43.8 Thursday, Jan. 5 Climbing and falling in confined environments GRAVISH, N*; SALDANA, L; JANKOVSKY, N; GOODISMAN, M.A.D.; GOLDMAN, D.I.; Georgia Tech; Georgia Tech; Georgia Tech; Georgia Tech; Georgia Tech email@example.com
Subterranean animals must rapidly navigate unpredictable and perilous underground environments. Nests of the fire ant Solenopsis invicta (average body length 0.39 cm) consist of a subterranean network of large chambers and tunnels which can reach 2 meters into the earth and house up to 250,000 workers. Laboratory investigations of S. invicta reveal that digging workers typically climb up and down tunnels slightly wider than the largest ant hundreds of times per hour. However the principles of locomotion within confined environments such as tubes have been largely unexplored. We conducted laboratory experiments to monitor upward and downward tube climbing of isolated S. invicta workers and compared the performance to upward and downward vertical-plane climbing (like that found during foraging outside the nest). In both treatments for upward climbing, speed increased linearly with stride frequency with slopes that were not significantly different (ANCOVA; p = 0.31), despite changes in gait and attachment mechanics. Average speeds were approximately 2 BL/sec. On planes the ants used ventral limb surfaces (like tarsal claws) to engage the substrates while in tubes, both ventral and dorsal surfaces of limbs were used. The range of frequency used in the tubes was not significantly different (t-test; p = 0.28) than that for climbing on vertical planes. Compared to upward climbing, animals were able to access a larger range of speeds when climbing downward on planes and in tubes. The fastest downward climbing speeds (8 BL/sec) were achieved in tubes. To reach these speeds ants executed short falls during each step. Falls were arrested through limb and antenna contact with the tube walls, effectively acting as brakes.