Quoted from an article by Amina Khan in the Saturday, 9/10/2011 edition of the Los Angeles Times. Just so you know, it's pretty disgusting, and possibly nightmare-inducing.
Scientists have isolated a viral gene that induces zombie-like behavior -- in caterpillars. The virus causes gypsy moth caterpillars to climb to the tops of trees, where they die and their disintegrating bodies rain infectious particles on their unsuspecting brethren below.
[...]
"You end up with this sack of virus that opens up," said...Kelli Hoover, an entomologist at Pennsylvania State University. "It melts and it's gooey and you get [a trillion] of them raining down and spreading down on the leaves. It's a very efficient virus."
Excuse me, I have to go and write a Torchwood, or maybe X-Files, fanfic now.