Can bumble bees feel something like happiness? It might seem unlikely, yet honey bees exhibit pessimism and crayfish can experience anxiety. To find out whether bumble bees have something akin to positive emotions, scientists trained 24 of the insects to enter a closed chamber via a metal cylinder. Inside, they faced a wall with four tubes. One was marked with either a blue or green tag. The bees learned that if they entered the green-tagged tube, they would get no reward—only water. But the blue-tagged tube led to a 30% sugar solution. They were then given an ambiguous test, where the tube wasn’t clearly marked blue or green. In this test, as the bees entered the metal cylinder leading to the chamber, half received a droplet of a 60% sugar solution; the other half did not receive a reward. The sugar-treated bees took less time to decide to enter the ambiguously marked tube, suggesting that the sweet treat had led them to be optimistic about what they would find, the researchers report today in Science . Eating sweet food makes people happy, they note. And that feeling leads us to make optimistic choices in ambiguous situations, such as gambling—just like the bees. Other experiments showed that the insects weren’t merely more excited or active because of the sugar hit; instead, the treat induced a positive feeling that affected their behavior in other situations. For instance, the sugared-up bees returned to foraging faster after being momentarily caught and lightly squeezed in a trap that simulated a predatory crab spider’s attack than did the control bees. The scientists also ended the bees’ optimistic behaviors by giving them a dopamine inhibitor, which blocks the brain’s reward center. Optimism is part of human emotions, and finding it in bees makes the scientists themselves optimistic that the feeling has a long evolutionary history and is likely found in many animals.