Measurement of the Time Required for a Termite to Pass Through Tunnels with Different Curvatures

The subterranean termite, Reticulitermes speratus kyushuensis (Isoptera: Rhinotermitidae), excavate complex tunnel networks below the ground for foraging. The tunnels are either curved or meandering. In our previous study, results showed that termites passed smooth—rounded corners faster than they did around sharp corners. Smooth—rounded corners can be mathematically quantified by the curvature, representing the amount by which a geometric object deviates from a straight line. The present study explored how the time spent inside a tunnel changes in accordance with the degree of tunnel curvature. To do so, artificial tunnels with different curvatures were constructed in acryl substrates. Tunnels were 5 cm in length with widths of W — 2, 3, or 4 mm, and the distance between the two ends of the tunnel was D = 2, 3, 4, or 5 cm. A higher value of D signified a lower curvature. The time (τ) taken by a termite to pass through the tunnel was measured. In the case of W = 2 mm, the values of τ were statistically equal for D = 2, 3, or 4 cm, while τ for D = 5 cm was significantly lesser. In the case of W = 3, τ was statistically more for D = 2 and 3 cm than it was for D = 4 and 5 cm. For W = 4, τ was statistically equal for D = 2 and 3 cm, while τ for D = 4 cm was relatively shorter. Interestingly, the value of τ when D = 5 cm was statistically the same as D = 3 or 4 cm. These resulted from two types of termite behavior: biased walking and zigzag walking.