Well Cliff just said via twitter "For the LAST Time the locust queen is not Marcus's mother. That would be STUPID!"
Anyway i felt with that outta the way i could suggest my theory, and not have people say no, the queen is marcus's mother.
My theory. Its the Predulm Wars. 20 years in. The Cogs are losing. And losing bad. they need something to turn the tides in the war. Adam Fenix is given a project. Create Super Soldiers that could defeat the opposition. During his creation, something goes horribley wrong and they turn out to be mutant creatures that want to kill ALL humans not just opposion. Fearing for everyone, Adam realises there is only one thing to do. Bury these creatures underground where they cant hurt anyone but themselves.
Underground for 50 years, they have plenty of time to reproduce enough to create that many locusts. Oh and the Locust Queen. She was Adams closest attempt at a human super soldier, which is why she speaks highly of him.