We survey spiders from 43 families, 62 genera, and three arachnid outgroups for the presence and diversity of elongated pedicillate setae (EPS)—a complex system of probably sensory setae hitherto undocumented outside Theridiidae. Although not present in all spiders, these setae are sufficiently widespread to suggest they are primitively present in the order. Because they are absent in related arachnids, they appear to be a synapomorphy of spiders. Based on the morphology and orientation of these setae, it has been suggested that they supplement abdominal slit sensilla in proprioception, documenting the position and movement of the abdomen relative to the cephalothorax. Although still poorly known, the presence and distribution of these setae are informative at lower and higher phylogenetic levels.