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Is Xenomorph XX121 the scariest biological weapon ever created or the most efficient hunter that ever evolved? There is no definitive answer, but everyone agrees that if you encounter them, you probably won't live to talk about it. An invasion of xenomorphs can mean extinction for every other species in their vicinity. Fortunately, fans' understanding of Xenomorph XX121 has grown substantially since its introduction in "Alien" (1979).

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Since 1979, Xenomorph XX121 has appeared in movies, books, comics, and toys. Each new chapter in the xenomorph story gives audiences new reasons to fear them. The list of their hunting capabilities is a long one but they also have a handful of weaknesses someone might use to survive against the so-called perfect organism.

Updated by Matthew Z. Wood on 9/9/2022: The Alien franchise has changed a lot over time, as has CBR. To better serve our readers, this updated list catalogs the xenomorph's strengths and weaknesses in a more organized format.

The Xenomorph's Biggest Strengths

Xenomorph Eggs Can Wait A Long Time For A Host

Ovomorph alien egg preparing to release facehugger

Don't be fooled by the xenomorph egg's innocuous appearance. Also known as the ovomorph, it protects the facehugger parasite inside itself while they both wait for a suitable host to stumble by. When a suitable host comes close enough, the egg opens and the facehugger latches onto its host.

Ovomorphs are hardy, long-lived creatures. They're able to survive for as long as hundreds or thousands of years, while they wait for a prospective host to stumble within range. The eggs have been known to grow roots that draw nutrients out of their environment. Their outer layer is extremely strong and can survive significant physical trauma. They have a rudimentary nervous system, and when cut, spurt out powerful acid as a defense mechanism.

Almost Any Species Can Serve As A Host For Xenomorphs

Alien queens organizing troops

Ovomorphs and facehuggers aren't picky. Any animal that's large enough for a facehugger to force an embryo into can be a host. Using almost any host organism means xenomorphs can start colonies almost anywhere. Intestingly, the xenomorph experiences some genetic drift as it forms in its host body, and grows to resemble its host, helping it adapt to its new environment.

While the human variant is the most well-known, but the Predalien from Aliens vs Predator: Requiem (2007) is perhaps the nastiest xenomorph anyone's encountered. They mirror their Predator host's humanoid body, "dreadlocks" and mandibles, but are even stronger. This variant skips the facehugger phase entirely and can force an embryo into a host via its mandibles.

Acid Blood Is A Terrifying Defense

Alien acid blood

Xenomorph blood provides them with the perfect defense from teeth, claws, knives, and any other melee weapons. Their blood is a powerful acid, so injuring a xenomorph almost always destroys its assailant and can eat through metal and deep into natural surroundings. This chemical defense is present throughout every xenomorph's life cycle.

Theoretically, there might be more to a xenomorph's blood than just an internal weapon. It may function like battery acid and facilitate a high-energy chemical process within their bodies. Xenomorphs rarely feed on their victims, so they may be powered entirely by potent internal energy supplies.

Xenomorphs Can Lie Dormant, Without Movement

A hiding xenomorph from Alien:Covenant

Patience is a virtue that the xenomorph knows well. Like the ovomorphs, an adult xenomorph can wait a long time for victims. They have the ability to enter a dormant state with absolutely no movement. They do not breathe, so there are no subtle body movements to warn their prey. With a black carapace, they can usually blend into any shadows and wait for prey to come to them.

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This comes in especially handy in xenomorph hives and other locations where they have begun building their home. The xenomorph's black exterior provides camouflage in the resin-based structures they build along all walls and floors. This makes them efficient ambush predators and exceedingly difficult prey.

Xenomorph Senses Are Perfectly Calibrated For The Hunt

Paul Church, a Xenomorph xx121 expert, in the Dark Horse Alien comics

Most of the research surrounding the physical characteristics of the xenomorph XX121 comes courtesy of Lasalle Bionational, a multinational conglomerate from the world of the Aliens. Their research was published in "Aliens" magazine, Vol. 2 #11 by Dark Horse International in 1993. Aliens originally republished several comic runs set in the world of "Aliens" for U.K. readers. These were printed in the U.S. by Dark Horse as individual comics. Volume 2 of Aliens expanded coverage to include supplemental materials.

Lasalle Bionational uncovered three different senses that xenomorphs can use to find prey. They have delicate vibration-sensitive organs along the sides their heads. Their thermosensitive organs are at the front of their skulls, letting them detect body heat. Finally, their vestigial eyes have very limited functionality but may allow them to sense each other. Dr. Paul Church, introduced in Aliens: Labyrinth (1993-1994, Dark Horse Comics), found an organ that allowed xenomorphs to sense electromagnetic fields in the brains of potential victims as well.

Xenomorphs Work Together As A Pack

Alien xenomorphs face off against Colonial Marines in Aliens

Xenomorph XX121 is a social monster. They work together to both capture and herd prey. Their methods of communication are unknown, although Lasalle Bionational hypothesized that it could be through pheromones and non-audible queues. The xenomorphs do make hissing sounds and loud blood-curdling screeches but that doesn't seem to be for communication. It is possible that the noises they make are related to echolocation.

Xenomorphs are able to communicate enough to not only coordinate attacks but also solve problems. During the movie Alien: Resurrection (1997), two xenomorphs killed a third and used its acidic blood to escape their confinement. In the special edition home video release of Aliens (1986), the xenomorphs were able to redirect their efforts when obvious routes of attack were blocked and work around automatic sentry guns by climbing into the ceiling.

Xenomorph Exoskeletons Let Them Live Anywhere

Queen Xenomorph bares its teeth

One characteristic that almost all variations of xenomorph XX121 share is a protein-polysaccharide exterior. This sort of exoskeleton is composed of chitin in nature and xenomorph shells can withstand a lot of damage. However, their hard chitinous exterior is only part of the power of their exoskeleton. They also replace their exterior cells with polarized silicon, giving them resistance to adverse environmental conditions. Essentially, they can live almost anywhere.

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Xenomorphs are so tough that defeating them requires heavy weaponry or equipment, often fired at point-blank range. Small arms do little to them and the best way to fight them is with massive explosions triggered from a long distance. This requires resources and planning, making xenomorphs truly deadly foes.

Xenomorphs Are Smart Enough To Solve Mechanical Problems

A xenomorph from Aliens: Dark Descent

Vicious monsters are bad but vicious monsters who can open doors are a lot worse. Xenomorphs have shown the capacity to learn thow to use simple mechanisms by observing their prey. The host organism that birthed them might have some impact on how this intelligence develops, and it might require lifeforms with a higher capacity for intelligence, but xenomorphs can use rudimentary tools.

There are chilling examples of this in the movies. In Aliens, the xenomorphs were able to cut the power to the part of the base where the humans were hiding. In the same film, the Queen was able to use an elevator after watching Ripley enter one and escape to the top level. In Alien vs Predator and Alien: Resurrection, the xenomorphs used their acidic blood to free the Queen and escape confinement, respectively.

Xenomorphs' Second Jaw Is A Surprising Weapon

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Xenomorph XX121 has two sets of jaws. The first set of jaws is of limited use, possibly used for intimidation or to protect the relatively fragile inner jaw. The inner jaw, however, can be launched out of the xenomorph's mouth with tremendous speed and force and it can smash through animals' skulls and into their brains in an attack known as a "headbite."

Aliens climatic scene provides a terrifying example of how a xenomorph can use its inner jaw. Armed with a power loader, Ellen Ripley was relatively well-matched against the Queen. However, the Queen briefly immobilized her and attempted multiple headbites, rapidly retracting its inner jaw after every strike, and trying multiple angles as it tried to incapacitate her.

Xenomorphs' Blade-Tipped Tail Is Their Impaling Weapon

A Predator impaled by a xenomorph, from the AvP film franchise

Xenomorph XX121 is also known for its segmented, blade-tipped tail. The tail's shape seems to vary across xenomorphs, possibly because of variations in hosts. However, in all cases, the tail exhibits great strength and can be used as a bludgeon or a spear. It has enough strength to pierce through and lift large prey. Xenomorphs can also use their tails to push attackers away or clear obstacles.

The tail is frequently used in ambush attacks. Over the course of the Aliens franchise, the creatures have used their tails to attack humans, Yautja (aka Predators), and very nearly destroy the synthetic humanoid named Bishop as well.

Xenomorphs Learn Genetically

Dr Wren and an alien Xenomorph from Alien: Resurrection

One of the odder abilities xenomorphs exhibit is the power to inherit memories, both from previous generations of xenomorphs and from hosts. In Alien: Resurrection, when Ellen Ripley is cloned, xenomorphs derived from her clone all share her specific memories.

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The film's antagonist, Dr. Wren, speculates that their genetic memory is designed to maintain cohesion among the species. The potential downside of a xenomorph embryo's genetic drift is a loss of xenomorph identity in favor of its host's identity. This could create life-threatening confusion. Genetic memories ensure that the new xenomorph will know what it is and how to live, without confusion from the host.

The Xenomorph's Biggest Weaknesses

Xenomorphs Depend On Hosts For Adaptation

Ellen Ripley faces a xenomorph Queen

Xenomorphs have more strengths than weaknesses but it is possible for potential victims to exploit their limitations. One of the xenomorphs' less likely weaknesses is embedded in the way it adapts to its environment according to its host. This means that some xenomorphs are better suited to a given locale than others.

Changing locations can make a difference with these hyper-adapted predators. A xenomorph birthed by a fast runner, like a cheetah, could be tripped up by twists and turns or could easily overheat. Similarly, xenomorphs birthed by tremendous hosts couldn't fit into small spaces. Exploiting these limitations is key and is probably what kept Newt alive in her colony in Aliens.

Xenomorphs Are Smart But Not Too Smart

A xenomorph from Aliens

Xenomorphs are intelligent and can learn, but not as quickly or as well as people. Multiple multinationals have been able to keep xenomorph subjects contained for study in laboratory settings. This usually ends badly, of course, but in the past their escapes have been facilitated by human negligence, arrogance, or both.

Xenomorphs' problem-solving capabilities are limited to their immediate needs, so it is possible to trick them. This can allow quick thinkers to distract them or lure them into traps or kill zones, like the sentry guns in Aliens. The xenomorphs place almost no value on individuals, except for a Queen or Empress, so a well-placed trap can thin their numbers and give survivors a fighting chance to make it to safety.

Xenomorphs Hate Extreme Heat And Cold

Ripley burning the xenomorph eggs in Aliens

Xenomorphs do share most lifeforms' aversion to fire and baking them in their carapace is one of the few ways to injure them without releasing their acidic blood. While stronger variants like Queens and Predaliens can handle at least some fire, most warriors and drones cannot. This makes flamethrowers one of the best weapons against xenomorphs, both for killing them and keeping them at a distance.

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Xenomorphs also have trouble with rapidly changing temperatures. The molten lead in Alien 3 may have been enough to kill a xenomorph on its own, but the cold water from the sprinklers shattered its superheated exoskeleton. The extreme cold of outer space also seems capable of killing them, if not immediately. Xenomorphs don't appear to breath, and seem drawn to spaceships, so this is an important point.

Xenomorphs Keep Their Victims Alive, When Possible

Dallas cocooned by the xenomorph in Alien

Xenomorphs don't eat their prey but instead collect them for impregnation. This can take some time since the xenomorphs temporarily cocoon their prey and deposit ovomorphs nearby. Once they're ready, they hatch out a facehugger but this provides a window of opportunity for escape or rescue.

While most xenomorph victims still die terribly, Ellen Ripley was able to rescue Newt when she was captured in Aliens. By keeping a cool head, she was able to position herself close enough to hear Newt's screams for help and kill the facehugger before it attached itself to her. Ripley is the xenomorphs' most successful foe, so her example is always worth learning from.

Xenomorphs Can Be Stunned By Vibrations

A soldier firing a sound cannon in Dark Horse's Alien comics

After so much human slaughter at the hands of xenomorph XX121, humans needed some leverage. Lasalle Bionational's discovery of the xenomorph ability to sense vibration along the sides of their large heads gave humananity a potential advantage. In an emergency, ultrasound vibrations can stun xenomorphs and buy time for an escape.

Z.C.T. Corporation was able to weaponize this idea. The Aliens: Rogue comics featured a sound cannon created by Dr. Ernst Kleist. The sound cannon fired a directional burst of ultrasound pulses to overload the xenomorph's senses. Unfortunately, the cannons were unstable and had a tendency to explode. However, weaponizing sound is still a possibility, and this also implies that explosions and other loud noises might be used to cover human movements or even blind xenomorphs.

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