It takes 53 days for the pups to grow in the mother before they are born. The mother can produce 5-8 cubs, and sometimes as many as 25 cubs. Both the mother and the father help to raise their young pups. The young females leave the family and form their own groups and the males stay with the family. Arctic foxes form pairs in the breeding season. Litters are born in the early summer. The parents raise the young in a large den under the ground. The pups are born with brown fur. As they grow older, their fur turns white. Arctic foxes sleep with their tails wrapped around themselves. Arctic foxes also have a keen sense of smell. They can smell carcasses that are often left by polar bears as far away as 10 to 40 km.