The animal kingdom is informally divided into two groups, the vertebrates and invertebrates. Invertebrates are a group of animals that have no backbone, unlike animals such as reptiles, amphibians, fish, birds and mammals who all have a backbone. Insects are invertebrates and make up the predominant life form on earth. There are estimated to be over 1 million different species. Insects undoubtedly owe their predominance to the development of wings which gave them a distinct advantage over the other invertebrates who could only spread by phoresy (hitching a lift) or in the transportation of goods, and their adaptability. Not all insects have wings of course, but those without, such as parasitic insects (fleas and bed bugs) have developed the ability to survive long periods without feeding, should they find themselves without a host.
When we talk about insects we usually mean any kind of bug or creepy crawlie but not all creepy crawlies are insects. Some fall into the official category of arachnids, crustacea and myriapods. Insects, like all living organisms, are classified so they are easier to name, talk about and manage. They belong to the 'Animal Kingdom' and are 'Arthropoda' which means they belong to the group of animals which have a chitinous exoskeleton (outside the body), segmented body and jointed limbs. Arthropods are thereafter divided into 4 classes:
- Insects. The largest group characterised by having a head, thorax and abdomen, a single pair of antennae, six legs and usually one or two pairs of wings.
- Arachnida. The group characterised by having a body divided into two parts, the cephalothorax and the abdomen, eight legs and no antennae. This class includes spiders, mites, ticks, and scorpions.
- Crustacea. Mostly water dwelling animals such as crabs, lobsters, shrimps and barnacles, but the ill-tolerated woodlouse is a land-living crustacean. They have two pairs of antennae and at least five pairs of legs.
- Myriapoda. Literally means many legs and includes centipedes and millipedes.
Insects commonly found in and around the home.