Commensalism is a relationship between two organisms where one receives a benefit or benefits from the other and the other is not affected by it. In other words, one is benefited and the other is neither benefited nor harmed.

Commensalism in Nature

• Anemonefishes or clownfishes – These live amid the tentacles of the anemones which protects them from predators. Predators are poisoned by the nematocysts of the anemones.
• Atlantic puffin – These puffins use burrows for nesting that were made by rabbits.
• Bacteria (Acetobacter oxydans)  – These make fructose by oxidizing mannitol. Other species can metabolise fructose, but cannot metabolise mannitol.
• Barnacles – These will attach to whales or mollusk shells in order to be where food is available. This also acts as transportation for them and safety.
• Burdocks – These are common weeds and dispersal of their seeds is critical to their life cycle. Their seeds have spines or spines with hooks that will allow them to be picked up in the fur of animals passing by. They can also attach to the clothing of humans.
• Cattle egrets – These birds live near cattle because when the cattle graze, their movements stir up insects. The birds have their insects and the cattle are unaffected.
• Epiphytes – These are a species of plants that grow on some woody plants. Epiphytes get their nutrients from the air and use the plants for support and access to sunlight.
• Flatworms – A flatworm attaches to a horseshoe crab and it will eat the crab’s food. This does not harm the crab.
• Gila woodpecker and small animals – The woodpecker makes holes in Saguaro cacti to get food. The holes become homes for small mammals and birds.
• Gobies – These live on sea animals, often changing color to blend in. They do this for shelter and protection.
• Golden jackals – Golden jackals that are no longer in a pack will trail a tiger so it can feed on what the tiger kills.
• Hermit crabs – These crabs have to find shells for shelter and use various snail shells. These shells are available because the snail has died; so, the snail is not affected.
• Mites – Mites will attach to wasps, flies or beetles for transportation.
• Monarch butterflies – These orange and black butterflies eat larva on milkweeds. This larva tastes bitter and is poisonous to vertebrates and so birds learn to avoid monarchs.
• The mosquito Wyeomyia smithii – The larvae live inside the plant Sarracenia purpurea and does not harm the plant.
• Orchids – Some orchids grow on trees and that does not harm the tree.
• Pilot fish – Pilot fish live around sharks, sea turtles and rays and eat the parasites that live on them as well as leftover food they do not eat. Young pilot fish gather around jellyfish and seaweeds.
• Pseudoscorpions – These look like scorpions but do not have a sting. They will sometimes hide under the wing covers of large beetles, like the cerambycid beetle. This not only allows them to be dispersed over a large area but protects them from predators.
• Remora sharks – These have a disk on their heads which allows them to attach to a large animal, like a shark. As the shark eats, any extra food floats by and they can unhitch themselves and eat.
• Seedlings – Nurse plants offer protection from frost and herbivores so the seedlings can grow. An example is bunchgrasses needing mesquite trees as nurse plants.
• Titan Triggerfish and smaller fish – As triggerfish feed, they move large rocks, bite off pieces of coral and stir up the sand. Since smaller fish cannot move large rocks, this presents an opportunity for them to feed.
• Tree frog – The frog uses plants or trees for protection from the rain.

These examples of commensalism in action show the symbiotic relationship between organisms. For more examples check out Examples of Symbiosis.