What the achievement asks
Complete a Nerubian delve on tier 8 or higher without spawning ambushers from Nerubian Webs and without taking damage from Nerubian Eggs. Ten points.
Brann can fail it for you
This is the thing that makes Spider Senses different from the other two delve challenges. If Brann walks into a web, the achievement fails, and he moves constantly during a fight.
The tell is his own voice line. If you hear him say that the webs will summon nerubians and not to stand in them, it is already over: leave and start again rather than finishing the run.
Nothing you do controls where Brann stands, which is why this one takes more attempts than it should. Track the achievement while you run so you can see the moment it turns red, and treat a failure as a two-minute loss rather than a thirty-minute one.
The Underkeep does not count
The Underkeep is treated as a nerubian delve everywhere else in the game and does not count for this achievement. Running it is a wasted evening.
Pick the delve by how much web is on the floor
The amount of web underfoot varies enormously between delves and between stories, and that is the whole difficulty.
Fiery Grounds is the story to wait for. It hands you a flamethrower, and burning the webs away removes the mechanic entirely. Players report getting this on the first attempt when that story is up.
Avoid Earthcrawl Mines. Its mobs throw fresh webs directly under your feet during combat, which means you can play perfectly and still fail to something you could not have avoided.
The Dread Pit is the calmer option. On days when the story does not involve freeing people from webbing, there is very little web on the floor at all.
Before you kill the last boss
Check that the achievement is still tracking green. Several players have finished a flawless run only to find it had failed much earlier, and the ones who caught it early lost minutes instead of a whole clear.
Where it fits
One of the pieces of Glory of the War Within Delver, which rewards the Ivory Goliathus mount and is part of Worldsoul-Searching, the War Within meta.