[Anaraxes]

Some researchers in Texas are trying an unusual approach to combat fire ants — parasitic flies that turn the pesky insects into zombies whose heads fall off.

http://www.chron.com/disp/story.mpl/...s/6420449.html

Then just add a little Science Gone Wrong, and you get Giant Radioactive Headless Zombie Fire Ants. Unless, that is, the flies mutate to become parasites of human hosts. Let the plague begin.