Brood Mother Szikalax
From RoR Wiki
This is the first boss you can encounter when you make your way down. It spawns as you get closer to the Big Box of Shinies.
This hero spider is an optional boss. It is not required to kill her to gain access to the last boss.
Brood Mother Szikalax is one of the bosses that can drop various Gunbad jewelry.
Tactic
Brood Mother Szikalax does not require any tactics.
The moment the spiders pops up from the earth it spawns a group of level 40 adds, which should be taunted by the tank.
The adds continuously spawn throughout the fight.