Whereas the double-top wing is almost symmetrical and narrow, being bounded by two s-bends mirroring one another, the less common and less symmetrical double-bottom wing is very wide and  gourd-shaped.  Unlike the double-top wing, which has two short claws like the shorter of the normal claws and one strong double-width central claw, the double-bottom wing is equipped with two of the longer type of normal claw.  Usually this ungainly wing is caught up untidily in the keel petal: if that doesn't happen, it flops over the other wing.  Either way, pollinator's access is blocked.