Meeting Abstract
97.6 Sunday, Jan. 6 Stabilizing falls in confined environments GRAVISH, N*; GOODISMAN, M.A.D.; GOLDMAN, D.I.; Georgia Institute of Technology, School of Physics; Georgia Institute of Technology, School of Biology; Georgia Institute of Technology, School of Physics nick.gravish@gmail.com
Many organisms live and move in underground environments which they have excavated. Such environments may present challenges for locomotion, in part because organisms move within confined and crowded tunnels and chambers. We hypothesize that the ability to engineer underground habitats provides opportunities to facilitate movement. We studied subterranean locomotion of fire ants (Solenopsis invicta, body length BL = 0.35 ± 0.05), which build networks of underground tunnels. In a laboratory experiment we challenged fire ants to climb through 8 cm long glass tunnels (D = 0.1 – 0.9 cm) that separated a nest from an open arena with food and water. During ascending and descending climbs we induced falls by a rapid, short, translation of the tunnels downward. We monitored induced falls over 24 hours in groups from five separate colonies. The confinement ratio (BL/D = α) significantly influenced the ability of ants to rapidly recover from perturbations. The probability to arrest a fall (parrest) within the observed tunnel length fit a logistic equation with parrest ≈ 0 for small α, parrest ≈ 1 for large α, and parrest = 0.5 at α = 0.73, comparable to natural tunnel diameter. The distance fallen prior to arrest (darrest) decreased with increasing α. At small α, ants fell large distances and rarely arrested. At large α, falls were arrested through the use of rapid jamming of limbs, body and antennae against the tunnel walls, arresting in as low 30 ms. We measured the upper bounds of darrest and found that the maximum arrest distance was consistent with scaling predicted from a model of falling in tunnels. Our data indicates that fire ants moving through natural tunnels can employ antennae, limbs, and body to rapidly stabilize falls.
