I love Ridley Scott's Alien (and Aliens for that matter. I pretend the rest of the series doesn't exist). The xenomorph itself is one the most fascinating of all movie monsters, but what I love about it, is that despite how alien it can seem, it's disturbing lifestyle is not alien at all. We have chestbursting xenomorphs here on earth, we just call them wasps. They (at least the parasitoidic variety) lead a lifestyle so horrific that they helped push Charles Darwin to agnosticism. "I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidæ with the express intention of their feeding within the living bodies of caterpillars..."
Wasps are not alone, during my biology undergraduate education I learned that the harshness of natural selection is not limited to predation. Parenting can be just as brutal as any hunt. Sibling competes against siblings, parents and offspring have divergent strategies on breastfeeding, and mothers may devour their offspring when conditions are bad. Where am I going with this? Well I just published a new flash fiction piece. So read it if you get a chance, and thank your mother the next time you get the chance, for not devouring you when the house flooded in order to regain her investment of calories.