While AVP2 upped the bar in approximating the Aliens experience, the main emotion felt was the same exaggerated musophobia.    From Wordnik.com.  [Dailygame] Reference

The aliens in the Doom mods scared you the way a rat that crawls across the floor would scare someone with an extreme case of musophobia.    From Wordnik.com.  [Dailygame] Reference

In each case, I leave it to the reader to supply the words "fear of." acarophobia mites, parasites entonophobia ticks aelurophobia cats galeophobia sharks apiophobia bees hippophobia horses arachnephobia spiders musophobia mice bacilliphobia bacilli myrmecophobia lice bacteriaphobia bacteria soleciphobia worms batrachophobia frogs, toads swinophobia swine cynophobia dogs taeniophobia tapeworms eisoptrophobia termites taurophobia bulls A much smaller cluster of fears is centered on the plant world.    From Wordnik.com.  [VERBATIM: The Language Quarterly Vol X No 1] Reference