Jeff Liebermann wrote:
carpenter ants[...]got into the TV antenna amplifier.
Nothing was eaten, but they secreted some kind of acid,
that ate the copper traces.

http://google.com/search?q=ants+formic-acid

Some birds have even figured out that squashed ants are useful.
http://google.com/search?q=ants+crows+formic-acid
There has been speculation that they get a buzz off this.