Introduction to arthropods
Spiders are not insects. A female wolf spider (Pardosa sp.) warms her egg sac in the sun.
Arthropods are animals that lack a backbone. Such animals are said to be invertebrates. The invertebrates includes animals such as snails (molluscs), crabs (crustaceans) and, of course, insects.
The arthropod body is supported by an hard, outer layer. This acts as an external skeleton - or exoskeleton. The body muscles are attached to the inside of this exoskeleton. It is made up of rings (called segments) which are attached to one another by flexible membranes. This allows movement of the body to take place. The name arthropod refers to their jointed limbs, which are their chief characteristic. (Arthros = joint, Podium = foot).
There are various types of arthropod and they are classified in to groups based on common features. With a little care they may be easily and quickly recognised in most situations:-