In the realms of the sci-fi genre, writers, filmmakers, and audiences have been fascinated with the idea of beings beyond the stars. How many times have we thought about what it might be like to communicate with a race of creatures from a planet unlike our own? How often have we imagined making contact with some race of people millions of lightyears away? It's an admirable notion, but what if these interstellar beings weren't exactly warm in the reception department? What if they saw not to communicate, but to conquer? What if they see the race of earthlings not as brethren, but as insects, slaves, or food?

The world of the silver screen has had no shortage of these terrors from outer space. From the kitschy B-movies of the '60s to the body-horror fueled nightmares of H.R. Giger,  we've seen more than our fair share of alien adversaries. They've come for our planet, they've come for our enslavement, and they've come to suck out our brains, but we've not stopped loving them yet. There are legions of galactic goons out there that have tried to stick it to us, but we keep coming back to take them out again and again. These creeps and creatures prove that the life outside our planet might be intelligent, but that doesn't make it friendly. Here are twenty of cinema's most dangerous aliens.

20 THE THING FROM ANOTHER WORLD

Though not as popular as its remake from John Carpenter, The Thing From Another World was at one time one of the most chilling films of the '60s. With its isolated setting, an intelligent crew of scientists, and one rapidly evolving alien, it set the framework for many creature-features to come. It's considered a cult film by today's standards, and we can't leave it off the list.

Like many films of its time, it was a warning against the threat of a nuclear war. The idea of an enemy with better technology had many watching the skies. Though the effects are cheesy and the monster laughable, the terror between the lines was all too real.

19 RATHTARS

For those not familiar with the new Star-Wars trilogy, Rathtars are basically every Lovecraft monster rolled into one. They're literally balls of eyes, tentacles, and teeth, and they are one tough customer. When they make their appearance in Episode VII, we can't help but admire how ridiculous and deadly these guys are.

We don't know how Han Solo got them, we don't know why he's hauling them, but we do know it'd make for an interesting story. After being caught by two gangs of bounty hunters, Finn and Rey release them to make their escape, and the results are quite messy indeed. The hunters are devoured and our heroes flee. Some might argue that they're just substitutes for the Rancor, but tell that to Kanjaklub.

18 MARTIANS (WAR OF THE WORLDS)

H.G. Wells created them, Orson Welles gave them a voice, but the silver screen brought their doom and destruction to life. The sci-fi genre has plenty of aliens invading Earth, but these are the pioneers of the business. The image of a spaceship crash-landing on Earth and bringing with it untold chaos all harkens back to this classic.

Both the 1953 adaptation and the 2004 remake have their own take on the menacing Martians that come to Earth. The original had its gooey-looking puppets and the remake had its standard Speilberg fare, but both had plans for the destruction of Earth. Their tripods, war machines, and death rays certainly made mincemeat of the humans they terrorize.

17 THE BLOB

Yet another classic creature-feature, this slimy, sticky, slice of space jam is one tough customer. Though its appearance resembles that of a giant Jell-O mold, it lacks the sweetness and soft spot. The Blob is an eating machine, able to ensnare and devour human prey in an instant, not even leaving a crumb.

The Blob gets its edge by a single drive, hunger. It has no face, no logic, no mercy. It continues to eat and expand. It's like a rabid animal that can't be contained. Had the protagonists of the films not figured a way to stop it, it could have completely ingested the world. It goes to show, you don't need a death-ray to be a hostile invader.

16 AUDREY II

He's just a big green mother from outer space and he is bad! This soul-singing botanical baddie is hungry for human flesh and will bust out into a big musical number to try and get it. What started out as a seemingly harmless little plant in Mr. Mushnik's flower shop soon turned into a big problem when he starred in Little Shop of Horrors.

Take it from us, don't feed the plant. Based on the '60s horror film of the same name, the musical features a plant-based bad guy with an insatiable appetite and a jazzy set of pipes. The mutant plant from another planet wants to grow and grab the world by his vines, eating whatever gets in his way.

15 BLUE ALIENS

Some aliens try to eat us, some just want to enslave us. One of the most beloved '80s horror flicks, They Live! is equal parts horror-comedy and social commentary. With Rowdy Roddy Piper and Keith David squaring off a hidden race of blue terrors, there's bound to be some sparks flying.

Armed with a shotgun, and a pair of reality-clearing shades, John Nada goes toe-to-toe with an evil empire who rule in tandem with the Earth's upper class. Instead of technological warfare, these aliens use subliminal messaging to keep their prey docile as they rule the planet. The sunglasses show the monsters hiding in plain sight, and our hero has to come in and kick major butt after he runs out of bubblegum of course.

