Mimicry
This may explain cases such as Papilio dardanus, an African swallowtail, whose females mimic a number of unpalatable species from the Danaidae: survival is higher when each mimetic form is rare relative to its model. The advantage is probably greater for the females, because males do not show the mimetic patterns; sexual selection probably helps to maintain this difference. These, and other issues, have been researched for many years.