Milkweeds have very distinctive flowers, with unique shapes and features. I guess it shouldn’t be surprising that their pollination story is equally interesting.
Common milkweed (Asclepias syriaca) flowers. Lincoln Creek Prairie – Aurora, Nebraska.
First, milkweed flowers don’t produce thousands of of individual pollen grains that can each get carried away to other flowers by visiting insects. Instead, milkweeds have what are called “pollinia”, or waxy masses of pollen that are designed to stick to insects. You might think that a flower with a specialized pollen structure like that would have a system to make it easy, or even automatic, for any visiting pollinator to pick up and deliver that pollinia to the next flower. After all, there are countless stories of flower types that facilitate pollination by forcing visiting insects to hit the right spots as they forage for nectar and pollen.
With milkweeds, not so much.
The Prairie Ecologist 