Webs can be left floating in mid-air for a variety of reasons, such as getting caught in a tree and the tree subsequently being chopped down (Bug 595). This tool finds the floating webs and makes them fall to the ground.
See clear-webs if you want to remove webs entirely.
Make webs that are floating in mid-air drop to the ground
Make webs that are above the ground for any reason (including being stuck in tree branches) fall to the ground.