A Spilagmite is a different kind of Spider Den found only in Caves. It spawns Cave Spiders and Spitters. Spiders will regularly spawn from a Spilagmite at a rate of 1 approximately every 4 minutes, unless something makes them spawn differently (e.g. something walks on the webbing or an earthquake occurs).
A Spilagmite may contain up to 2 or 3 Spiders. The maximum may vary between Spilagmites. If the number of Spiders drops below the maximum, an additional Spider will spawn inside the Spilagmite in approximately 2 minutes. If an Earthquake occurs, all spiders outside will return to their home provided that home remains existing.
Spiders spawned from a Spilagmite have a 33% chance to be a Spitter; the rest will be Cave Spiders. Unlike Spider Dens on the surface, the type of Spider spawned is always based on this probability and does not change due to circumstances (e.g., attacking the Spilagmite).
A Spilagmite can be destroyed by mining it with any Pickaxe or a Pick/Axe, causing it to disappear and drop 1 Silk and 2 Rocks, possibly with an additional Silk and Spider Gland. After two strikes, the Spilagmite loses its ability to spawn Spiders. Striking an active Spilagmite will spawn all remaining spiders still contained within.
Like surface Spider Dens, Spilagmites produce Sticky Webbing, which will alert the Cave Spiders and Spitters inside if a creature touches it. When the webbing is stepped on, two spiders will emerge simultaneously, provided at least two are inside the Spilagmite at the time. If any Spider is attacked within range of the Spilagmite, or the Spilagmite itself is attacked, all remaining Spiders in the Spilagmite will emerge to engage the threat.
If the spiders that emerged are not killed and lose interest in their foe, they will stay outside their Spilagmite and roam the area.
- Allowing a Clockwork Rook to collide with a Spilagmite sometimes crashes the game.
- The player can attempt to heal a Spilagmite with any healing item; however, a mined one will not return to its original state, despite how many healing items the player gives it.