Imperfect but effective crypsis and flower-visiting strategy in a crab spider

The camouflage of crab spiders on flowers have been extensively studied, primarily focusing on species with uniform coloration. In reality, more than 50 flower-visiting spider species from seven families do not possess uniform coloration. However, there is a lack of exploration regarding them, leaving their cryptic nature uncertain. Additionally, little is known about the flower-visiting strategies employed by spiders at different developmental stages. To address these issues, we investigated Ebrechtella tricuspidata , a crab spider species exhibiting distinct abdomen and carapace colors. Notably, during our earlier field survey, we found that the juvenile spiders appeared on chamomile flowers ( Matricaria recutita ) significantly more frequently compared to the females. Our visual modeling showed that the spider’s carapace on flower petals was detectable, whereas the abdomen matched the flower petals in both chromatic and achromatic contrast, making it unlikely to be detected by avian. Our predation experiment revealed that the probability of being detected and attacked was significantly lower for spiders on flower petals. Moreover, the attacked percentage of juveniles on petals was significantly lower than that of females. Combined with our previous field findings, we predict that spiders in different developmental stages may employ different flower-visiting strategies according to their predation risk. Overall, our study demonstrated that imperfect crypsis of E. tricuspidata on flower prevents avian predation effectively, and the higher presence of juvenile spiders on flowers may be attributed to their lower predation risk. Significance statement Crab spiders are renowned sit-and-wait predators and provide an ideal model for studying animal camouflage. It is widely acknowledged that these spiders exploit flowers of matching hues to deceive their prey. However, there is a pressing need for broader investigations encompassing the camouflage of crab spiders with non-uniform body colors to predators and their flower visiting strategies during ontogeny. To investigate these questions, we conducted avian visual modeling and behavioral experiments. Our findings demonstrated that distinct local body part did not significantly impact overall concealment, suggesting that camouflage is prevalent not only among flower-visiting spiders sporting uniform coloration but also among those with different colored abdomen and carapace. Furthermore, juvenile spiders on flower experienced lower predation risk than females, indicating that spiders at different stages face distinct levels of predation risk. Combined with our previous field findings that juvenile spiders were significantly more commonly found on flowers than females, we predict that spiders may employ varied flower-visiting strategies throughout their developmental stages, where the increasing predation risk leads to a decreased presence of spiders on flowers as they mature during ontogeny.