From their website:
Diminutive sentient xeno-crustaceans native to Sepulveda 7, the Chewks live in giant underground drilltanks which travel deep under the sands of the central Sepulvedan deserts. When they sense an intruder or there is an opportunity to raid travelers in the desert, the huge drilltanks will broach and out from them will spill tribesmen to the attack. Alternately, the Chewks will meticulously set up ambushes amongst the sand dunes to snare unwary foes as they stagger across the desert.
The Chewk is very small, but a deadly adversary all the same, being brave, crafty, and armed with crude but powerful fusion weapons. Tribesman generally carry a single shot bolt-activated rifle which is loaded from the muzzle, a powerful chambered fusion round being capable of penetrating the toughest armour — a necessity on a planet where most creatures have thick shells. Heavier weapons are available as well, ranging from the chewkbomber (a mortar) to the chewkzooka (a chewk-portable rocket launcher) to the chewkgun, which has a larger round than the checkrifle and a fully automatic action.