From the film The Dark Crystal, The Garthim are under control of the SkekUng. The garthim were large crustaceous golem-like ceatures that followed SkekSès ever comand. The garthim were created by SkekTek the scientist the scencetist skeski and lived in caverns beneath the Castle of the Crystal. The Garthim were created and used to ravage Thra and returned with kidnapped Gelfings or Podlings for the Skeksis to enslave and drain their essence.
Two garthim laying in wait
the garthim resemble a mix between a beetle and a robot and do not appear to be in control of their own lives acting almoast as an zobie army near the end of The Dark Crystal, fall apart like broken pootery or glass, revealing nothing within, but a dusty outer shell. its probale they all died at the destruction of the castle.