Tripwire:
Unlike many spider species, tarantulas do not use webs to catch their prey. They do, however, spin silk. If a tarantula lives in a place with dry soil, it will burrow into the ground and line the walls of the hole with silk to help keep sand and dirt out. If a tarantula does not burrow, it might spin a burrow out of silk, or live under a log or rock. Sometimes, tarantulas spin a line of silk near the entrance to a burrow, which, reports National Geographic, acts as a trip wire, alerting the spider to prey that is nearing its home. https://www.livescience.com/39963-tarantula.html