Parasitoid From Outer Space

~ Dan Haynes

Since its release on June 22, 1979, Ridley Scott’s seminal genre classic Alien has had a massive ripple effect across the pop culture landscape that few movies before or since have been able to duplicate.  It’s spawned three sequels, two prequels, two spin-offs, been adapted into comic books, video games, and most recently an elaborate high school production.  It even has its own fan-centric holiday, Alien Day, on April 26th, in which fans the world over celebrate the long-running series and companies like Mondo release special Alien-themed merchandise such as art prints, t-shirts, and enamel pins.  In 2002, in recognition of its contribution to the diversity of American cinema, it was inducted into the National Film Registry at the Library of Congress alongside other classics like Beauty and the Beast, Boyz N the Hood, In the Heat of the Night, and This Is Spinal Tap.

Since Alien turned 40 years old earlier this year, I thought it might be a good time to take a look at some of the actual science behind it.  And there could be no better subject than arguably the real star of the movie, as well as the entire franchise: the xenomorph, the most perfect organism.    

A Quick Xenomorph Refresher

Before we get into the physiology of the xenomorph, let’s take a quick refresher.  While little is known about where the xenomorph comes from, what species it is, or even what gender it is, we see that it has a complex life cycle with four stages of development.  We first see it as an egg, followed by the facehugger, then the chestburster, and finally, the adult warrior. 

After the egg hatches, the facehugger emerges and leaps onto the front of Kane’s space helmet.  It secretes a type of hot, corrosive acid that allows it to break through the glass and attach itself directly onto Kane’s face.  Kane, now unconscious, is quickly brought back onboard the Nostromo with the facehugger firmly latched on and its tail wrapped around his neck.  Any effort to remove the creature causes it to wrap its tail even tighter, nearly killing its host, as well as bleed acid when cut that successfully eats through several floors of the ship’s hull, leaving only rusted metal in its wake.  After some time passes, the facehugger releases its grasp, falls off and dies.  Kane then wakes up and seemingly returns to normal.  While eating in the mess hall with the rest of the crew he first starts to cough.  Then he starts to choke.  Then he begins to suffer a series of violent and agonizing convulsions which everyone is unable to stop.  Something erupts from under the surface of his chest, splattering blood across the room and on Lambert’s face.  Finally, the chestburster emerges from Kane’s still-twitching body and quickly escapes, leaving Kane dead.  After this is the final adult warrior stage, which due to the movie’s shadowy cinematography, we only see in bits and pieces until the very end.  What we are able to make out is a massively tall humanoid creature with an exoskeleton, long spiked tail, and a second set of jaws that are only revealed when used to kill members of the crew, such as Brett and Parker.                                  

Xenomorphs of the Insect Kingdom

When it comes to organisms that are analogous to the xenomorph we have to begin with wasps.  If you ask the average person what they know about wasps, they’ll probably tell you one of a couple of things: they look like bees, they’re intimidating-looking, or they’re a nuisance during family picnics and barbecues.  One thing that might not get brought up is that they’re what are called parasitoids.  This is not to be confused with parasites, as parasites only feed off of a host organism while sometimes passing on diseases.  Parasitoids, on the other hand, feed off of and mature inside a host insect, killing it in the process.  There are several different types of parasitoid wasps, but probably the best example that bears the closest similarity to the xenomorph in terms of reproduction is the Ampulex compressa or emerald cockroach wasp, better known as the jewel wasp. 

The jewel wasp possesses a fascinating and terrifying method of reproduction with some similarities to the xenomorph.  When it’s ready to lay its eggs, a female emerald cockroach wasp will fly around in search of a cockroach.  Once it finds a cockroach it will attack it, stinging it in two separate areas, injecting it with a special type of venom that attacks two areas of the cockroach’s brain.  Instead of running away, the cockroach does nothing.  It simply remains where it is because it no longer has the willpower to do anything.  The wasp then grabs the cockroach by its antenna and brings it back to its lair, which as science writer Ed Yong memorably described in his 2014 TED Talk as “… like a person walking a dog.”  Once inside, the wasp lays an egg on the underside of the cockroach.  The cockroach is still alive, but does not struggle or try to escape because it has been rendered completely docile by the wasp’s venom.  The wasp then leaves its lair, sealing it from the outside, and flies away.  Meanwhile, the egg eventually hatches, and the larva burrows its way inside the still-living cockroach.  Over the course of the next few days, the larva grows and pupates, then digs its way out of its temporary home, leaves, and flies off to start its life cycle all over again.  Only at this point does the cockroach die.    

