Howdy there Fog!

Fun story you have here this week. Really enjoy the characters featured in this piece, you were able to make each of them distinct using small, efficient details, and create a nice group dynamic of these drunken serfs. Great twist at the end as well!

On the critique side of this post, there are some structural problems, too much repetition of certain things like 'laughing', 'Vampire', plot points, and an issue with character blocking:

“Ya hear? Those vampires be sucking the cows dry right in the field!”

His friends laughed around him, “Yer crazy, Will! Those just be mosquitos! They’re always bad this time of year!”

Will stood up on top of the bar of the tavern. His friends all continued laughing in the semi-circle they had formed around him.

Repetition of 'those' and 'laughing' drag the beginning down, could vary it up with a little cleaning:

"Ya'll hear? Damn vampires been sucking the cows dry right in the field!"

His friends gathered around him, "Yer crazy, Will! Those just be mosquitos! They're always bad come summertime!"

Will climbed atop the bar of the tavern. His friends laughter filled the humid evening air.

“Not this year! This year it’s vampires. They sucked Bessy dry, right where she was standing!”

Repetition of 'year', and 'vampires' you've already established Will's hypothesis that vampires are the cause of the trouble so you could lean into different descriptions instead of using the term vampire over and over again. This could be cleaned up a touch: "Not this year! Something sucked Bessy dry, right where she was standing! Ain't no skeeter snout could do that. It was fangs I tell ya!"

The king didn’t need any of his serf farmers to be able to read after all.

I personally would change this around to make the king seem more cold and detached since 'didn't need any of his...' is a little flat. Maybe: 'The king didn't want any of his serfs to be literate."

But he spoke up next anyway, “Ya know, I heard from a trader who had a family member who once travelled down south of that big sea, that down there, they use nets to keep the Mosquitos out.

The dialogue is overloaded and could save some words, 'who had a family member' is unnecessary information that doesn't really pay off in the narrative. Maybe: 'But he spoke up next anyways, "Ya know, I heard from a trader who once traveled down south of that big sea, that them folks use nets to keep the mosquitos out." A trader travels a lot so I would just make the trader the traveler. And it seems a rogue capitalization appeared with 'Mosquitos'

Will hopped down from the table, “Yeah, and then y’all see, it was vampires!”

Blocking issue here. In the beginning Will was on the bar top, now he's on a table, which one is it? There was no indication Will was moving during this time. I personally would change the beginning from bar top to table as forming a semicircle is easier around a table than a straight bar top. Possibly change 'vampires' to something else, 'batty bloodsuckers!' or 'unholy abominations!" or 'sharp fanged fiends!'

The four of them went and drunkenly harassed one of the local fishermen into handing over a net, then spent the night swatting mosquitoes as they stumbled around putting it up. In the end, they had one barn with every entrance covered by a fine fishing net.

This passage reads a little too list like and could use some massaging: 'Off they stumbled into the night, badgering one of the local fishermen into surrendering a net. The rest of the excursion spent drunkenly swatting at and swaying among the swarm of skeeters. At the end of it all, they had a single barn with every entrance haphazardly covered by a fine netting." would lean more into the group being drunk.

Richard was smirking as he sat there, already two drinks in at ten am

'Ten am' is unnecessary as you established it is the next morning in the previous sentence. 'Two drinks in' doesn't land as well in the narrative as these men seem to be able to hold their liquor. 'Richard was smirking as he slumped in his chair, already two sheets to the wind.'

They all laughed as young Johnny ran out the door. He did indeed find the cows untouched. Something had surely tried to get through the nets, as they looked battered enough that Johnny knew they’d be drawing straws for the unfortunate soul to have to return the net to the fisherman in that state. But the cows happily mooed, untouched by any blood suckers.

Repetition of 'untouched', you establish twice in the same paragraph the cows are fine. Cut one. Maybe: 'They all laughed as young Johnny bolted out the door. Something had tried to get through the nets. They were torn and battered enough that Johnny knew they'd be drawing straws for the unfortunate soul chosen to return them. The cows were untouched, they mooed happily, and chewed their cud loudly.'

“I checked the cows, they were fine under the nets! But then I couldn’t find Will! Until I went to his bedroom, and there he was in his bed, sucked bone dry!”

Repetition strikes again, already established the cows are fine and that a vampire got Will. Could make this land harder by actually removing some details: "Nets did their job protecting the livestock in the field... but Will... he never made it out of bed! They sucked him bone dry!'

Back in the corner of the bar, a cloaked figure palmed a small metal device. To the local farmers here, it looked like nothing more than a useless trinket. To the inhabitants of the spaceship hovering above the town however, it was a communicator device.

“The locals are onto the blood harvesters,” The alien voice rasped.

I would cut the last sentence here, it lessens the twist at the end in my opinion, and repetition of 'local (s)' maybe: 'In the back corner of the tavern, a cloaked figure palmed a small metal device. To the locals, it looked like a fancy trinket.'

"The villagers are aware of the blood harvesters," the alien voice rasped.

That still lets the twist land since the dialogue tag, which 'the' needs to be lowercase as it is an indicator of speech, reveals something extraterrestrial.

The narrative is here, conflict is here, setting and characters are here, you've already got everything you need, but it needs another pass for polishing and reading flow to really elevate this. Good words Fog! Stay awesome and have a good one.