Abstract We describe the genetic control of body color polymorphism in the metallic stag beetle, Cyclommatus metallifer Boisduval. As with many species of sexually dimorphic stag beetles, male C. metallifer exhibit condition-dependent exaggerated growth of mandibles. Another characteristic of this species is that two body colors have been described from both wild and captive bred populations. The two body colors are a commonly observed gold and a more rare black. We performed a simple Mendelian cross of individuals from families that produced only gold offspring to individuals from families that produced only blue-black offspring. All of the F1 hybrid progeny between these two pure gold families and pure black families exhibited the gold body color. The F2 progeny resulting from the crossing of F1 hybrids exhibited a 3:1 gold to black ratio. The backcross of the F1 hybrid to the gold morph resulted in 1:0 gold to black ratio. The backcross of the F1 hybrid to the black morph resulted in progeny with a 1:1...