Deceptive color signaling in the night: a nocturnal predator attracts prey with visual lures

The role color signaling plays in the nocturnal condition of the terrestrial ecosystem is currently poorly understood. In general, arthropods active in the night are inconspicuously colored. However, in addition to inconspicuously colored dorsum, several genera of nocturnal orb spiders also have conspicuous ventrum spots. In this study, we tested whether the inconspicuously colored dorsum functioned to reduce spiders' visibility to diurnal predators while the spiders were perching on bark with ventrum spots well concealed. We also evaluated when spiders sit on webs with conspicuous ventrum spots fully exposed, would they serve as deceptive color signals to lure visually orientated nocturnal prey. We first quantified how diurnal hymenopteran predators viewed the dorsum and nocturnal lepidopteran prey viewed the ventrum spots of nocturnal orb spiders Neoscona punctigera by calculating color contrasts. The diurnal color contrast of spiders' dorsum when viewed by hymenopteran insects against bark was lower than the discrimination threshold. However, the nocturnal color contrasts of spiders' ventrum spots when viewed by moths were high. In the field, webs with N. punctigera intercepted significantly more insects than those without. When the color signal of ventrum spots was altered by paint, webs' prey interception rates decreased significantly. These results demonstrate that even in the nocturnal condition certain terrestrial organisms exhibit visual lures to attract prey.