20 Things You Didn't Know About The Xenomorph
8. The Enemy Of My Enemy
According to the in-universe manual Aliens: Theory of Alien Propagation by Dr. Waidslaw Orana, the Xenomorph might be the biggest threat to the expansion of mankind throughout the cosmos, but even they aren't exempt from the food chain.
Waidslaw explains that on the hive world of G-435 there is another creature that helps keep the Xenomorph numbers under control, by hunting and killing them. Although the creature is never given a name, it is described as a giant, lizard-like beast that is impervious to its foes acidic blood, giving them the edge in battle.