Known spawn locations (click for map image -- PH "a lurking ursarachnid") for your "ethernere.txt" map file (note for all known Ethernere Tainted West Karana named spawn locations, see this quest entry):
Grawrarawr's "Webspray" AE is a rear-directional AE, so can be avoided at its sides or its front.
It spawns egg sacks (not known if health-based or timed-based). These, if not killed within a certain amount of time, trigger the spawn of 3x "a tiny spider". They don't hit too hard and have low hitpoints, but they are immune to mez and their damage can add up if you have too many of them alive.