BOB HIRSHON (host):
A sweet deal for helpful ants. I’m Bob Hirshon and this is Science Update.
- A leaf-protecting ant. (Enrique Ramirez-Garcia)
The Ecuador laurel tree rewards leaf-protecting ants with a sweet syrup called honeydew. And the more protection the trees need, the more syrup they dish out. As University of Michigan ecologist Elizabeth Pringle explains, the exchange actually involves middlemen called scale insects, which feed on the tree’s sap.
This is a three-way mutualism among the trees and the ants and the scale insects. The sap itself is very sugar-heavy, and so the scale insects excrete a really sugar-heavy honeydew, which is what the ants eat.
The ants, in turn, bite and annoy leaf-eating insects. Pringle’s team found that trees in drier climates host more sap-sucking scale insects,which make more honeydew for more ants. She notes that dry areas have shorter leaf seasons, which makes it worth investing more resources in security. I’m Bob Hirshon for AAAS, the Science Society.