Makai insects were demon bugs used by the Saint Beast Suzaku to turn humans into an army of mindless zombies for his own use. The insects can't survive outside Spirit World's barriers without the pulse from the Makai Whistle.
Makai insects were large insects native to the Demon World. They were winged and six legged. They possessed a long needle like mouth, much like a mosquito's, that they used to bite humans, possess them,and turn them into mindless zombies. They had two red markings, on their body, in front of their wings.
Suzaku controlled the Makai insects through the Makai flute. He used them to possess humans and turn them into mindless, violent, zombie-like beings.