The Mosquito pieces can be added to a standard Hive set before the start of the game giving each player 12 pieces to play with.
During the game, they are placed in the same way as the other pieces. Once in play, the Mosquito takes on the movement characteristics of any creature it touches at the time, thus changing its characteristics throughout the game.
A Mosquito itself has no movement characteristics, so it gives no movement characteristics to an adjacent Mosquito. Hence a Mosquito cannot move if it touches only a Mosquito.
Exception: If moved as a Beetle on top of the Hive, a Mosquito continues to move as a Beetle until it climbs down from the Hive.