What Is Parasitism?

Category: Feeding Behavior.

The word parasite sends most people into a tailspin. Parasitism is a relationship between two organisms where one benefits at the others expense. Parasites can live in or on the body of the host. Parasitism can be harmful to the host, sometimes they can be fatal.

Adult Taenia saginata tapeworm. © CDC.

Our worst nightmare: tapeworms

A parasite that humans fear most is the tapeworm. This is a segmented flatworm that can attach itself to the insides of animals. Not only does it attach itself to animals, but it can also attach to a human intestinal wall. They are very dangerous because they deprive their host of nutrients by consuming their partially digested food.

Ectoparasites: a male human head louse. © Gilles San Martin.

Ticks and fleas

Fleas and ticks are also a danger to their host because they bite and suck the blood, and they also spread disease. Humans are also not immune to these parasites. The itching from flea bites can be very annoying. The oceanic equivalent of a flea is the barnacle. While they don’t seriously harm their host, the whale, they do cause an itch which can be unbearable.

Acrodactyla quadrisculpta larvae living on the back of Tetragnatha montana spider. © Jeremy A Miller.

Types of parasitism

Parasites can have several possible outcomes. One of them is commensalism, this is where they co-habitat without causing harm. The second is mutualism, this is then they co-habitat in a non-lethal manner and both benefit. The third is true parasitism where the host is actually sickened by the relationship. One version of true parasitism is by stealing either food or nesting items and it is called kleptoparasitism.

That is why you need to cook your meat

The reason that cooking animal flesh has to be done with care is that all animals play host to some form of parasite at some point in their life cycle. Eating raw meat, fish or poultry is always a gamble.

Epiparasite or hyperparatism: Adult Emerald Cockroach Wasp would sting a cockroach and use it as a host for its larvae. © Muhammad Mahdi Karim.

Varieties of parasitism

  1. Endoparasites: live inside the body of the host, i.e. the pinworm that lives inside the animals stomach.
  2. Ectoparasites: live outside the body of the host, i.e. the flea, the tick, the tsetse fly and lice.
  3. Epiparasite: feeds on other parasites, i.e. the fly larvae that lives in the wasp larvae that lives on the wood-boring beetle larvae.

Many parasites enter their hosts through vectors

Malaria, for instance, is considered a parasitic organism and is most often introduced to its host by its vector, the mosquito. There are also parasitism in the plant kingdom. The fern and the orchid are prime examples of this. It also includes many varieties of moss and lichen.

They are rapid reproducers

Parasites are smaller than their hosts and most often they are rapid reproducers. They don’t have to search for the basics of living so that they can spend all of their time propagating their species. This is how the host gets ill from their presence, one or two can be overlooked but entire villages of parasites can kill a host. The parasites aim is not to kill its host, as it relies on the host for everything it needs to survive, but it doesn’t often work out that way.

Some relationships are complicated

There are instances where the parasite and the host evolve together. Parasites of this caliber are adaptive, they use the hosts in ways that harm it. There are also parasites that have caused the host to have a symbiotic relationship with another species. In the ocean, remoras swim with and attach to whale sharks, then they eat the parasites in exchange for being protected. The ladybugs live on plants and eat the parasitic aphids, they get food in exchange for cleaning away the potentially plant-killing little beasts.

Parasites are one of the worst relationships for the host

Oftentimes, in humans, parasitism can lead to serious injury of organs and eventually if left unchecked, it will lead to death. The parasite doesn’t want to kill its host but because they breed so prolifically it can’t be helped. This is especially true of the parasites that rob the host of nutritional substances.

Relationship between organisms

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

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