Main body part dominates crypsis in a flower-visiting spider

Camouflage is one of the most common defence strategies. Some crab spiders with uniform colouration have been demonstrated to camouflage on flowers via background matching. However, many more flower-visiting spiders do not have uniform body colour, and whether these species are cryptic on flowers needs more exploration. We investigated this question in a crab spider with a different-coloured abdomen and carapace, Ebrechtella tricuspidata, whose females and juveniles can normally be found on the flower petals of chamomile Matricaria recutita. We conducted predation experiments by using naive chicks as avian predator of E. tricuspidata, to test whether avian predators could detect E. tricuspidata from flowers or leaves of M. recutita. We found that the probabilities of spiders that were detected and attacked were lower when the spider was on a flower petal than on a leaf, which supported the crypsis of E. tricuspidata. Furthermore, the visual modelling from the perspective of chicks showed that spider abdomen matched the flower petal in both chromatic and achromatic contrast and it was unlikely to be detected by avian predators. Taken together, our results indicate that E. tricuspidata is cryptic on chamomile flowers and has a much lower predation risk than on leaves. Importantly, E. tricuspidata is more representative than the species with uniform colouration. Thus, these findings highlight that camouflage may be widespread in flower-visiting spiders.