Sam finds the bite mark in the morning, rubbing himself dry after a shower. He angles towards the mirror and squints in the dim light, trying to inspect it more closely. It’s just a small red dot the size of a dime, a little above his hip, looking exactly like any other innocuous insect bite he’s ever gotten. Sam rolls his eyes - he knew, just knew he should’ve gotten the bedrolls out of the car once he saw the motel room. It doesn’t hurt or itch or anything, but still, it’s the principle. Damn bedbugs. He hopes Dean has a couple as well, in more sensitive places.
Scowling, he swipes some antiseptic over it and daubs on antibiotic ointment, just in case. Then he goes out to bitch to Dean about it. The mark fades and is gone by evening, and Sam forgets all about it.
A week later, Sam’s not feeling too hot. It starts as a tingle under the skin, uncomfortable and itchy, making him shift and writhe trying to find some relief. He’s not sleeping well, unsettled and prickly, and what rest he gets is haunted by vague disquieting dreams. The sides of his neck are slightly swollen and his appetite’s gone, so Dean thinks it’s the flu and forces some vitamin C and cold medicine on him.
It’s worse the next day. His throat is scratchy like he’s been gargling gravel, his joints ache fiercely, and he feels weak as a kitten, like his muscles are only half-connected, wasting away. Dean pays ahead two more days on the room and brings back soup and hot tea with lemon. Sam curls up on himself in bed, miserable and in pain, and winces when his hand brushes his belly. The skin is sensitive, hot and slightly distended and itching just beneath. Scratching doesn’t touch it, just leaves raw red stripes with no relief.
Sam tries to sleep, but every time he dozes off his dreams are filled with darting shadows, skritching and scurrying on razor-tipped legs.
He wakes up coughing, trying to dislodge the tickle in his throat. Dean gets him a glass of water, to no avail, and he has to force himself to breathe. Still, the tickle persists, climbing higher, and he keeps hacking and coughing, every jolt feeling like something’s crawling under his skin. Dean’s at his side, supporting him as trembling muscles threaten to collapse, patting his back to try and help.
Eyes watering, Sam stops, gulps in a deep breath, and heaves. He feels something leave his throat and come flying out into his cupped hand, slimy and hard.
Exhausted, he leans into his brother for a moment, breathing hard and shivering. He nods to the inquiry of “Better now?”, just glad the coughing fit is over.
Then he feels the thing wiggle in his hand. He looks down.
A small black spider sits on his hand, working itself out of the gob of phlegm tangling its legs.
Sam stares at it, numb horror stealing his breath, as the itch under his skin intensifies, gathering. A sharp stab in his belly makes him double up with a pained gasp, and he clenches his fists, the spider squishing between fingers. Dean shoves him back on the bed and rips his shirt up to see, only to flinch away with a loud curse.
Blinking back pained tears, Sam looks down to see a thin black leg poking through the skin, waving. Then another, and another, forcing the hole wider. A round glossy black body forces itself up and out, dripping tiny drops of blood over his skin as it moves out of the way for another three, four, six, ten more.
Sam gags on the renewed tickle in his throat as he watches the brood rip open their cocoon and come pouring out, leaving him hollow and empty.
The last thing he sees before he’s overrun by the wave of skittering darkness and dead eyes is Dean, horror-filled eyes wide, and a spider on his shoulder.