What animal has the highest population on Earth?

== == There can be a million tons of krill in a singel swarm. Krill are considered keystone species near the bottom of the food chain because they feed on phytoplankton and to a lesser extent zooplankton. The number of plankton EASILY outnumbers all other animals on the earth - unless you get into bacteria. Plankton are found in every part of every ocean - and whales often eat millions of them in a single day!!! Hard to see anything more popular than plankton!! "Plankton are tiny open-water plants, animals or bacteria. The name, like the word planet, is derived from a Greek root that means, "wanderer." These organisms range in size from microscopic bacteria and plants to larger animals, such as jellyfish. Plankton generally have limited or no swimming ability and are transported through the water by currents and tides."