Until now, only mammals have been shown to seek out addictive drugs in the absence of a concurrent natural reward such as sugar. Brian Entler, Timothy Cannon and Marc Seid at the University of Scranton in Pennsylvania provided the ant Camponotus floridanus (pictured) with sugar water laced with the drug, then, over the course of several days, reduced the sugar concentration to zero while increasing the morphine level. The team then gave the ants a choice between sugar water and a sugar-free morphine solution. Of the ants exposed to morphine, 65% preferred the drug — roughly twice the rate seen in unexposed animals. The brains of morphine-trained ants also showed elevated levels of dopamine, a neurotransmitter associated with reward.