Somehow I missed this in 16 years of schooling...

      In 1493, his magnificent account of the great Columbian exchange that followed contact between the eastern and western hemispheres, Charles Mann show how again and again the forces that truly shaped history came from below, not above.  For instance, the American Revolution was won by the malaria parasite, which devastated General Charles Cornwallis's army in the Carolinas and on the Chesapeake, at least as much as it was won by George Washington. ...Referring to female mosquitoes of the species Anopheles quadrimaculatus, he writes:  "Those tiny amazons conducted covert biological warfare against the British army."...Most white colonists had survived malaria in their youth and acquired some resistance...So the American south was the worst possible place to invade with foreign troops....When it came time to fight a battle, most of the army was debilitated by fever, including Cornwallis himself...."Mosquitoes," says McNeill, "helped the Americans snatch victory from the jaws of stalemate and win the Revolutionary War, without which there would be no United States of America.  Remember that when they bite you next Fourth of July."

-Matt Ridley, as culled from The Evolution Of Everything