The tails of some monkeys are so strong that they can hold their own weight. All monkeys have tails, but all monkeys do not have prehensile tails. Monkeys that do have prehensile tails use them like an extra arm or leg. Female spider monkeys carry their babies on their bellys for the first month of their life and then the babies ride on the mother’s lower back, holding on with his tail, for the next nine months. Spider monkeys are the favorite pet monkeys in Latin America because they are friendly and smart. They are considered a little above gorillas in animal intelligence. Spider monkeys and howler monkeys are the largest monkeys in the American tropics. Spider monkeys’ brains are twice the size of the howler. It is thought that spider monkeys have a larger brain because of their complex social life and their specialized diest of ripe fruit. Searching for fruit and testing its ripeness is a multisensory task that requires a lot of brain power.