The Killer Bee is an enemy in the Castlevania series. It is a giant bee with a stinger that can easily pierce and kill.
Killer Bees are gigantic and monstrous versions of common bees. Their abdomens are elongated and appear to be swollen, perhaps from the amount of poison they carry inside, giving them an aspect more akin to wasps.
The ones in Circle of the Moon, while uncommonly large, still resemble the common insects they're based upon, although featuring a blue exoskeleton. They're strikingly fast and difficult to avoid. This variant will inflict Poison status to Nathan if they manage to sting him.
The ones found in Portrait of Ruin are more dreadful, as the shape of their heads combined with their big mandibles make them look as if they had a human skull, not to mention the hives from where they spawn also resembles an upside down skull. While not as fast or poisonous as their Circle of the Moon counterparts, this variant relies more in numbers and may overwhelm the heroes should they let them populate the room.
These giant insects are initially encountered hovering in place until approached, at which point they make a lightning fast strike which can be difficult to avoid and which inflicts Poison status if successful. They can be killed fairly easy with ranged attacks, though.
The Killer Bees found in Portrait of Ruin are generally slower, although they come out in endless hordes from inside of Bee Hives found throughout the Forest of Doom. Destroying the hives will prevent more bees from spawning.