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The most massive land animals in the world all eat little stuff, grass and leaves. And almost all of the most massive aquatic animals also eat something itty-bitty, tiny crustaceans called krill. Why do such big things eat such small things? Hi, I'm David and this is Minute Earth. The most ginormous animals all need to eat a huge amount of calories to fuel their massive bodies, but there aren't enough big super calorie dense meals around for them to eat. And even if there were, the giants massive bodies aren't mobile or agile enough to actually capture that food. Instead, these mega creatures meet their mega calorie quota with something that's super abundant and requires almost no effort to procure, little pieces
of grass and leaves. And for our purposes, we're going to consider leaves to be little even if they do come off of bigger things. And sure, leaves and grass aren't very calorie dense compared to things other animals eat, but the giants giant digestive tracts can hold a lot of them at once. We're talking hundreds of kilograms. Plus, the bigger an animal is, the longer the food stays in its digestive system and the more microbes there are in there to break it down. All of that means that the giants are able to wring a lot of calories from grass and leaves, enough to meet their huge calorie demands. The abundance and ease of finding leaves and grass and the specialized digestive systems to deal with large quantities of them are why,
at least on land, you see the same pattern in every biome. The very biggest animals are herbivores. Even back in the day when dinosaurs roamed the earth, the biggest animals weren't predators like T-Rexes, they were lumbering leaf-eating vegetarians. But what about the ocean? Like their counterparts on land, sea giants like blue whales are relatively unagile and have giant guts. So, it makes sense that they'd eat the ocean equivalent of grass, huge blooms of tiny plant-like microorganisms called phytoplankton. But these ocean behemoths need so many calories every day that phytoplants, even lots and lots of them, just aren't calorie dense enough to meet the demand. Luckily, those big phytoplankton blooms attract something
else, billions of calorie-packed krill that come together to graze in huge, slow-moving, easy-to-find swarms. A blue whale that lunges back and forth through a swarm can easily take in more than enough calories to power its huge body. The equivalent on land would be if there were huge slow-moving swarms of grasshoppers that elephants could munch on instead of the grass itself. In that case, the pachyderms could pack in even more calories and likely get even bigger. Either way though, the same truth holds. For the biggest animals on Earth, it turns out, food things come in small packages.
