Tarantulas do not, unlike most other spiders, spin complicated webs in order to catch their prey. Tarantulas do, however, create the silk that spiders use to spin webs, but for different reasons. Tarantulas use silk for defensive purposes and to adhere to surfaces.
Although tarantulas do not catch their prey in webs, they do use their silk when constructing a shelter. For example, tarantulas will often cover the inside of their dwelling with silk in order to stop insects from trying to invade their nests. In this case tarantulas cover the dirty ground inside of their nests with the silk, similar to how we humans lay carpet in our homes.
What is most interesting, however, is the recent finding that revealed that tarantulas do indeed use silk in order to stick to questionable surfaces, but they do not get that silk from their spinnerets. For years scientists have not known where exactly tarantulas are getting their silk from when they need to stick for a vertical crawl. Some scientists insisted that they somehow grabbed the silk from their spinnerets (silk producing organs), whereas other scientists believed that tarantulas secrete the silk from their feet.
Well the case is now closed as a team of researchers used a complicated experimental setup to determine the source of their silk, and they discovered that the silk originated from their feet, and not their spinnerets. On the other hand, spinnerets were found for the very first time on the feet of the tarantulas that were being studied, so maybe they were both right. In any case, a lot of bets were won and lost in the scientific community recently.
What factors would make it difficult to determine all the places on a tarantula's body where silk could secrete?