Skeeters are common enemies that have appeared in several Mario games.
Super Mario 64 and Super Mario 64 DS
Skeeter made its debut in Super Mario 64 along with its remake, Super Mario 64 DS. It appears in Dire, Dire Docks and Wet-Dry World. In the areas it appears in, it would aimlessly skate across the water, without trying to hit Mario. However, if Mario drained the water in Wet-Dry World, the Skeeter would pursue him for taking them off the water.
Super Mario Sunshine
Skeeter reappears in Super Mario Sunshine, but this time they're referred to as "Pondskaters". They only appear in Bianco Hills, where the skate across the water freely. But, when they spot Mario, they'll try to run into him. If Mario sprayed them with water, they would be stunned for a while. They can also be jumped on, which allows Mario to reach high points. It could only be defeated if Mario used Yoshi to eat them.
New Super Mario Bros.
Skeeters reappeared in New Super Mario Bros. as rare enemies. In this game, Skeeters would skate around and drop Skull Bombs in the water that are strong enough to break certain blocks. This is helpful, as the explosions can allow Mario to access to new points that he couldn't normally reach.
Super Mario Galaxy 2
Skeeters also appear in Super Mario Galaxy 2. They will try to attack by homing in on Mario. Like most enemies in the game, they could be stomped on to release a coin, or hit with a spin to release three Star Bits. Skeeters can be found in Cosmic Cove Galaxy, Starshine Beach Galaxy, and Throwback Galaxy.