Parasitism | an introduction

The first weirdness we’re going to cover is Parasitism.

**Parasitism will be a five-part series covering various human and animal afflictions.

So, what is it? Well, for one, it’s something that pop-culture lovesFrom the Xenomorphs  in Alien, the Flood from the Halo series and the Ceti-eels of the Star Trek franchise, we are constantly bombarded by malevolent parasitic characters. Why? For the simple fact that they are creepy. 

Something that is able to burrow into your body and cause pain/control your mind/kill you is enough to make most people shudder and/or run the other way.

Before we go any further, let’s first define what parasitism is:

a non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, the host.

…thanks Wikipedia.

A couple of definitions here.

symbiotic: any organisms that live together.

non-mutual: the relationship between the two species is not necessarily beneficial to both.

Basically, a parasite is an organism (usually animal, but can also be fungal, microbial or even a plant) that lives on or in another creature (the host). In extreme cases, the parasite lives off the host, sucking the life out of it until it dies. Thankfully, this kind of bad behaviour is in the minority. Most parasites do not kill their hosts, and a lot are either completely harmless or work in your favour (you could even call these parasite-pals).

You have many parasites living on or in you right now. In fact, there are probably face mites mating on your eyelashes as you read this sentence. (!!)


© Vibhuti Patel


But, try not to dwell on that too much – there’s not much you can do about them. And indeed many animals, once infected by parasites, are pretty much doomed to either live with them – or die by them.

Parasites come in two main flavours:

Ectoparasites are parasites which live on the skin or derivatives of the skin (think head lice and fleas)

Endoparasites are parasites which live inside the host (ach!)

Parasites are thought to have evolved independently multiple times, and there has been evidence to suggest that even the mighty dinosaurs were afflicted by these little hellions. But they’re not all bad. Parasites often act to drive the evolution of host species, because natural selection is constantly working to develop adaptations for defence. The parasite is also constantly evolving as a response, creating a kind of evolutionary arms race. These evolutionary traits of parasite and host alike can have effects which trickle down into other aspects of the ecosystem. In this way, parasites have the capacity to alter entire ecological communities. Many parasites are also utilised in medicine to great effect.

So, it looks like parasites are not necessarily the villains they’re made out to be. Of course, this may be part of their master plan…

…dun dun dun.


Featured image is credit of David Hughes, sourced from:


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