Commensalism, another form of symbiotic relationships, is defined as symbiosis between unrelated organisms: the relationship between organisms of two different species in which one derives food or other benefits from the association while the other remains unharmed and unaffected. As one can see, it is far different than parasitism.

If we start by looking at the human body in which we would be considered the host, we find all the thousand of bacteria that live on our skin and within our digestive tract and respiratory tract. They live because there is a beneficial environment for them…..food, moisture, and a place to reproduce. Most of these species do no harm to the human body, but there are some that cause unpleasant body odors which really are not harmful just offensive to one’s nose.

There are also several species of protozoans that live with the intestinal walls that act as decomposers of our food. They break down our food so the nutrients can be absorbed by our body. These same species live also in all mammals.

Cellulose in wood and some plant materials is a non-digestible substance, however, termites do not seem to have any problems digesting it. How can that be? There is a small protozoan that lives in the gut of the termite, and a few other insects, that can digest cellulose. These protozoans depend upon the termite to eat the cellulose in order for them to survive, and the termite uses the by products of this process for nourishment. Think of all the hundreds of dollars that could be saved if we could eliminate that protozoan from the termite.

There are several form of spiders (crab spiders) that live on flowers that blend in with their petals. When a pollinator lands on the flower it becomes a spiders meal. The flower really does not know the spider id there, but the spider benefits.

The cattle egret lives along side of many different animals and sometimes a re found living or riding on them. They do no harm to these animals, however, when the animal walks, the egret gets a meal of all the insects that are scared up in the grass.

The ox pecker, a colorful bird found in Africa riding on the backs of most animal of the plains there. It does no harm to these animals, but it gets its meals from them. There is a fly that deposits its eggs under the skin of these animals, usually on the legs, As this insect develops it migrates through out the body of the animal and usually ends up under the skin on the back. By this time it has become a large maggot or grub. The ox pecker sees this bulge where the maggot exists and sit and waits for it to emerge. When it does it gets a big meal.

Everyone has seen the big sharks and manta rays on TV. There are always remoras hitched to them along for the ride. Remora a very poor swimmers, and because of that fact have turned their dorsal fin into a sucker type apparatus. They use this fin to attach to bigger fish, and thus, they move around the ocean with ease with their host doing all the work. However, when the shark feeds, and small pieces of its meal float around the shark…the remora releases its grasp and picks up these small morsels and when full again attaches. One can see there is no harm to the shark, but the remora benefits greatly.

There are many such stories in the oceanic invertebrate world. Worms that cohabitate in the same tube. One gets security and food while the other is unharmed. Snails that look like corals and live on the gorgonians. They get the security through camouflage, and the gorgonian is unharmed. Snails and shrimp that live within the mantle of clams, thus again gaining security from predators, while doing no harm to the clam.

Commensalism takes place in many forms, too. Look at the little 1 inch fish that stop the construction of many dams in the Southeast….the snail darter. This little fish was becoming extinct because the snails were dieing because of pollution of the rivers. With out the snails, this little fish had no place to lay its eggs. It extends its ovipositor under the lip of the shell of the snail, and deposits its eggs there, The snail circulates fresh oxygenated water through out its shell and keep the eggs safe. As the babies hatch they then take refuge in the bed of the stream, but they are safe through incubation.

Another such animal of the ocean is the barnacle. Whales have barnacles growing on them. The do no harm to the whale but benefit from the attachment. The whale carry the barnacle around the oceans, providing a varied plank tonic food source on which the barnacles survives.

In the plant world……We all have seen lichens growing on trees. Lichens are a green algae and a fungus growing together. The green algae provide the nourishment for the fungus to live. The fungus does not harm the algae in any way. Together they become a lichen. When this lichen grows on trees, the trees provide space for them to grow and the tree is not harmed.

There are hundreds of such forms of commensalism in the world. Most are a matter of security in some form or a means adaptive for the collection of nourishment of the animal.

Studying about our natural world makes it so much more interesting than just the beauty that is created by all the life that is there to photograph. It is such an interesting endeavor to do both, and in doing so, one sees things from a different perspective. It then becomes a benefit to the user. OH! Would that be commensalism?