"If you tell them, you give them time to destroy evidence and think up a story, " he says.

WSJ: Business Owners Get Burned by Sticky Fingers

"They found out how you could make them destroy themselves, " the former official said.

WSJ: U.S. Team Behind Computer Worm That Hit Iran

When you destroy their nest and make them migrate to a new one, they manage it very efficiently, as you would expect.

BBC: NEWS | Science/Nature | Ants - learning from the collective

Once you've got them, you don't need to destroy any more embryos, but each time you get a new one of these embryonic stem-cell lines, you need to destroy an embryo.

NPR: Ethical Guidelines for Stem Cell Research Proposed