Sticky Webbing is a Turf that cannot be dug up, though it was once possible. It's a white, creep-like substance that "flows" out of Spider Dens and Spilagmites and slows the walking speed of all creatures (except Spiders and Webber). If the Spider Den or Spilagmite is destroyed, the webbing will quickly disappear.
Sticky Webbing can also be found in Sacred and Labyrinth biomes in the Ruins. The webbing found there has no associated Spider Den or Spilagmites, as it houses Dangling Depth Dwellers, which reside on the ceiling above. This webbing cannot be removed.
Stepping on the Sticky Webbing (except as Webber) will cause Spiders to emerge and investigate the cause. The Spiders will only go near the edge of the webbing, and if they see no threat, they will return to their Den. However, Dangling Depth Dwellers will stay on the ground forever.