Spider Walls are naturally-generating background walls found in Spider Caves. Unlike other naturally occurring walls, it can create Cobwebs over time, allowing it to be used to farm Silk. These walls can be destroyed with a hammer, but will drop nothing. These walls also do not stop enemies from spawning and cannot be used for proper housing.
Player placed cobweb may not be retrieved when destroyed.
Player-crafted Spider Walls do not spawn cobwebs or contribute to a Spider Cave biome.
On the background texture of the wall there seems to be a bound NPC. This could be a reference to the actual Lost Girl, or more likely the Stylist NPC as she will initially spawn (bound before rescue) within a Spider Cave.