Crab spider vision improves their prey capture despite low visual system investment

Abstract Crab spiders (Thomisidae) are well-known predators, typically ambushing prey upon flowers and other plants. This style of predation suggests a potential benefit from vision in prey capture by crab spiders despite their comparatively small eyes. However, behavioural evidence on the impact of vision on prey capture success by crab spiders is currently lacking. To address this knowledge gap, we assessed predatory performance in blinded and unblinded crab spiders (Sidymella rubrosignata) co-housed with fruit flies as prey. The results indicate that a lack of visual cues significantly hindered prey capture success. We contextualize this finding using micro-computed X-ray tomography to quantitatively compare the visual optics and central nervous system of S. rubrosignata to other spider species with known hunting strategies (both visual and non-visual). We find that neither high levels of visual system investment nor interocular volumetric specialization are evident in crab spiders, despite the implied contribution of vision to prey capture. Presenting evidence that vision impacts hunting by crab spiders has important implications for our understanding of the elaborate visual ecology of these animals as well as providing key information for future studies on the comparative evolution of eyes and their underlying nervous systems.