arachnids

Arachnids are arthropods in the class Arachnida. They have four pairs of legs (eight in total), two main body regions—the cephalothorax and abdomen—and lack antennae and wings. They typically possess chelicerae for feeding and venom delivery, and pedipalps for handling prey and sensing. Most have simple eyes. Gas exchange is through book lungs or tracheae, and they have an open circulatory system. Excretion is largely via Malpighian tubules. Silk glands, when present, produce silk from spinnerets.

The arachnid lineage includes spiders (Araneae), scorpions (Scorpiones), mites and ticks (Acari), and harvestmen (Opiliones). Spiders produce silk and many spin webs, though some are free-roaming hunters; silk is used for webs, egg sacs, and safety lines. Ticks and mites feed on animals, plants, or detritus, with some species acting as parasites or disease vectors. Scorpions have a segmented tail ending in a venomous sting and a pair of pincers.

Ecology and life history: They are mainly carnivorous, preying on insects and other small animals. They inhabit diverse environments, from forests and deserts to caves and human dwellings. Reproduction is typically sexual; many species perform courtship and care for eggs or young. Juveniles hatch as miniature adults and grow through molts rather than undergoing complete metamorphosis.

Impact and diversity: Arachnids play key roles as predators of pests and, in some cases, as disease vectors. They are widely studied in biology and ecology, and there is extensive taxonomic diversity with tens of thousands described species and many more likely undescribed.