The scroll and spellbook of web allow you to fire a web projectile (which would work similarly to a venom projectile, probably also being in VENOM_CLASS) or beam in a direction. If it hits a wall, it creates a web on the last non-wall space; if it hits a monster it creates a web on the monster’s space and immediately entangles it. If it goes far enough without hitting anything, it creates a web at the end of its range.

Giant spiders should possibly also be able to shoot a web like this, and if so the player should be able to do it via #monster when polymorphed into one.