When a few species of stalk-eyed fly stopped roosting on hanging rootlets in Malaysian streams, two of the three arms race ingredients vanished; females stopped gathering in harems on hanging threads (they were no longer economically defensible), and fights stopped being duels. With two of the race-stimulating ingredients gone, the flies' arms races collapsed. They lost their extreme weapons.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 438