In MAZEWORLD, a Dark Butterfly is one of the many creatures who poured out from the houses of the antique gods.
It is basically a dark red butterfly. At night she finds for a host, they prefer a male child, when she finds one she enters into her mouth. She lays dozens of eggs Inside his body. The next morning the eggs hatches and many caterpillars began to drink the blood of the kid and to eat his flesh, taking his life to make their perfume magic. Thanks to this perfume magic the boy can remain apparently healthy during the infection, even getting some strange powers, i.e. he can make a dark flower to appear in the soil just by kissing it.
When the caterpillars have taken all the life of the kid, and they have turned it into their magic, they become cocoons. The boy remains falsely healthy, but it is not him but the magic what is animating his dying body.
Finally, the night after a whole lunar cycle since the conception of the eggs, new butterflies are born from the cocoons and they escape from the mouth of the kid, taking with them the magic (and the life of the kid). The new butterfly will find for new kids to invade, and the cycle will start again. The next morning a horrified mother will find a lifeless wooden statue of a kid instead her child, that is the only thing the butterflies left behind.
Certainly, the kid has not really die but sacrificed to create the dark magic of these butterflies, so the kid would still be partially alive, in the form of the butterflies who were born from him. Indeed many infected kids get memories of the previous victims of the butterflies, as their spirits remain as part of their magic. It gives a hope to the saddened parents, but no one knows how to revert the enchantment of a dark butterfly.