Rapid colour change in spiders

Abstract

During the last century, there were records of physiological rapid colour change in about 20 spider species from five different families. However, the underlying mechanism has not been solved up to now. These spiders have light guanine markings on their opisthosoma which more or less disappear when they drop from the web. For spiders, colour change is an effective way to confuse predators and to remain undiscovered after having fallen on the ground. The relevant species and the studies referring to them are introduced. In the linyphiid spider Floronia bucculenta, muscles connected to the guanine-storing parts of the midgut diverticula were recently found. These muscles are arranged like a grid and seem to cause the rapid disappearance of the white guanine dots in this species. In a related species which is unable to change its colour, no similar muscles can be found. The colour change of F. bucculenta and the morphological findings are presented.