Facultative mutualism between imported fire ants (Solenopsis invicta) and a legume (Senna occidentalis)

Extrafloral nectaries of Senna occidentalis attract imported fire ants whic h protect the plant against two species of herbivores, the cloudless sulphu r butterfly (Phoebis senna) and the sleepy orange butterfly (Eurema nicippe ). Ant-defended plants had increased growth as measured by plant height and number of leaves, and increased reproductive effort as measured by numbers of pods, numbers of seeds, and weight of pods, compared to ant-excluded pl ants (using Tanglefoot barriers). Survival of herbivore eggs and larvae was reduced in the presence of ants suggesting that ants provide plants with p rotection from larval herbivory thus increasing the amount of primary produ ction which in turn allows greater reproductive output.