The flowers are clearly swollen, often moreso than ungalled buds, and they stand out amongst the rest of the flowers on the umbel. Galls contain several orange to cream-colored larva. The petals are often browned or otherwise visibly damaged. It is not known whether the pale and orange larva represent different or the same species. Likely found on other Asclepias species. This species has also been observed on Asclepias tuberosa, however it is not clear whether or not the tuberosa galls are the same species as the syriaca galls. Observed in Ohio, Massachusetts and Virginia in June.
In July, Ray Gagne identified the galls as being formed by an unknown member of the genus Contarinia.