It seems that the flowers of my Incarnatas are loaded with house flies and the occasional horse fly, and under some of the leaves I am finding dead flies stuck close to the tips of the leaves. All of my Incarnatas are affected and my biggest spread is on a path leading to the entrance of the house. Not really nice for visitors. All other Milkweeds are not exhibiting the same phenomenon. (Tuberosa, Speciosa, Curassavica)

Thoughts/ideas as to why?