Passive debris cloaking in beetles provides non-visual camouflage against predatory ants

Our understanding of visual camouflage has increased dramatically in recent years, however we know less about anti-predator defenses that exploit senses other than vision. Low light habitats, such as leaf litter, are more commonly dominated by predators that rely on chemical, tactile, and other nonvisual cues. Passive debris cloaking is a trait found in several arthropod groups that reside in low light habitats and appears as a layer of environmental debris that covers the cuticle. This debris accumulates passively as the organism moves through its habitat, generally via the secretion of adhesive compounds through specialized pores. We hypothesized that passive debris cloaking is a form of non-visual camouflage, and tested this experimentally using zopherid beetles as a model. Zopherid beetles are highly diverse in Aotearoa New Zealand and include many species that exhibit passive debris cloaking. By exposing zopherids with varying degrees of cuticular debris to colonies of foraging predatory ants, we found that passive debris cloaking (1) reduces detection by ants, (2) reduces the probability of attack if detected, and (3) is most effective when interactions occur on natural backgrounds. Our results provide evidence that passive debris cloaking is a highly effective form of non-visual camouflage, suggesting non-visual camouflage may be more prevalent in low light habitats than currently appreciated.