The western gorilla (Gorilla gorilla) has two subspecies: The western lowland gorilla (Gorilla gorilla gorilla) and the Cross River gorilla (Gorilla gorilla diehli), both of which are very similar in appearance, with subtle differences found in the skull and tooth dimensions. Western gorillas are generally smaller than their eastern cousins with shorter hair and longer arms. They tend to be lighter in colour and have a reddish chest and crest adorning their heads. They can climb trees but spend much of their time on the ground, and build nests to sleep in, mostly on the ground, but occasionally in the lower branches of trees.