Behavioural choice and background matching facilitate camouflage in the European garden spider

Visual camouflage via background matching involves a variety of adaptive
traits to maintain crypsis, including intraspecific color variation,
behavioral choice of substrates, and color change. These non-mutually
exclusive solutions frequently act together to conceal and deceive prey
and enemies. Here, we combine field observations, image analysis, and
laboratory experiments to investigate which processes drive camouflage in
the garden cross spider (Araneus diadematus), a species with body
coloration that varies in shades of brown. We demonstrate that A.
diadematus does not change color significantly, at least within the same
instar, when retained on substrates of different coloration. However,
there is strong behavioral selection through active substrate choice
across spiders for color-matching substrates (dead brown leaves over green
leaves) when offered a choice under laboratory conditions. Similar
background selection also apparently occurs in nature, where spiders were
often observed on brown leaves, even though they are less common than
green ones. In general, vision modeling shows that there is a high overlap
in the diversity of brown shades (from pale to dark) between spider bodies
and dead leaves available in the environment. Image analyses also revealed
that spiders fine-tune their camouflage on an individual level by matching
the tones (from pale to dark) of their host leaves. Therefore, we
demonstrate how behavior coupled with variation in color phenotypes
facilitates camouflage at different scales.