Tunneling response of termites to a pre-formed tunnel.

Subterranean termites move from place to place while foraging by tunneling through soil. During a period of foraging, they are likely to encounter a number of pre-formed tunnels created by, for example, tree roots or the breaking up of a zone of hard or compacted soil. We systematically observed the behavioral response of tunneling termites to such pre-formed, artificially constructed tunnels at widths, W, of 0.5, 1.0, 1.5, and 2.0mm, which mimicked pre-formed tunnels in the field. The two tunnels intersected at an angle, theta (=0 degrees , 10 degrees , 20 degrees , 30 degrees , 40 degrees , 50 degrees , and 60 degrees ) formed between the advance direction of a termite tunnel and the perpendicular direction of a pre-formed tunnel. For W=Wc (=0.5mm) and theta<or=theta c (=30 degrees ), the tunneling termites penetrated the pre-formed tunnel, whereas for all other combinations of W and theta investigated, the termite tunnel merged with the pre-formed tunnel. The implications of these findings are briefly discussed in relation to the minimum size of surface indentation that termites can recognize as a cue to tunnel.