14 THE BODY SNATCHERS/POD PEOPLE

One of the most interpreted stories in the realm of science fiction,  Invasion of the Body Snatchers is yet another tale of an alien enemy hiding in plain sight. When alien spores land on Earth, people disappear and are replaced by pod-grown doppelgangers as the creatures slowly attempt to take over the world. The creatures themselves aren't visually scary, but the fact that they could be anyone is chilling.

Where The Thing was an allegory for nuclear war, Invasion of the Body Snatchers held symbols of a communist threat living amongst us in the states. Inspired by the red-scare of the '50s,  the film uses paranoia to get its scares more from what the audience doesn't see. Who knew foam and plant pods could be so scary?

13 ROMULANS

Star-Trek is full of different aliens, creatures, and beings spread across the universe. It's impressive to see such a melting pot of different cultures, but this collective of personalities isn't without its aggressive or hostile members. The Romulans are no stranger to trouble for the Galactic Federation, and Star Fleet has certainly had their share of encounters.

Genetically similar to the Vulcans, the Romulans are a power hungry and often xenophobic race of pointy-eared beings. They admire war and political power where their Vulcan counterparts regard intelligence and calculation. They can also be vicious warriors even going as far as to bend time to destroy a rival planet. Forget live long and prosper, these guys are command and conquer.

12 KLINGONS

Klingon-death-scream-(1)

Of course, we can't leave without talking about the warmongering Klingons. One of the most feared races in the galaxy, the Klingons are a mighty force steeped in tradition and bloodshed, which makes them one of the more aggressive species on our list. Some are more benign, but many of this barbarian-like race have caused more than a few scraps for the Star-Fleet crew.

The Klingon Empire boasts powerful warships, heightened skills in battle, and an outright more intimidating in their culture and appearance. Taking attributes from the Soviet Union and also feudalist Japan, their affinity for battle and sacred tradition earn them a spot on our list. Cunning and somewhat savage, the Klingons will always be a fearsome face in outer space.

11 BUGS

Who says you need to be complex and gritty to be a good sci-fi film? The Starship Troopers series is about as basic of a plot as you can get. It's the same suped-up space marines blasting the bits off of an evil alien menace. There's power armor, giant guns, gory glory shots, and a race of savage and monstrous space creatures begging for a bullet.

The Bugs are basically that, giant carnivorous bugs that have an appetite for brains. They've got bladed armor, sharp teeth, and incredible strength that makes them a force to be reckoned with. One of them is scary enough, but a swarm is the stuff of nightmares, no wonder it takes such a massive army to take these guys down.

10 DALEKS

Think about this, how notorious do you have to be in the realm of Doctor Who to have a movie based around fighting you?. The Dalek's are the Doctor's most recognizable and arguably most dangerous foe. A race of armored aliens with one end goal, exterminate all inferior lifeforms. No compassion, no emotion, no mercy, the Dalek's are by no means friends of Earth.

Inspired by the Nazi party of WWII, the Dalek's consider almost all races other than themselves to be inferior. They're quick to destroy and nearly impossible to vanquish. Thankfully, we have the Doctor as the one all Dalek's fear to steer the TARDIS to victory. It takes more than a few laser blasts to keep the good doctor down, no matter the number of Daleks that try.

9 MARTIANS (MARS ATTACKS)

Inspired by the trading cards of the same name, Mars Attacks is Tim Burton's cheesy and hilarious reimagining of War of the Worlds. The aliens are over-the-top with shiny spacesuits, bulging eyes, and a skull-like face that makes them equal parts goofy and grotesque. But if you thought our first Martians were vicious, you've not met these guys.

Where the first Martians had tripods, death rays, and warships, these Martians have all those and much more. From giant robot mech-suits to flamethrowers that roast up congress, creeps are like something from an evil Looney Tunes episode. The movie is considered a cult classic and we highly recommend anyone who wants to see something completely out there, and we mean all the way out there.

8 KAIJU

Is it cheating to include aliens from inner space? Any giant creature from another world that requires a giant robot to fight it is definitely worthy of a spot on our list. These terrors from beneath the sea are some of Guillermo Del Toro's biggest and baddest beasts, some making Godzilla look like an angry puppy.

Pacific Rim's mega-sized monsters put a different spin on the alien invasion motif. Instead of coming from another planet, we are a pest that lives on theirs. There's a certain kind of horror at the back of our minds when we think about just how small humanity can be portrayed with giant monsters like the Kaiju, but it's nothing a few locked and loaded Jagers can't fix.

