The five primary feeding modes used by organisms are fluid feeding, filter feeding, bulk feeding, deposit feeding, and phagocytosis, in rough order of commonality. It is very difficult to find a method of feeding which does not fit into one of these feeding modes, although there are many sub-categories within each.
Fluid feeding, the rarest of feeding modes, consists of sucking the fluids out of another plant or animal. Like all other primary feeding modes, it is used by herbivores, carnivores, and omnivores alike. Some well-known fluid feeders include hummingbirds, aphids, spiders, ticks, leeches, vampire bats, and mosquitos. Since many filter feeders feed on blood, they are unpopular among humans and other targeted mammals. Some feed only on the fluids of insects or plants, however.
Filter feeding is the feeding mode found among sponges, moon jellies, krill, mysids, three species of shark, and many whale species, such as the baleen whale. Of all feeding modes, this might be among the easiest: instead of requiring predatory or precision action, the filter feeder just exposes its filters — which take many different forms — and sieves them through food particles. The success of one of the simplest animals, sponges, is a testament to the power of filter feeding.
A feeding mode much more common than the prior two, and the predominant mode for most organisms familiar to us, is bulk feeding. Bulk feeding consists of consuming chunks or the entire body of other animals or plants. Most mammals, birds, fish, and reptiles are bulk feeders, usually consuming plants but sometimes other animals as well. Carnivores specialize specifically in hunting, killing, and eating other animals. Some animals, like humans, are omnivorous, eating both plants and other animals.
Deposit feeding consists of consuming food particles in the soil. Because they usually consume detritus, most deposit feeders are detrivores. A huge range of terrestrial arthropods, including many beetles and mites, are deposit feeders. The earthworm might be the archetypal example of a deposit feeder, as it consumes large quantities of soil and plays an integral part of breaking down dead plant matter into humus. It is considered more common than bulk feeding because of the huge number and diversity of soil organisms that exist.
Phagocytosis is the feeding mode most popular among many unicellular organisms, such as amoeba. It consists of a cell completely enveloping another cell and digesting it using a lysosome. The phagocytes in the human immune system use phagocytosis to consume invaders such as bacteria. Most heterotrophic (non-photosynthesizing) unicellular organisms use phagocytosis as a way to get food.