Lab: Hu Lab Biolocomotion (Publication: https://doi.org/10.1088/1748-3190/ac6d98)

Video

• Example Experiment

• Using Image Processing to abstract the outline of ant raft

Figures

Figure 3. The activity of ants at the raft’s perimeter . (A) Schematic showing ants exploring the boundary of a raft. The blue arrow indicates the direction of water flow. (B) Steps for calculating the ant activity level $Δr(θ, t)$, the difference in radii of the rafts at two points in time. The sample graph on the right shows the relationship between $Δr(θ)$ and angle $θ$ for a single instant in time. Heat maps of $Δr(θ, t)$ for rafts (C) in still water and (D) in flow. The dotted lines mark the leading and trailing edge of the raft. Video of ant raft boundary change over time: https://youtu.be/9UhUbt_B6sk

Abstract:

Fire ants survive flash floods by linking their bodies together to build waterproof rafts. Most studies of fire ant rafts consider static water conditions, but here, we consider the influence of flow. In particular, when floating on shallow water, the raft can run aground on vegetation, generating stresses in the raft as the water continues to flow around it. In this combined experimental and numerical study, we film the 10 h response of a fire ant raft caught on an anchor and subjected to water flows of 6 cm s−1. In this situation, ant rafts elongate from circular to more streamlined shapes, doubling in aspect ratio before eventually contracting back into smaller circular shapes as they enter dormancy. Ants in upstream regions of the raft exhibit less exploration activity than those downstream, suggesting that ants migrate to areas of lower fluid stress. While the raft is rough, hydrophobic, and heterogeneous in height, we may gain some insight by performing both fluid-structure interaction and agent based simulations on smooth rafts. Elongation to the degree observed is associated with a 48% drag reduction. Moreover, a purely elastic raft does not elongate, but conversely increases its bluff body cross-sectional area. We conclude that ant raftsmust reconfigure to generate the elongated shape observed. This work may provide insights into designing intelligent robotic swarms that can adapt to fluid flows.

Publication: