Ants, like people and rats, can become addicted to morphine.

Scientists divided 90 ants into three groups. The first received a solution containing morphine and sugar, which was gradually reduced until the ants were receiving pure morphine.

The second group of ants got a sugar solution gradually reduced to pure water, and the third ate just sugar. Then the researchers offered all three groups the choice of sugar or morphine.

The ants that had been gradually deprived of sugar and those never exposed to morphine went right back to sugar. But about two-thirds of the ants given morphine chose it over sugar.

Ants are the first nonmammal to display drug-seeking behavior, the researchers said.