Alien Entomology: Science on the Silver Screen

It can be difficult to keep up with the breakneck pace of scientific advancement these days, even if you work in a museum’s science department. For the most part, these advancements are for the better. However, some are tougher to love and are met with resistance. The opinions that drive people to love or hate different aspects of science are influenced by a variety of sources. For better or worse, one of those sources is popular media, like films.

Most movies are not made with education in mind and the science they portray is rarely unbiased. Would people feel less uneasy about artificial intelligence if they hadn’t seen the Terminator or the Matrix?

I love science fiction films of all levels of quality and don’t think we need to ban movies about genetically engineered sharks, but I do think it’s important to be able to examine the portrayal of science in film critically. This was one of the major goals behind the Bruce Museum’s summer film series, Science on the Silver Screen. We watched four science fiction movies throughout the summer. Each film was paired with a special guest scientist, there to explain whether the science was more fact or fiction.

The audience discussions with these experts were wide-ranging and fascinating. The most recent film we watched this way was Alien, and it has given me an all new appreciation for this sci-fi horror franchise.

Be aware: The subject of this article is Alien and the real-world equivalents of the xenomorph monster. The lifecycle of the alien is rather horrific, and some of the living creatures discussed will be equally unsettling.


Our expert for Alien was Dr. Matt Frye. Dr. Frye is an entomologist, a scientist who studies insects. The alien xenomorphs might be from another planet, but they have a very insect-like lifecycle and many insect-like body features as well. They are also something else that Dr. Frye has experience with: Parasitoids.

Both parasites and parasitoids derive nutrients from a host organism at the host’s expense, but other aspects of their biology differ profoundly. A parasite is generally much smaller than its host and doesn’t cause its host’s death, at least not immediately. Sometimes a parasite will move from one host to another in search of more favorable conditions. Humans have a lot of parasites, ranging from head lice to tapeworms.

Fortunately, humans don’t have parasitoids. Parasitoids are much larger in comparison to their host, tend to stick with a single host throughout their life, and their effects are much more dire. Parasitoids almost always kill their host, and when they don’t, the host is left infertile or otherwise impaired. The xenomorph is certainly a parasitoid, as its emergence causes certain death in the host without immediate intervention. 

Xenomorph lifecycle

The xenomorph has an infamously gruesome lifecycle. There is one breeding queen for each xenomorph hive. The queen lays the eggs, which lay dormant until they sense movement nearby. At that point, the eggs hatch into the skittering “facehuggers,” which attach to the face of their hapless host and inject a xenomorph embryo into the host’s body cavity. When the infant alien has achieved maturation, it violently bursts from the body of its host, a process that is immediately fatal in almost all cases. Then, over the course of mere hours, it grows from cat-sized to human-sized, ready to cause mayhem.

This lifecycle might seem rather far-fetched, but Dr. Frye’s presentation made it clear that it is far more realistic than expected. While there is no insect that behaves exactly like a xenomorph, there are many that come frightfully close.

If you want to see a scene of sci-fi horror, you may want to start with exploring your own back yard…

(The following information is adapted from Dr. Frye’s presentation and includes spoilers for the Alien film.)

Eggs: Dormant, Activated by Movement

In Alien, the protagonists come across hundreds of alien eggs in the cargo hold of a derelict spacecraft. These eggs have been abandoned for years, but one stirs into life when a human walks by, unleashing its fiendish inhabitant upon the unlucky officer.

Many people have personal experience with an insect that has an analog to this behavior: Fleas.

It isn’t the flea eggs that lie dormant, but their cocoons, or pupae. Flea eggs hatch into immature larvae. After another week or two, the larvae weave a cocoon around themselves, inside which they are changing into their adult form. Under ideal conditions, a flea might spend only a couple weeks in its cocoon. When the situation is less favorable, the cocoons fall dormant. They remain in dormancy until they sense movement or heat, signs that a potential host is nearby. It is only then that they emerge.

This is one of the reasons why it is so difficult to eliminate a flea infestation once they’ve started breeding. Even if you kill all the adult fleas, there may be cocooned fleas lurking about for as long as six months, waiting for the perfect moment to pop out and stop biting again.

Facehugger: Mobile, host-finding

When the xenomorph egg hatches it is a facehugger that comes out. While in the facehugger stage, a xenomorph has only one goal: Find a host. They skitter around on their eight eerie legs, actively pursuing their targets. They anchor themselves to a host by wrapping their tail around the host’s neck, seize onto the head with their legs, and insert a long tube down the host’s throat, depositing a xenomorph larva within them. The human is alive, though unconscious, during this process, making it perhaps the most horrific part of the xenomorph lifestyle. That is, until the next stage occurs.

This mobile host-finding behavior is seen in a number of insect species. Instead of “facehugger,” the mobile parasite stage of these insects is called a planidium (plural: planidia). The Strepsiptera, or “twisted-wing parasites,” are one such group of insects. They look a lot like flies as adults, but their adult form is short-lived. They may survive for as little as five hours, only living long enough to breed.  

In some Strepsiptera species, the eggs hatch within the female. The larvae eat their mother from the inside out. When they emerge, they swiftly try to find a new insect host before starvation sets in. When they find a target, they climb onto the insect and secrete enzymes to soften its protective exoskeleton. When it is properly weakened, they burrow their way inside. The living host is both their food and shelter, much like growing xenomorph larvae are sheltered and nurtured by a living human body. When the planidia begin to reach maturation, well, that’s where the next part of the xenomorph lifecycle comes in.

Chestburster: Immature Stage

Like its name implies, the chestburster stage of the xenomorph is known for messily bursting out of a human chest, which is shown on screen at least once per Alien franchise film. It is very similar in appearance to an adult xenomorph, though often has underdeveloped limbs and a more serpentine form. As it turns out, “bursting” from a host is a very effective life strategy for many in the insect world.

Though insects with planidium stages seek out hosts on their own, adults do the work in other species. There are a number of wasp species that puncture other insects and lay eggs directly inside their bodies. The eggs hatch into larvae that slowly consume the host while developing within them.

At some point, the larvae will have matured enough that it’s time to move on to the next stage: Cocooning. Cocooning can take place either inside the host or outside. Those that cocoon outside the host do their “bursting” while still in larval stage. Those that cocoon within a host burst out after metamorphosing to adult form, creating an exceptionally alien-like scene.

Parasitic wasps are incredibly common and incredibly diverse, with as many as 100,000 species of wasp employing this lifestyle. Should they all be flushed out air locks, like so often happens with their xenomorph brethren?

Wasp cocoons on a tomato hornworm. Image by Max Wahrhaftig

Wasp cocoons on a tomato hornworm. Image by Max Wahrhaftig

Absolutely not! They don’t prey on humans, only other arthropods. This makes them excellent for pest control. There have been over a 1000 intentional introductions of parasitic wasps to agricultural areas. It’s normally a bad idea to introduce a non-native species to a new area, but these wasps are a force for good as long as you aren’t a caterpillar.

If you ever see a hornworm in your garden with white cocoons stuck to its body, leave it alone. The hornworm is covered in parasitoid moth cocoons, which will someday emerge to prey on more hornworms and help keep your garden safe.

A tarantula hawk dragging a paralyzed tarantula.

A tarantula hawk dragging a paralyzed tarantula.

Adult Alien:  Big, bad, and social

Adult aliens are monsters of predatory efficiency. Their destructive capability is so great that they are sometimes called “perfect organisms” by their more introspective prey. There are a number of insects that are probably as scary as a xenomorph to something closer to their size. The tarantula hawk is one of them, a spider wasp that specializes in hunting tarantulas. They have the sleek black look of an alien predator and one of the most painful stings ever recorded. They grasp tarantulas with their claws, positioning themselves for a sting. Once the tarantula is paralyzed by the wasp’s venom, the tarantula hawk drags it to her nest, where she’ll lay an egg on the abdomen of the spider. When the egg hatches, the larva burrows into the still-living spider.

Another interesting facet of xenomorph behavior is their tendency to form hives. This is straight out of insect biology. Like the xenomorph, many species of ants, termites, bees, and wasps form hives where a single female breeds and the rest of the population carry out various roles. In an ant colony, the workers are in charge of everything from foraging to taking care of young. Until the films show more of the inner workings of a xenomorph hive, the finer details of their social behavior remain unknown.

Acid blood

The xenomorph, fierce enough already, has another line of defense: Molecular acid for blood. When injured, its blood can spray onto its attacker and cause life-threatening damage within a matter of seconds. The acid blood can also eat through the metal of spaceship hulls, making defeating it a complicated manner indeed. I’m relieved to report that there are no Earthly organisms with acid for blood, but there are some insects that have a similar idea.

Image by skymeadowsstatepark

Image by skymeadowsstatepark

The main purpose of a xenomorph’s acid blood appears to be defense. Many characters in the film hesitate to attack the xenomorph after they discover this feature. The beloved monarch butterfly has a comparable, though toned down, deterrent against attack. Monarch butterfly caterpillars feed on milkweed and incorporate the plant’s toxic chemicals into their body.

A bird that eats a monarch caterpillar or butterfly will feel ill afterwards, leading it to avoid eating them in the future. A monarch butterfly might not spray you with acid if you attack it, but it does have internal chemical defenses that protect it from harm.

Other thoughts

Dr. Frye touched on a number of other subjects in his Alien discussion. One xenomorph feature he simply couldn’t explain was their swift growth rate. It’s implausible enough that an alien could grow so large so quickly, but that growth rate appears even more ridiculous when you take into account that the xenomorph isn’t ever shown eating anything. It attacks and kills humans, but it never appears to linger around to ingest any part of its kills, and there is no evidence that it came back and did so later. The large amount of fluid that drips off the alien is rather puzzling too, as the alien is likewise never shown to drink.

Dr. Frye gave all of us a lot to think about that day, and hopefully this translation of his presentation will give blog readers something to chew on too. We would like to run this event series again next year, and if we do, I hope to see you there!

What movie are you most curious about the science of?

- Kate Dzikiewicz, Paul Griswold Howes Fellow

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