The single species of wolverine is a heavily built animal, immensely strong for its size and capable of killing animals larger than itself. Although largely carnivorous, wolverines also feed on berries. They are solitary animals, mainly ground-dwelling, but they can climb trees. Each male holds a large territory with 2 or 3 females and mates in the summer. The female wolverine bears 2 or 3 young in the following spring, usually after a period of delayed implantation. Delayed implantation is an interesting phenomenon allowing animals to mate at the ideal time and bear young at the ideal time, even though the intervening period is longer than their actual gestation. The fertilized egg remains in a suspended state in the womb, and development starts only after the required period of dormancy. The young suckle for about 2 months and remain with their mother for up to 2 years, at which time they are driven out of her territory. They become sexually mature at about 4 years of age.