The illusion of infinity: Acoustic black holes in wood deceive termites
Vibrational signals produced during feeding are fundamental to termite behaviour, yet their function in regulating collective foraging remains unclear. In this study, we combine bioassays, micro-CT imaging, and elastic wave modelling to investigate how the subterranean termite Coptotermes acinaciformis evaluates wood through structural wave propagation. Using an axially excited Acoustic Black Hole (ABH), a tapered geometry that minimises wave reflections and effectively mimics an infinitely long food source, we show that termites preferentially attack longer wooden dowels and, remarkably, also lighter ABH-modified dowels. Micro-CT scans revealed feeding concentrated in the dowel core, coinciding with the region of maximum stress predicted by the models but where echo return was minimal. These results indicate that termites assess wood size through bite-induced echoes, analogous to echolocation in bats and dolphins, and preferentially exploit core regions of trunks and branches, thereby accounting for the tree-piping behaviour of termites. The reduction or absence of reflected waves may thus act as a cue that stimulates collective stigmergic foraging. From an applied perspective, ABH-inspired structures could form the basis of novel, chemical-free lures for termite management.