Bē (ベエ) are large flies (or possibly butterflies) found in Super Mario Land 2: 6 Golden Coins and Wario Land: Super Mario Land 3. In both of these games, Bē are rather rare and can technically deal no damage, since they run away from Mario as he approaches.
Bē first appeared in Super Mario Land 2: 6 Golden Coins, where they could be found in one Tree Zone level and two Macro Zone stages. These black flies typically remain in one place when undisturbed, but they, upon Mario's approaching, will quickly fly off in a diagonal manner (much like the flies of the Real World). Their runaway flight is just as fast as Mario's top running speed, making a Fire Flower almost completely necessary to defeat them.
Bē reappeared in Wario Land: Super Mario Land 3. Here they were found in the first three stages of the SS Tea Cup. In this game, Bē's actions were for the most part the same. They were also given an animation when idle and flew away in a more realistic, curved style. They would not move if Wario would crouch, which makes it possible for Wario to jump on them. If Wario manages to jump on one, a 10 Gold Coin would appear.