Sometimes, alien invasions do not start with spaceship attacks, but with subtle black stains on your lower calf. 

Stephen, the 28 year old red fox, hadn't even noticed the splotch the first few days. Not that any doctor on Earth could have helped him if he had, but perhaps they could have exercised a bit more caution in handling this.

He let off a sigh as he came home from work that fateful evening, weakly smiling at his girlfriend, his baby boy, six months of age, already sleeping in the crib in their apartment's master bedroom. He did wonder why he had felt so constantly tired for the past week, but this day was especialy bad. After dinner and TV, they both called it a night, his girlfriend kind of frustrated her man wasn't even in the mood for a blowjob.

As soon as you have kids, they just stop being interested in sex, she thought to herself.

Stephen drifted off to a dull sleep, feeling exhausted, while his girlfriend curled up next to him.
Later that night, his sleep became restless, nightmares haunting his mind - then, all of a sudden, he woke up in the pitch blackness of the bedroom, lying on his back and staring at the ceiling, unable to even move. His heart was racing, and something felt very wrong with him.

The blanket suddenly felt like lead, and he could feel his inexplicably erect cock already push at it from below. As he felt the cool air brush over his body, the pain set in, and he tried to scream, but all he managed to do was a deep throaty groan.

Not only was his cock painfully erect, his balls had also swollen to thrice their normal size and shed their fur, turned into black orbs. His belly was pumping and throbbing, making him look like he was several months pregnant, and also had become pitch black. 
Stephen strained to lift his head as he felt as if some strange force had tied him to the bed, watching his body change with growing horror. His cock throbbed and squirted out ropes of white seed, swelling further and further, one foot, then two, then stopping just short of three feet, his cum turning from white to pitch black. The cumhole became gaping and wide, teeth pushing out of its edge, a black tongue slithering around in its gaping tip.

Stephen finally managed to turn his pained groan into outright screams of terror as he shed more and more of his red fox fur, revealing shiny black skin. As the vixen next to him woke up from the commotion, he felt his belly contract and puked a foul bile over her face, his head feeling like it was going to explode any moment.

With his girlfriend choking and gagging, clawing at her face as the acidic puke sizzled on her skin, Stephen's changes became even more drastic. He could feel a sharp pain in his back as tentacles started to grow out between his shoulderblades, two pairs of extra black arms pushing out of his sides and an extra dick growing below the already massive black erection he was already spurting. His mind was unable to process all this - was he dying? What was happening? The last he heard were the wails from the baby in the crib, awoken from the commotion the little fox's parents were making. Then he went both deaf and blind, his heart thumping at 200 beats per minute before stopping abruptly.

*

The lifeform had been eliminated, and its organic matter replaced with drone material. The alien turned its faceless head and swiveled its newly-grown tentacles, sitting upright on the edge of the lifeform bedding. Its upper penis and lower penis were now at equal length, one equipped with a toothed mouth, the other serving as an ovipositor. It adjusted its stance, feeling its equally toothed rear hole being slightly moust as the lifeform had excreted some waste before its demise. It could feel there were two other lifeforms nearby, one presently dying with their cranial cavity exposed to corrosive drone spit, and one male lifeform of unsuitable age for conversion.

The drone decided to use the smaller male lifeform for fuel. It stood next to the bed, its black rubberized hooves clicking on the hardwood floor, and walked the few steps to the baby's crib. There lay the small organic fox, obviously in distress from the sound its parents had been making, tears running down the baby's face as the newly made rubber drone loomed by the bedside. One hand reached down and grabbed the small fox by the ankle, lifting him up and holding him upside down, one of the drone's pincers springing into action to cut through the baby fox's onesie and diaper, leaving the six month old's body exposed and stark naked.

It showed no emotion or caring as it sat down on the edge of the bed once more; ignoring the now dead female lifeform with the partially dissolved skull next to where it was sitting, as it took the small fox, spread the fox's legs and pushed its lower cock against the baby's anal hole. Crudely emulating sexual intercourse with a larger, adult lifeform, it pushed its member into the way too small hole, rupturing the baby fox's sphincter near instantly as the small one's wails turned into high-pitched squeals and screams.

Again and again, the drone pounded what had been the organic fox's offspring just moments ago, but the organic fox was no longer, his body consumed by an alien lifeform, now faceless and highly dangerous, with one mission - to acquire all suitable lifeforms to further growth of its race. The alien thrust deeply into the bleeding baby, and managed to push its cock all the way through, the baby fox's jaws snapping wide open as it slid down on the alien cock like a form-fitting condom, black slime dripping from the massive dick. It rubbed its member for a while, slowly grinding the now dead baby against its member, then pulled the dead body off its bloodstained lower dick and fed it to the hungrily waiting upper cock's mouth, teeth snapping around the corpse, chewing up the remains of the fox family's pride until the baby had disappeared fully.

The drone got up and scanned its surroundings; once it found out there were no further lifeforms found within this habitation unit, it walked to the bedroom window, ripping off the latch with one of its pincers and pushing it open, only to climb out and disappear into the darkness of the rainy night. It needed to complete its task.