Not all of them, the ones which were spared are developing Reimu babies in stalk or mamumamu, because they don't look like a Reimu, probably Side Titties Reimu and Buri Reimus could have been spared too, they are too different or too ugly.
Death Note works by having both the name and a mental image of the target. Coming to think of it, Deibu could have escaped from death... until the next name is written on the Death Note.
The stalks on this one wilted pretty fast so the mamumamu spawns are killed too. deibus resemble reimu enough and responds to reimu, it's just that they are incapable of pronouncing re in Reimu, so they're killed too.
Left click / right trigger: Kill named target Right click / left trigger: Kill every mutha in the room (you have to hold the button to charge it, then let go)