Dead Reckoning in Tunnel Propagation of the Formosan Subterranean Termite (Isoptera:Rhinotermitidae)

Abstract

Abstract Subterranean termites excavate extensive tunnel complexes in search of resources. The high energetic cost of digging through soil places stringent requirements on the efficiency of tunnel patterns for both search and transport at the time of their initial construction. An efficient spread of tunnels could result from simple diffusion away from a shared origin, but the ability to actively orient the burgeoning tunnels allows for the construction of efficient patterns when faced with the possibility of detours or directional drift. In this study, termite excavators were made to dig through one or two 90° forced turns of varying length that displaced them laterally and changed their heading. When allowed to tunnel freely again, they invariably corrected for the displacement by moving along a vector away from a point of tunnel origination, termed the global away vector (GAV), that was the opposite of a homing vector. Through the elimination of reliable allothetic cues, idiothetic dead reckoning was shown to be sufficient to orient tunnel headings. Excavation in termites was not coordinated solely by stigmergy, because tunnelers did not rely on local cues alone while digging, but the removal of soil from sites at the tunnel tip was governed by their ability to generate a GAV through dead reckoning.