What Is Symbiosis?

Category: Feeding Behavior.

Living together, cohabitation, this is the simple explanation of what the word symbiosis means. The only time a relationship can be considered symbiotic, however, is when it occurs between different species. There are three categories of symbiosis:

  1. Commensalism: that is when one species benefits without affecting the other.
  2. Mutualism: both species benefit.
  3. Parasitism: one species benefits and the other one is harmed.

Symbiotic relationship between ants and aphids. Ants provide protection from ladybugs or other insects while the aphid excretes sugary honeydew as a reward. © Matt Cole.

Another type of symbiosis

There is also a fourth category but it is not one of physical intimacy and that is mimicry. This is when one species takes on characteristics of another so that they can reap the benefits of that species. This is seen with the Viceroy and Monarch butterfly and the Banded snake and the venomous Sea snake. The Viceroy butterfly and the Banded snake both have markings similar to the other animal so that predators will be fooled. It is a matter of survival.

Three common types of symbiosis

There are three types of symbiotic relationships in nature. Let’s look at each one with a few examples of each.


This type of relationship is generally seen in two species where one member is looking for protection or transportation. This only works when the other species has an effective defense mechanism or are prolific travelers. A great example of this would be the relationship between the anemonefish (or commonly known as clownfish) and the sea anemone.

Common Clownfish (Amphiprion ocellaris) and the Magnificent Sea Anemone (Heteractis magnifica). © Janderk.

Examples of commensalism

The sea anemone has tentacles that are lethal to most of its predators. The colorful little clownfish has become immune to this poison and live within the safe confines of the anemone. On land, commensalism is evident with the relationship that has developed between the egret and cattle. These birds eat insects that are displaced while the cattle are foraging. Neither animal is harmed by the presence of the other. This type of symbiosis can be as simple as a spider building its web in a tree or a hermit crab using a vacated shell as a home.


This type of symbiosis is where both parties get something from the relationship. One of the best examples of this is the relationship between man and his best friend. The dog-human relationship evolved out of mutual need, the dog gets food and love, he provides the human with a worker on farms, an alarm system, and in many instances protection from harm.

Pilot fish and the Whitetip shark. © Peter Kölbl.

Examples of mutualism

Another example of this type of symbiosis is the relationship some smaller fish have with larger fish. The remora and pilot fish both have a mutualistic relationship with large fish like whales and sharks. They swim along with these predators without fear, because they know they serve a valuable purpose in their lives. The remora shark removes parasites while the pilot fish receives a free meal when the shark eats.

The shrimp and goby fish

The blind tiger pistol shrimp and the yellow watchman goby. The goby is the lookout and the shrimp maintains a burrow for the pair. © Haplochromis.

The blind tiger pistol shrimp and the yellow watchman goby also have a mutually beneficial relationship. The shrimp is practically blind. When the shrimp makes a burrow, he and the goby move in and when danger is near, the goby fish will tap the shrimp so it hides.


This may be the most notorious form of symbiosis in that the host is always harmed in some manner. Inside or outside of the body, a parasite can be annoying, painful or deadly. Let’s talk about a few parasites so you understand what we mean.

Parasites that target humans

Fleas, ticks and mosquitoes are the most common form of parasitism. Almost everyone has been bitten by one or more of these. These critters cause an annoying itch but they also carry with them bacteria or viruses from other hosts that they have come in contact with. Diseases like dengue fever, West Nile fever and malaria are potentially deadly diseases that are what the CDC calls vector-borne. These are introduced to the host via a vector and in this case, the mosquito is the culprit.

Worms and humans

Worms are one of the most disgusting and deadly parasites and over 3 billion people are infected with at least one of what Dickson Despommier of Columbia University calls the Unholy Trinity, made up of the roundworm, the hookworm and the whipworm. While these are more common in underdeveloped countries, there are cases reported every year in Western countries, however the most prolific worm in the US, UK and Canada is the pinworm.

Relationship between organisms

  1. Cannibalism
  2. Commensalism
  3. Kleptoparasitism
  4. Mutualism
  5. Parasitism

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