FactSentinel

Spiders are not insects. They belong to a separate class of animals called Arachnida, which also includes scorpions, ticks, mites, and harvestmen. Insects belong to the class Insecta. Both groups are part of the larger phylum Arthropoda, which covers animals with jointed legs and external skeletons, and this shared ancestry is why the two are so often confused. Being related at the phylum level does not make one the same as the other, much as a lizard and a mammal are both vertebrates without being the same kind of animal.

The anatomical differences are clear and consistent. Insects have three main body segments (head, thorax, and abdomen), six legs, and usually one pair of antennae. Many also have wings. Spiders have only two main body segments, the cephalothorax and the abdomen, and they have eight legs. They have no antennae and no wings. Instead of antennae, spiders use sensory hairs and a pair of leg-like pedipalps to detect their surroundings. Spiders also have fangs (chelicerae) rather than the chewing or sucking mouthparts typical of insects, and most species have eight simple eyes rather than the compound eyes common in insects.

The misconception persists largely because spiders are small, crawl on the ground, and are often grouped with insects in everyday language as "bugs." Pest control products and general descriptions of "creepy crawlies" reinforce the confusion. Biologists universally classify spiders as arachnids, and this distinction is standard in zoology textbooks and taxonomic references worldwide.