They are very common, and we have all seen them on numerous occasions - anything with 8 very long legs and a tiny body is likely to prove to be a harvestman on closer inspection. They are easy to distinguish from true spiders, because their body is a single lump, whereas a true spider has a two-piece body separated by a waist. Another feature of arachnid anatomy that most people fail to get is that all 8 legs of a true spider are attached to the front part of the body - the thorax, the part of the spider immediately behind the head. The abdomen - the rear end of the body, behind the waist - has no legs at all.

The three best known orders of the arachnids are the spiders, the scorpions and the mites-and-ticks (Acari). But there are, always depending upon the latest taxanomic considerations, about 8 further orders. We have just been talking about the harvestmen. Some other orders include solpugids (alias camel spiders), whip scorpions (alias vinegaroons), amblypygids (alias tail-less whip scorpions or whip spiders) and pseudoscorpions. We do have pseudoscorpions in Britain, though they are rare and hard to find; the others are all found only in warmer places.

Arachnids themselves belong to the subphylum (of the arthropods) called Chelicerata, but the only other extant member of that subphylum are the horseshoe crabs.