Scarabs are a family of beetles, scientifically called Scarabaeidae. Most are brown or black in colour, but many, generally species that are diurnally active, have bright metallic colours, measuring between 1.5 and 160 mm (0.059 and 6.3 in). The antennae of most species superficially seem to be knobbed (capitated), but the several segments comprising the head of the antenna are, as a rule, lamellate; they extend laterally into plates called lamellae that they usually keep compressed into a ball. Then, when following a scent, such a beetle fans the lamellae out like leaves to sense odours.