There is a war going on between a certain tropical butterfly, Heliconius sara, and its only food source, the passion vine. This war involves chemical warfare. More precisely, the plant arms itself with cyanide bombs that are rather useful in getting rid of most insect pests.
Over the past few decades, the earthworm population has severely decreased. Since the New Zealand flatworm accidentally made its way to the British Isles in 1963, it has wreaked havoc on some of the land, devouring fields of earthworms.