【生態】鳥の糞のふりをするクモ

A spider that disguises itself as bird droppings to avoid predator attacks is described in Scientific Reports. The study shows that web decorations and body colouration on the orb-web spider Cyclosa ginnaga are indistinguishable from bird droppings to the eyes of its predators.

Many animals use distinct body shapes, colours and patterns to avoid predators, either by blending into their backgrounds, mimicking other animals, or masquerading as an inanimate object. The C. ginnaga spider has a silver body and creates a white disc on its web that functions to attract prey, but these characteristics may also make them conspicuous to and predatory wasps. To the human eye, the size, colour and shape of the body against its decoration resemble bird droppings, and it has been hypothesised that these spiders masquerade as bird droppings to avoid predation. I-Min Tso and co-authors support this theory by showing that the spiders and their web ornaments look almost identical to bird droppings, both in colour and in size, when viewed under conditions that replicate how wasps may see them. They also observed that wasp attacks were far greater on spiders that had either their webs or bodies blackened with carbon powder than those who had their normal body colouring and webs exposed.

Thus, these findings suggest that the body and web decorations of C. ginnaga might combine to protect it from predators by forming a bird dropping masquerade, although the authors suggest that this conclusion be further tested against alternative explanations.