the Stag beetle, Death head hawkmoth and queen Hornet. The smallest include tiny wasps and springtails less than 1mm long.

But even the tiniest insects can be extraordinarily beautiful when examined close-up and often have fascinating lifecycles.

Our insects include beetles, flies, bees, wasps and ants, true bugs, butterflies and moths, mayflies, dragonflies and grasshoppers: in fact about 25 major groups (Orders). Related to insects are other types of invertebrates that also have jointed limbs and an external ‘exoskeleton’, such as spiders, crayfish, water fleas, woodlice and millipedes. Together with insects these are known as Arthropods, and we have well over 3,000 species of arthropod in Britain that are not insects.

Additionally there are many other invertebrates that are not arthropods with totally different types of bodies, such as snails, worms and sponges. This includes over 3,000 species belonging to at least 13 major groups just on land and in freshwater habitats, plus many further species and groups in the sea.

If there are so many kinds, does it matter if some become extinct?

  • All species have a special place in the web of life, a web that helps to supports humans too.
  • This complex web has taken millions of years to evolve. Each species within it matters, and cannot be replaced once lost.
  • Many types of invertebrate may yet be recognised as having a benefit to man, in pest control, pollination of crops or by providing special chemicals for medicine.
  • Almost all of them have incredible lifecycles and stories yet to be told. We still only know a fraction of what there is to learn about invertebrates. Some may even go extinct before we discover them.
  • When we talk about biodiversity, we should think of it as all plant and animal life, including all the invertebrates, and understand that, just like a spider’s beautiful and delicate web, the web of life only works properly if every tiny section of it holds firm.
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