7 EGO

Though he lacks rayguns or technologically advanced weapons, Ego does have one of the most destructive arsenals on the list. Don't let the beard and the charm of Kurt Russell fool ya, he's not here to make friends or play catch with Star-Lord. Though he might be a silver-tongued spaceman, he's got more on his mind than interplanetary exploration.

His reveal in Guardians of the Galaxy: Vol 2 was surprising, sinister, and absolutely stunning. Ego's endgame was to spread his essence across the galaxy and consume the planets' essences to make himself a god. Looks like some people want to rule the galaxy, others want to make it in their own image.

6 KILLER KLOWNZ

In space, no one can hear you laugh... Well, these freaks are no laughing matter. Killer Klowns from Outer Space is practically the king of B-movie schlock, but it features some of the most horrifying creatures on our list. With some scary creature effects and memorable scares, this is a flick that's more freakish than it is funny.

Props to the filmmakers on taking nearly every alien movie trope and putting a creative creepy clown twist on it. Their spaceship is a circus tent, they shoot popcorn and cotton candy rayguns, and they collect people in pods like the Body Snatchers. Mix that with their fiendish faces, scary synthesized laughs, and appetite for humans and you've got one heck of a horror film.

5 SYMBIOTES

Ravenous, unstable, and unpredictable, these inky beings of the Marvel universe have been lurking about for decades seeking victims and hosts alike. Venom, Carnage, Toxin and all the rest make our list for their voracious appetites, sharp teeth, and nose for adrenaline. From Spider-Man and Eddie Brock to The Guardians of the Galaxy, these parasites have had a long and impressive reign.

The creep factor on these guys is particularly high for something out of the Marvel canon. Their tendrils, teeth and insatiable drive make for one dangerous species. They can climb walls, infiltrate just about anywhere, change into anyone or anything, and some (namely venom) have a biohazardous bite. Needless to say, Spidey's got his work cut out for him.

4 THE THING

We've talked a lot about enemies hiding in plain sight, but that was a multitude of a species. Imagine a singular creature that had the exact same power. That's exactly what John Carpenter did in his 1982 film, The Thing. A retelling of The Thing from Another World, the alien in question not only rapidly grows and evolves but can assume the form of any victim it has ingested.

The Thing is like a virus, its goal is to spread and consume the world, contaminating everyone and everything it encounters. Fortunately, MacReady and his crew of scientists are fast learners and soon do battle with the adaptable adversary. In a dazzling display of creature effects, we get a monster masterpiece.

3 CLOVER (CLOVERFIELD MONSTER)

This Godzilla wannabe is not your average Kaiju. When this creature from another dimension lays waste to the cityscape of New York, it brings more than teeth and claws to the party. The monster is not only a juggernaut in terms of size and ferocity, but it's not the only interdimensional terror the humans have to worry about.

The beast not only sports an enormous size, destructive nature, and booming roar, but it comes carrying monster sized lice that fall off of their host's skin and onto the streets. These things are nearly as monstrous as their giant host, feasting on humans and granting them grizzly fates with their bites. Creative, destructive, and monsters in its skin, Clover is one frightening force of mayhem.

2 XENOMORPH

Say it with us now, "In space, no one can hear you scream." With a nightmarish design by the late H.R. Giger, acidic saliva and blood, and a film series spanning six entries, the Xenomorph is normally the poster child for evil aliens everywhere. It freaked audiences out as early as 1979, and it continues being one of the pillars of the sci-fi/horror genre.

No matter which version of this maneater you come across, the best thing to do is run. Whether it's the face-huggers, the humanoid, the canine, the Neomorph, or that thing from the end of Prometheus, you're gonna have a hard time unless you have a flamethrower handy. We can't all be pros like Ellen Ripley.

1 PREDATOR

We're not gonna lie here, both Alien and Predator were neck and neck for our number one spot, but we gotta give it to the creature that took on Schwartzenager himself. The Predators get our number one spot not because of their number of victims, not because of their ferocious appearance, but because of their deadly efficiency. Any alien can hunt for prey for food, but for the Predators, it's all for fun and sport.

They don't call them Predators for nothing, these dudes are mighty hunters and are prepared for nearly everything. Sporting tons of weapons, gadgets, traps, and explosives, they're ready to send even the likes of the Xenomorphs to oblivion. They are a cool, calculating, and one-hundred-percent lethal threat to life on Earth.