Why are my painted lady butterflies butts red?

The red coloration on the abdomens of painted lady butterflies is likely due to the presence of pigments in their body fluids or waste products. These pigments can be a result of their diet, particularly from feeding on certain plants or flowers that contain red pigments. Additionally, if they are stressed or injured, their body fluids might change color, leading to a reddish appearance. It's a natural characteristic and usually not a cause for concern.