But cockroaches aren’t the only insect to fall prey to parasitoid wasps.  Caterpillars have also been known to become unfortunate hosts to the larvae of the Glyptapanteles wasp genus.  Like the jewel wasp, the female Glyptapanteles injects a caterpillar with up to 80 eggs using what’s called an ovipositor.  It’s a specialized organ hidden in the wasp’s stinger that is used to lay its eggs.  When the eggs hatch, the larvae feed on their host, devouring it from the inside, but avoiding inflicting any significant damage to the vital organs.  After going through several stages of development, the larvae all simultaneously chew their way out through the caterpillar over the course of an hour.  While all this is going on, the caterpillar behaves perfectly normal, only showing signs of being more bloated than normal.  After the larvae have finally emerged, the caterpillar then goes on to spin a protective cocoon around the larvae until they finish pupating into their adult forms.  The caterpillar will go on to protect the cocoon to the detriment of its own health, dying from starvation in the process, but only after the newly-grown adult wasps leave and fly away. 

And then there’s the Ichneumon wasp.  A parasitoid that was so horrific in its method of reproduction that Charles Darwin once said of them, “I cannot persuade myself that a beneficent & omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars…”  The Ichneumon wasp preys on the Alcon blue butterfly, which they find hiding inside ant colonies.  This by the way is a whole other discussion regarding insect mimicry and brood parasitism.  Once inside the ant colony, the Ichneumon will emit a pheromone that causes the ants to fight each other, giving it plenty of cover to find the caterpillar.  According to a 2008 WIRED article, “The wasp slips through the confusion, lays its eggs inside the caterpillar and leaves.  After the caterpillar turns into a chrysalis, the eggs hatch and consume the it from the inside.”    

The Jaws of Death

One of the most iconic aspects of the xenomorph are its jaws, specifically its second set of jaws.  It’s an anatomical feature that can best be seen in moray eels, which, despite their appearance, are actually a type of bony fish.  Though unlike most fish, who feed by opening their mouths and sucking in water along with any nearby prey, moray eels have little ability to generate suction.  Instead, they use what are called pharyngeal jaws, a second set of jaws hidden deep in the back of the throat, just behind the skull.  Like the xenomorph, moray eels also hunt from the shadows, hiding in their darkened homes in the holes of rocks and coral reefs.  They grab onto their prey with their main jaws, holding them in place, then the pharyngeal jaws move forward, bite onto the food, and drag it back into the esophagus after the primary set of jaws let go.  It’s a process that takes less than a second to complete, which is certainly a lot faster than it takes the xenomorph.  Although both get good marks for being exceptionally fast and efficient.

Bleeding Acid

Finally, we come to the deadliest aspect of the xenomoph’s physiology: its acid blood.  As mentioned earlier, it’s primarily a defense mechanism that prevents any tampering during the facehugger stage.  Using acid as a defensive as well as an offensive tool against predators are fairly common in various species of animals.  According to a 2012 HowStuffWorks article, “When threatened, vultures spit stomach acid and camels spit partially digested cud…Other species on Earth take projectile weapons to even crazier extremes.  Spitting cobras lob venom directly at an aggressor’s eyes…” 

Two insects that use acid as a defensive tool to great effect are the bombardier beetle and the woodland ant.  Both insects are capable of firing a chemical liquid weapon from their abdomen when threatened by predators like frogs or birds.  In the case of the bombardier beetle, it can spray a burning liquid at a temperature of 100 degrees Celsius that’s a mixture of hydrogen peroxide, hydroquinones, and the enzymes peroxidise and catalase at a rate of up to 22 mph at 368-735 pulses per second.  By limiting the sprays to such short bursts, it prevents the beetle from burning up inside.  If eaten or swallowed, it can still fire this weapon, causing it to be regurgitated.  Miraculously, according to one study, 43% of beetles survive such an ordeal.

All of this goes to show you that nature is far more fascinating or terrifying than anything Hollywood’s best screenwriters can possibly come up with.  If only more science fiction or horror movies took their cues from the insects and animals around us, we might have a richer and more interesting slate of movie monsters.       

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Sources

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Published by Dan Haynes

Curious Cinema: A Guide to Unusual Movies is a blog for moviegoers who want to learn more about the science, history, and/or mythology behind some of the greatest cult and genre movies ever made. Using both primary and secondary sources including, but not limited to, non-fiction books, articles, podcasts, and videos, I’ll inform the reader through longform posts in an easy-to-understand manner about just how close a movie’s fiction comes to reality. As they say, truth is stranger than fiction, and sometimes a lot more fascinating – and in some cases – more terrifying than anything Hollywood’s best screenwriters can come up with. New posts will be published every other week.

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