There is a purple and a yellow variety, which may or may not be a separate species. They can be found in certain areas of long grass, on the multiplayer level Valhalla. They seem to be found in groups of threes, and always stay in the same location each match. One example of a group of yellow butterflies is in the center hill (where the Spartan Laser spawns), at the base of the middle tree on the right (if looking towards the lake base). They are unaffected by any players actions - they cannot be shot or killed and don't react to close proximity of Humans, or Sangheili.