11 Most Terrifying Sci-Fi Movie Monsters
9. Xenomorph - Alien Series
The Alien franchise has stretched so long and with so many ups and downs that its titular creature might be considered somewhat passe, but it's easy to forget how viscerally terrifying these things were when they first burst (pun intended) onto cinema screens in 1979.
Initially of unknown origin (until Prometheus and Alien: Covenant came along, much to dismay of many), these xenomorphs were first discovered by the crew of the Nostromo in an ancient derelict spacecraft filled with massive, pulsating eggs and signs of turmoil.
The xenomorphs start life as "Facehuggers" that force themselves onto the faces of unwitting victims, planting an egg down their throat. Said egg eventually gestates into a "Chestburster" which violently explodes out of the host's chest. In a matter of hours, the Chestbursters grow into fully-formed Xenomorphs, taking on the characteristics of their initial hosts.
They're predatory, primal creatures with no greater purpose than propagation and self-preservation of their own species. Like insects, xenomorphs are eucsocial creatures, with a single Queen alien breeding castes with varying specialized traits.