When the Wildlife Raid is active the Unstable Tunnels will summon a combination 1-4 Drillworms and/or Drillworm, Glooth Anemones Anemones, or Behemoths around them. Typically the summons will just stand still until you damage them I've noticed while hunting there.
Source: https://tibia.fandom.com/wiki/Unstable_Tunnel