Poison the spider nests. is a Phase Beast Challenge encountered in Temple Steppes. Killing four Nethermancers initially standing in a circle around a cauldron triggers the opening of seven Spider Nests, releasing hordes of Nest Spiders.
To poison a nest, obtain a (delicious) Bottle of Poison from the cauldron and bring it to the nest.
After the seventh Spider Nest has been poisoned, three Nestmothers crawl from their lair mouths, located at the top of the map. Defeat them and collect the reward: scattered gold and one Golden Chest.
* monster level reflects the fact that the image is from an NG+ playthrough