A juvenile octopus grows at a rapid rate, perhaps because of its short life span. Extremely effective at turning the food it eats into body mass, a young octopus increases its weight by 5 percent each day. By the end of its life, an octopus will weigh one-third as much as all the food it has eaten [source: The Economist]. The common octopus only lives an average of three to five years, though, so it doesn't have much time to waste.