Meeting Abstract
119.7 Tuesday, Jan. 7 11:45 Pellet formation and transport by fire ants MONAENKOVA, D.*; GRAVISH, N.; GOODISMAN, M.A.D.; GOLDMAN, D.I.; Georgia Institute of Technology, School of Physics; Georgia Institute of Technology, School of Physics; Georgia Institute of Technology, School of Biology; Georgia Institute of Technology, School of Physics dmonaen@physics.gatech.edu
The red imported fire ant, Solenopsis invicta, builds deep nests underground which house thousands of individuals. Nest construction for fire ants is a complex process consisting of soil excavation and transport from the nest depths to the surface through a network of self-excavated narrow tunnels. Thus, nest builders confront a dilemma. Rapid nest construction requires the excavation of large soil pellets. However, heavy traffic within naturally confined spaces favors formation of small pellets. We studied the strategy used by fire ants to construct nests in soils that differed in moisture content, which can influence pellet integrity during formation and transit through the nest. In our experiment 30 ants were isolated in a transparent plastic container filled with wet simulated soil (0.25 mm glass beads). The soil moisture content W was prepared to W=0.01 or W=0.1 by mass. Tunnel construction occurred along the transparent container walls and was recorded with a high speed camera in order to determine the number of grains carried by ants, ant mobility and social interactions between individuals. Our observations revealed that ants used mandibles, limbs and antennae in a stereotyped excavation behavior to remove, form, and transport soil pellets. Surprisingly, W had no significant effect on the average pellet size (p =0.078). Although some ants were capable of carrying up to 22 grains, the mean pellet was composed of 6 ± 2 grains in both W treatments (N= 320 observations at W=0.01 and N=524 observations at W=0.1). We hypothesize that the preferred pellet size is not determined by soil cohesion but instead is engineered for transport in the confined and crowded conditions.
