Arachnid is a scientific term whose etymology leads directly into one of the most compelling myths in the Greek canon—the story of Arachne, a mortal weaver whose skill rivaled that of the gods and whose punishment gave spiders their name.
The Greek word arakhnē means both spider and the web a spider produces. It is also the name of the mythological figure whose story is most memorably told in Ovid's Metamorphoses (8 CE). According to Ovid, Arachne was a young Lydian woman of humble birth whose skill at weaving was so extraordinary that nymphs came from far and wide to watch her work. She boasted that her talent exceeded even that of Athena (Minerva in Roman tradition
Athena, disguised as an old woman, warned Arachne to show humility, but Arachne refused. The goddess revealed herself and accepted the challenge. Both wove magnificent tapestries: Athena depicted the gods in their glory and the punishments of mortals who defied them, while Arachne wove scenes of the gods' crimes—their rapes, deceptions, and abuses of power. Arachne's work was flawless.
Enraged by both the quality and the content of Arachne's tapestry, Athena destroyed it and struck the weaver. Arachne, in despair, hanged herself. Athena, perhaps feeling a pang of guilt, transformed her into a spider—condemned to weave forever but never to create art. The myth is a story about the relationship between art and power, about the cost of truth-telling
The scientific application of the name came in 1801, when the French naturalist Jean-Baptiste Lamarck coined the class name Arachnida for the group of arthropods including spiders, scorpions, harvestmen, ticks, and mites. The class is defined by several characteristics that distinguish its members from insects: eight legs (rather than six), no antennae, no wings, and a body divided into two segments (cephalothorax and abdomen) rather than three (head, thorax, and abdomen).
The class Arachnida is enormously diverse, containing over 100,000 described species. Spiders (order Araneae) are the most familiar, but scorpions (Scorpiones), ticks and mites (Acari), harvestmen (Opiliones), and several smaller orders are also arachnids. The group has an ancient evolutionary history—scorpion fossils date back over 430 million years, making them among the oldest known terrestrial arthropods.
The word arachnid entered common English in the early 19th century, initially in scientific and educational contexts. It has since become the standard general term for the eight-legged arthropods, used in both technical and popular writing. The adjective arachnoid (resembling a spider or web) has found medical application in the arachnoid membrane, one of the three meninges surrounding the brain, named for its web-like appearance.
Arachnophobia—the fear of spiders—is one of the most common specific phobias in humans. The word combines arakhnē with Greek phobos (fear), and its prevalence has been debated by evolutionary psychologists, who argue about whether the fear is innate or learned.
The relationship between Greek arakhnē and Latin aranea (spider, also the source of Spanish araña and Italian ragno through rearrangement) is uncertain. They may derive from a common Mediterranean source, or one may be borrowed from the other. Either way, the spider has carried some form of this ancient name across the Indo-European world for millennia.