After the Saint Basil's Cathedral in Moscow turned into a monster the world realized our weapons were not enough, so governments all over the world came together and started the SOS program. We built monsters of our own. We constructed giant human shaped robots and our most famous one, the Wasp. At first they were fails. The Wasp's tail would rust the Wasp itself dropping the pilot thousands of feet. It took the world a while but finally the SOS program got it right.
The Wasp was a giant metal wasp piloted by a single human. The Wasp's mouth was a very wicked drill that could tear any metal to shreds. Its stinger was what we called the rust spike. When the stinger stabbed into a building it would inject nano bytes that would both rust and dissolve the metal in a matter of seconds, which enabled us to destroy the monsters in a matter of minutes.
With this we were able to fight back and destroy the monsters.