Fire ants can make floating rafts on the water’s surface in order to survive the flooding seasons in their native habitat. However, fluids (such as water) are rarely stagnant! Fire ant rafts in nature can be found near the edges of the river where the water flow is slow and grass sticks out from the water surface providing anchors for the ant raft.
Most research in labs focuses on a very different environment: floating rafts on steady water. In this project, we put fire ants on an anchor as a slow water current go across the raft.
We found that fire ant rafts deform into streamlined shapes in the presence of flow!
This is an extremely slow behavior as it took hours to observe the deformation. We did this through careful experimentation and timelapse recordings.
We did not stop at simply documenting the behavior. We use image analysis techniques to identify how they stretch and use agent-based and fluid simulations to find a couple other amazing facts about the behavior:
- This is an active behavior! Neither traditional materials (elastic solids or viscous fluids) nor other bizarre passive materials (viscoelastic materials, think molasses and quicksand ) do this.
- Deforming reduces fluid drag! This is a direct consequence of the streamlined shape. By deforming, fire ants reduce the shear stress required to sustain the raft.
Ko, H., Yu, T.Y. and Hu, D.L., 2022. Fire ant rafts elongate under fluid flows. Bioinspiration & Biomimetics, 17(4), p.045007.
KOLab @ Tufts 