This is one of those common misconceptions that sounds like it's actually true. Spiders are tiny and often dark creatures that crawl around on their little legs. Like wasps, crickets and caterpillars, spiders don't have spines. They also seem to share an innate ability to get inside homes, cars and other places where they aren't "supposed" to be.
There are a few physical aspects that set spiders and other members of the Arachnida group —like mites and ticks — apart from their insect friends. The Insecta group is characterized by three main body parts: the head, thorax and abdomen. Spiders, on the other hand, have only two main body parts: the cephalothorax — a combined head and thorax covered by a hard shell- and the abdomen. They lack an insect-like antennae and have one more set of legs than insects, which generally feature six limbs [source: Explorit Science Center].
Spiders also probably look better in a bathing suit. Their slender waists distinguish spiders from other arachnids [source: Explorit Science Center].