Differential frequency of autotomy in two colour morphs of the grasshopper Atractomorpha lata (Orthoptera: Pyrgomorphidae) on dense and sparse grass substrates

Background colour matching is considered highly effective in preventing the detection of an animal by visual predators. In a grasshopper species with green-brown polymorphism, a green morph on grass and a brown morph on bare ground or dead litter may be difficult for visual predators to distinguish from their respective backgrounds. However, few studies have examined the effects of background colour on the predation susceptibility of green and brown morphs of grasshoppers under natural conditions. In this study, the frequency of injuries including autotomy in the green-brown polyphenic grasshopper Atractomorpha lata was compared between two substrates: dense green grass and sparse grass (i.e., mixed cover consisting of 50% green grass and 50% bare soil or dead litter). More than half of injuries were hind-limb autotomy. The frequency of injuries was higher on dense grass for the brown morph than for the green morph, but on sparse grass it was higher for the green morph than for the brown morph. Because autotomy in orthopterans is almost always caused by birds, we conclude that background colour matching in A. lata functions as camouflage against predators with colour vision, such as birds.