A tapeworm living in the human gut has no digestive system of its own. It absorbs the intestine's processed nutrients directly through its outer surface, like a ready-made all-over- body-meal. So the tapeworm is exploiting its host's digestive system instead of investing in one of its own. It siphons off the goodness from its human benefactor - who goes to so much effort (earning a living, shopping and eating) to get the food down there in the first place - and uses it for its own sustenance.
The case of the tapeworm makes us think about what it is to be a complete organism. While we may be used to the idea that humans have some other organisms (like gut bacteria) acting as internal helpers, we may tend to think that they are not really essential, but we just tolerate them because it suits us, like the crocodile allowing the bird to pick its teeth because it can't be bothered evolving - or inventing - a toothpick of its own.
We tend to feel that we are not actually dependent on the parasite, in the way that the parasite seems dependent on us. After all, our gut provides the parasite's very home - a nice place to settle down, hatch eggs and bring up the larvae. Without 'us', there can be no 'them'. In a sense we live and breathe on their behalf. The dependency is clear in cases like the tapeworm, which we might regard as an incomplete organism - one lacking a digestive system - whereas we consider ourselves whole, even though our own digestive system makes use of live-in non-humans to help it function.
This interdependency means that humans might be regarded as 'composite' creatures by any objective observers. An alien taxonomist studying life-forms on Earth might classify us not as a distinct species, but as a composite life-form comprising not-quite-whole species of tapeworms, microbes, and homo sapiens.
Conversely, we might face difficulty in recognising distinct alien species, if they too formed a tangled jungle of taxons and taxonomists, hosts and parasites. And once we are used to ourselves as hosting parasites - like aliens within us - we can also imagine having alien parasites living off us too.
Imagine a cold-blooded alien that came to live on or in our bodies because of our warmth. Such a parasite would have no central-heating system of its own, but simply live off our body heat. All its other functions, like eating, sleeping and reproduction, it could take care of by itself.
Once it had made itself at home, it might then tap into some of the other local facilities. Imagine that the parasite could plug into the visual system of its human host. Instead of the parasite as a wretched 'bug' blindly groping around the murky bowels of its host, we could imagine this parasite perched just behind our eyes - like our own 'mind's eye' perspective - taking in the view by tapping into our optic nerve, like live video streaming. It would be able to sense all the visual richness available to the human eye, even if it had only the intellect of an insect to process the information.
Or, imagine a parasite that not only connected to the optic nerve, but plugged directly into the brain. Residing somewhere in the skull, it would not need a brain (or cranium) of its own, but could feed off the thoughts and mental processes of its host. It would have access to all the sensory information processed by the brain, and all our memory archives too.
And if there were a two-way data feed, the parasite's body might even be able to send its own requests to the brain's central processing unit, perhaps while the brain was otherwise idling. Perhaps indeed our brainless alien parasite could plug in, tune in and switch on the brain, and ask it to do a few calculations, or run a few scenarios, while we slept.
Like a 'virus' in the brain, such an alien parasite would be metaphorically feeding off our brains - rather than literally feeding off our stomachs - while happily carrying out its other bodily functions for its own benefit.
But if it is spooky to think of an alien body tapping into our brain, then how about an alien that brings its own brain, but takes over our body? It could unplug our brain, and use our body to breathe Earth air, to eat Earth food, and generally see the sights. That would be not so much a parasitic alien brain-sucker, as an invasive alien body-snatcher.
The advertisements that appear on paper and online versions of The Alien Times do not necessarily represent the views of the Alien Times. The Alien Times takes no responsibility for any transactions that occur between advertisers and readers.
The authors of articles that appear in Alien Times reserve the right to copyright their work. Please DO NOT copy any articles that appear in Alien Times without first receiving permission from the author of the article (when known) or the Alien Times Editor.