III.

Behavior and Importance

Arachnids are usually predaceous. Often they hunt or lie in wait for small animals such as insects. Food may be partly or wholly broken down by secreted fluids and then sucked in. Arachnids have simple eyes and various prey-subduing structures, such as the segmented, stinging tail of scorpions and the abdominal spinnerets with which spiders construct elaborate insect traps (orbs or webs). Mites constitute the largest and most diverse order of arachnids, followed by the spiders. Some mites feed on plants and a few species are serious agricultural pests. Some are predaceous, often feeding on other species of mites. Parasitic lifestyles are common among mites and many are of veterinary and medical importance. Ticks are a distinct bloodsucking subgroup of mites specialized for parasitizing reptiles, birds, and mammals. Ticks carry organisms that cause serious human diseases, such as Lyme Disease.

The bites of some spiders and the stings of a few species of scorpions are dangerously poisonous to humans (see Black Widow Spider, Brown Recluse Spider). However, most arachnids are harmless and contribute to the balance of nature by controlling the populations of the insects they prey on or the plants, reptiles, birds, or mammals that serve as their hosts.

Scientific classification: Arachnids constitute the class Arachnida, in the phylum Arthropoda. The class is divided into 11 orders: the Acari or Acarina (mites and ticks), Amblypygi (tailless whipscorpions), Araneae (spiders), Opiliones (daddy longlegs), Palpigradi (palpigrades), Pseudoscorpiones (false scorpions), Ricinulei (ricinuleids), Schizomida (micro whipscorpions), Scorpionida (true scorpions), Solpugida (windscorpions), and Uropygi (whipscorpions).