Parasites in meadow brown caterpillars.

A few people have told me that they have seen white meadow brown butterflies. The reason they are white is that a parasite will sometimes get into their developing larvae during the pupil stage. This is the stage of the metamorphose when the butterflies colours are put into their wings. They have little scales, which are like millions of bags. Blood is pumped sequentially through all of these. The blood carries the pigments, when each colour is completed the scales are sealed, then progressively the scales are filled with the pigment. When the butterfly then emerges they dry out and typically turn into the wings and scales. While the pupae is metamorphosing, a parasite has disrupted the distribution of pigments into the sacks that become scales. Meadow browns are brown for protection, blending in with their natural background. White meadow browns will stick out and be predated.