Over four decades, the Alien franchise has brought many different versions of the xenomorph creature to theaters.

: Some sci-fi aliens feel made up on the spot. Others seem so fully realized they could exist. This video explores the species with the deepest lore, logic, and worldbuilding in science fiction.

Introduction: Nonnative species in the world / David Pimentel -- The impacts of alien plants in Australia / Richard H. Groves -- Environmental and economic costs of invertebrate invasions in Australia ...

In these science fiction books, extraterrestrial beings are sympathetic, horrifying and everything in between.