Glow Spiders

Found throughout cave systems all across Orliüm, the glow spiders offer natural luminescence from a glowing bulb on their abdomen. At full size, they are perhaps as large of one's fist. The digestion process of a glow spider produces light in that bulb as a chemical reaction. The resulting light lasts several hours. Feeding them fireflies from the surface makes the illumination brighter, but this effect is short lived. Their effective light radius is about half that of the average torch if well fed. Unlike other spiders, glow spiders do not capture their food in webs. Their faint glow attracts certain insects which they eat. A glow spider can regulate its luminescence by spreading out its hairs.
Underdwellers found that glow spiders could be trained for use as flameless sources of light. By keeping a pouch of food strapped to their chest, the spider will cling to the front of their clothes and feed. These "clingers" served as a means of always keeping the light aimed ahead of the person. While this was practical enough in more populated cave systems, where bioluminescent fungi and other plants were plentiful, clingers proved less effective outside of well traveled caves. They proved to not provide enough light to navigate by, which demanded more advanced training techniques.
Developed later on, the "tap dance" method was introduced that allowed the spider to travel independently but remain in sight. Since glow spiders respond to vibrations and sounds, a trainer places the spider on the ground.  The person then taps their foot and runs a finger along the spider's back in a given direction and tosses food ahead. The spider then moves forward to eat. After about ten paces, the trainer repeats the process. Eventually, the spider learns to preemptively "lead" their trainer ahead, expecting food when the trainer catches up. As the spider learns, the trainer starts dropping food after longer distances, and feeling of feet approaching encourages the spider to keep moving forward, maintaining that distance away until recalled by another distinct tapping of the foot.
Highly advanced trainers can coordinate many spiders together into a single swarm, with each spider taught to maintain a particular distance and direction. The trainer walks in the center of the swarm, with some "leader" and some "follower" spiders, providing light in all directions and in a wider radius. A "return" foot tap would recall the entire swarm to the trainer. This is effective when a group of people wish to travel together.