Skip to main content

Defensiveness of the fire ant, Solenopsis invicta, is increased during colony rafting


Colonies of the fire ant, Solenopsis invicta, can survive flood conditions by forming a raft of ants that floats on the water’s surface until the flood recedes or higher ground is found. Having been forced from the protection of their subterranean nests, rafting colonies are totally exposed and are without retreat. I tested the hypothesis that rafting S. invicta colonies would compensate for their elevated vulnerability by increasing their defensiveness. I measured defensiveness using the amount of venom workers delivered per sting (venom dose), since the repellent effects (i.e., pain and tissue damage) of fire-ant venom are dose-dependent. In the laboratory I assayed colony defensiveness before and after flooding colonies from their nests with water. Colonies were consistently and significantly more defensive while rafting (i.e., each colony’s workers delivered higher venom doses when their colony was rafting than they did when it was assayed pre-flood). The larger venom doses of rafting colonies may reduce their chances of being damaged by encounters with other animals by reducing the duration of such encounters through increased repellency. Encounters with S. invicta during flood conditions have the potential to be unusually dangerous; large concentrations of workers are exposed and available for defense, and they deliver significantly larger venom doses when they sting.

This is a preview of subscription content, access via your institution.

We’re sorry, something doesn't seem to be working properly.

Please try refreshing the page. If that doesn't work, please contact support so we can address the problem.

Author information



Corresponding author

Correspondence to K. L. Haight.

Additional information

Received 29 March 2005; revised 20 June 2005; accepted 24 June 2005.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Haight, K.L. Defensiveness of the fire ant, Solenopsis invicta, is increased during colony rafting. Insect. Soc. 53, 32–36 (2006).

Download citation


  • Fire ants
  • Solenopsis invicta
  • rafting
  • stings
  • venom dose