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I GOT IT!
Have you read the manga Bio-Meat: Nectar? It takes place after a natural disaster has devestated Japan, and it's forced to develop a form of omnivorus (it eats anything that isn't glass or metal) lifeform, which is then sold cheaply (without the public knowing just what it is). In fact, it's THESE little monsters, designed to consume trash of all kinds, effectively killing two birds in one stone.
Problem is, they escape.
Second problem, they duplicate.
Third problem, they have a very wel developed sense of hearing.
If you haven't read it, DO!
Also, wiping EVERYTHING out just so that these fuckers can't eat it is a cause as good as any.