Web Sacs are Resource Nodes found commonly in spider-infested areas such as the Hedge or Spider Caves. They offer creature parts when broken, some of which are extremely valuable. To counter this, the sacs have a chance to spawn 0-4 Spiderlings when broken, and will attract the attention of all spiders nearby to investigate it when broken. Some spawn areas of the sacs are also created by Orb Weavers while others naturally spawn like other nodes.
They have a variant exclusive to Black Widows.