The main characters in the 'black butterflies story' really depend on the nature of the story. If it's a story about the life cycle of black butterflies, then the butterflies at different stages of their development could be the main characters. If it's a more anthropomorphic story, there could be a human character like a butterfly keeper or a nature lover who interacts with the black butterflies and drives the plot forward. It could also be that there are multiple characters, both human and non - human, all intertwined in the events that revolve around the black butterflies.
There could be many possibilities. Maybe there is a scientist who is studying the black butterflies and becomes part of the story. Or it could be a young child who is fascinated by the black butterflies and follows them into a strange world. Another option could be an old man who has a long - standing relationship with the black butterflies and has stories to tell about them.
Since I don't know the specific 'black butterflies story', it's difficult to say. But it could be the black butterflies themselves as main characters, or perhaps a person who has an encounter with the black butterflies.