On Peonies and Ants

It is just about that time when peony buds burst forth and put on their late spring display. My mother loves her peonies and she gets very excited every year when they bloom. It's adorable. However, she has always been disgusted by the amount of ants the peonies attract. Indeed, many people all over the internet seem to feel the same way. Growing up, I always wondered why the ants seemed to swarm all over peony buds, so I decided to look into it a little deeper.

There are many sources out there that claim that peonies need ants in order to bloom. To me, this seems very maladaptive on the part of the peony. The genus Paeonia is represented in Asia, Southern Europe and parts of western North America. I am going to assume that the ant/peony relationship didn't start in the garden so it's roots have to be somewhere in the evolutionary history of the plant. What sense does it make for a plant to produce flower buds that excrete sticky sugars that keep them from opening until something cleans the sugars off? In fact, despite anecdotal reports, peony buds will open without ants. So then why does the plant bother to produce sugars that attract ants?

Interestingly enough, despite a good amount of searching, there is not a lot of research done on this subject but the answer to this question can come from looking at how ants interact with other plants and animals. Species like partridge pea (Chamaecrista fasciculata) and wild senna (Senna hebecarpa) have special glands on their stems that produce sugary secretions that attract ants. Also, aphids so famously excrete honeydew that ants can't resist. In each of these cases, organisms are using the ants' natural tendency to guard a food source. The ants will viciously attack anything that threatens this easy meal. Because of this, other insects are driven off.

It would seem to me that the peonies are doing just that with their flower buds. By secreting a sugary substance during their development, the plant is recruiting ants to protect the flowers, which in the plant kingdom, are the most precious part of the plant. It takes a lot out of a plant to flower and the threat of herbivory is ever present. If an insect tries to take a bite out of a bud, the ants quickly swarm it and drive it off. It's a win win situation. The ants get an easy, high-energy food source and the plant suffers less damage to its reproductive organs.

The scary part to me in researching all of this is plethora of information out there on how to get rid of the ants. People go through chemical after chemical to rid their peonies of ants when, in reality, the ants are some of the best friends a peony could have! So leave those ants alone and enjoy the free pest removal services they provide every spring!

Photo Credit: Sylvatica

Further Reading:

http://www.youtube.com/watch?v=Gnm2nV_nwOk