Spiders, Harvestmen and other Arachnids

The class Arachnida includes many orders, the best known being Spiders (Araneae) and Harvestmen (Opiliones). Other orders include Mites, Ticks and Pseudo-scorpions. Most, other than Mites, have 4 pairs of legs, and they are also different to insects in that they do not have wings or antennae.


There are about 670 species of spider in the UK, varying greatly in size from large ones such as the House Spider (often seen in our houses in the autumn) to the tiny ‘Money Spiders’.

They have 8 legs, ‘fangs’ with which to inject venom, and spinnerets to produce silk for their webs. They usually have 6 or 8 eyes.


Harvestmen / Harvest Spiders belong to the order Opiliones. They are often assumed to be spiders, but, unlike spiders, their bodies consist of only a single part, rather than the separate cephalothorax and abdomen that spiders have. Unlike spiders, they have only 2 eyes. They do not produce silk, and therefore do not make webs.

Gall Mites

Gall Mites belong to the Eriophyidae family, of which there are over 200 genera worldwide, with about 3,600 species having been described – though it is thought this might be less than 10% of the species that exist.

They are no more than 0.5mm long, and are rarely seen, but they are parasitic on plants and leave easily-seen galls, a response by the plant to the gall mite attack. The main means of dispersal is by wind.

They have 2 pairs of legs.