The vapour spider has a translucent and glassy appearance, and a rather soft & fragile body. They only appear at night, and seem more prevalent with stronger moonlight, but this is perhaps only because they are more easily seen. They seem to have no natural predators.
Vapour spiders create webs that are even more ephemeral than the standard variety, yet somehow even more resilient. It is said that they spin their webs not out of silk, but instead of smoke, mist, and moonbeams. Even the pattern of the web resembles swirls of vapour or smoke rather than a typical spiderweb pattern. Yet, when you pass your hands through it, the web is not disturbed, and remains undamaged.
They have never been seen eating an insect, nor has anything ever been seen caught in their webs. Vapour spiders do not even bite in self-defence. Some loremasters believe that they do not exist entirely in this plane of existance, and instead form their webs of visible ether, catching tiny spirit-creatures invisible to the eye.