Post by Adam Cotton on Feb 23, 2021 0:51:41 GMT -8
Some degree of asymmetry is not overly rare, but not common either. It is caused by incomplete formation of the pupal case. All of the adult appendages are delineated on formation of the pupa, which can be viewed as a mold for the adult. So if the pupal wing case on one side does not completely cover the relevant area of the pupa that wing will be smaller than normal or misshapen when the butterfly emerges and expands its wings. Of course in extreme cases the adult is unable to fly, so those are not seen in the wild.
Similarly antennae and legs are all formed from the pupal mold, so if one antennal sheath is shorter than normal in the pupa the resulting antenna will be shorter than the one on the other side.