Squirrel monkeys are slender built monkeys that can be found in the tropical jungles of Central and South America. These diurnal monkeys are said to be the most intelligent of all the monkeys. They are omnivorous feeding on both small animals, insects and plant matter. Due to their constant movement, they are referred to as nervous monkeys. Their average size is about 10.6 inches and their typical lifespan is about 15-20 years.