The genius of the Alien movies is the creature ticked all the boxes of things we find horrible. As well as a bad attitude, it had slithery skin, vicious claws, an excess of large pointy teeth, and dripping saliva.
That's bad enough, but then we discover it's not just a predator: it's also a parasite.
I'm not aware of any real animal that is both, but if you do, please let me know.
A predator, we can both fear and admire - they are, after all, a bit like us. We tell epic stories of bold hunters who tracked down and killed their prey.
A parasite, on the other hand, triggers revulsion. The key difference, of course, is that a predator consumes its victim after it's dead, while a parasite eats it alive.
While it's a bit much to ask for you to love a tapeworm, you'd probably enjoy the tasty "bush tucker" yellow berries from the Australian native mistletoe.
An even better reason is that, as with every other branch of life, parasites are an integral part of the environment. The web of life has evolved with parasites where they have crucial roles such as propagating species or as a source of food.
A so-called ecosystem service where nature does the work for us for free, is controlling pest species. It's estimated that this is worth billions of dollars in value.
Unfortunately parasites have a PR problem and are seriously under-represented in scientific research.
The great majority of work done is with the goal, not of understanding their place in ecosystems, but of how to kill them.
In one review of biology textbooks, about three quarters did not even mention parasites.
They are a diverse group, encompassing bacteria, fungi, viruses and protozoans.
It's thought that nearly every species on the planet has co-evolved with at least one parasite. There may be as many as 300,000 different types of worm that parasatise vertebrates. They can inhabit just about every organ of every species on every continent.
Some are extremely specialised, with a life cycle involving as many as five different hosts.
This can make them vulnerable to extinction when a host organism is also under threat.
Aside from the significance of parasites themselves, this story points to the fact that every species in its proper place is part of the deeply interconnected whole we call an ecosystem.
While it's easy to be captivated by the need to preserve a creature with a cute face and soft fur, even the lowliest bacteria, fungus or parasite makes it complete.
Or, to misquote John Donne:
No species is an island,
Entire of itself.
Each is a piece of the continent,
A part of the main.
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