@mooseymcman: I don't believe it does, but it has been awhile since I've read it. It does explain that they're terraformers from another planet. They eat everything and shit/bleed nano-machines that make any area affected uninhabitable for any form of native life, thus the reason why the U.N soldiers powered-armors cover the entire body. The mimics were also damn near impossible to kill, due to their harder then hell armor. Which was why both Rita and Keiji Kiriya (the main character of the light-novel) used battle axes instead of a sword. Hell even the way the time/respawn mechanic is different (from what I've read). It should be noted that Kiriya starts out as a pure greenhorn he was just another guy who had been conscripted for the losing war. he arrived start out of boot-camp.
The author of the LN used videogames as his inspiration for the whole time/respawn mechanic and it was the reason why Kiriya was a complete greenhorn.
Sorry for the info dump, I got carried away.
I've covered up the small origin behind the mimics due to it being a possible spoiler.