[Akuma]

Originally Posted by CoMaToSe

Okay I am confused about one thing. How did the ant lions, headcrabs, barnacles, and shit get on earth? The combine fight them as well as the humans, and the combine hav their own aliens they use, like the striders, the gunships, and those tanks and flyers you see for a second as youre being transported to Dr. Breen's lab near the end. So, how did those aliens they fight get on earth?

Portal storms.

http://fragfiles.org/~hlstory//timeline.htm