A guest post by Anne Stine, one of our Hubbard Fellows. All photos are by Anne.
I was scouting for native seeds in our sand pit restoration across from the crew quarters when I noticed a fascinating pollinator-plant interaction. This activity would’ve been best captured on video with a high quality zoom (which I did not have), but I was able to take pictures. Bumble bees, and only bumble bees, were fighting their way into great blue lobelias along the edge of our restoration. Meanwhile, their neighboring cardinal flowers were visited by butterflies exclusively. Why, and how, were these two closely related flowers so specialized with their pollinator partnerships?
First, let’s consider the great blue lobelia (Lobelia siphilitica). The architecture of this flower insures that only burly bumble bees can gain access to the pollen and nectar. Some other insects “cheat” and chew holes in the flower to by-pass the petal-gate, but bumble bees are their primary visitors. Watching the bumble bees pry open the flowers was entertaining. First, they climb onto the flower’s extending ‘tongue’. Then, they push aside the two top petal ‘lips’ and dunk themselves head first into the flower. Their front half is completely inside the blossom. Only their bottoms and back legs stick out. They clamber up the stalk, climbing from flower to flower until they reach the top, and then they fly off to visit a neighboring plant. Because great blue lobelia seems to grow in patches, this is an efficient operation for both bee and blossom. The bees act drunk on nectar, and the flowers are practically guaranteed a thorough pollination.
Conversely, cardinal flower (Lobelia cardinalis) is traditionally considered to be a ‘hummingbird-specialist’ plant. We are just outside the range of the ruby throated hummingbird here on the Platte River Prairies. Instead, butterflies with their long tongues seem to have taken over the majority of the nectaring and pollination duties. Or perhaps cardinal flowers in this part of Nebraska predominately self-pollinate. At any rate, bees weren’t the major customers on cardinal flowers. Cardinal flowers were visited by butterflies.
How strange that these two wetland con-generics, great blue lobelia and cardinal flower, could grow in intermingled patches and still rely on totally distinct pollinator communities. Nature is weird and wonderful.
This monarch had the choice between blue lobelia and cardinal flower. She chose cardinal flower. So did all the other butterflies.