Pest Control

Pest Control an achievement in Baldur's Gate 3. It requires the player to kill the  Phase Spider Matriarch before her eggs hatch.

The matriarch and a number of other phase spiders are found in the Whispering Depths in Act One, which can be accessed from the Blighted Village, either by going down the well in the village's center, or by breaking a wall in the cellar of the blacksmith's workshop.

Strategy

To get the achievement, the player must kill the spider before she can hatch any of the three clusters of eggs located atop three stone platforms around her nesting spot. This is made challenging by the fact that her first action upon entering combat is often to use  Ethereal Jaunt to teleport near one of the egg clusters and hatch it.

The easiest approach is to have a party member with good stealth capabilities sneak onto the two platforms that are furthest from the matriarch, and destroy those clusters first. This is possible without it being noticed at all. Attacking the last egg cluster, which is closer to adult spiders in the area, is likely to be noticed and thus initiate combat, but this is not a problem since the cluster is easily destroyed in one attack.