Setae are single cells called trichogen, that grow through the exoskeleton of an arthropod and stiffen into a hollow flexible tube. The dendrite of a sensory nerve, may extend into this tube, or a gland may open into it to make a mechanical and chemical sensor to detect taste, touch, odor, temperature, vibration, or wind direction. Setae look like hairs but they’re not that simple. * If they don’t serve as sensors, they might be defensive, cloaking a bug, poisoning its predators, or making it easier to free itself from a web, or they may have useful mechanical properties, giving a bug the ability to walk on walls, land upside down, or skim the surface of a pond.