Spiders, harvestmen, mites and ticks

Spiders, harvestmen, pseudo-scorpions, ticks and mites belong to a group of invertebrates called arachnids. One of the most evident differences between insects and arachnids is the number of legs: insects have six legs, arachnids have eight.

Spiders make up the majority of the group, with over 50,000 known species. Almost all spiders are predators, and in turn are eaten by lizards, slow-worms and by many birds and small mammals. Scotland is a special place for mountain spiders which live under the stones on our highest mountains and for a few species that live in our native pinewoods.

Harvestmen, which superficially resemble spiders, are also predators of other animals including slugs, snails, woodlice, millipedes, centipedes - and spiders. Among the creatures that eat harvestmen are some birds, common lizards, beetles, centipedes and hedgehogs. However, harvestmen are able to produce a secretion from glands on their body which evidently deters some potential predators such as blue tits and house sparrows.

The first spiders and harvestmen  that look just like those we see today are found as fossils as far back as the early Devonian period - more than 400 million years ago.  The dinosaurs arrived about 170 million years later.