My DM let me have a pet spider, I’m going to use it to kill people sneakily. Example: I pat someone on the back and the spider climbs on and bites them. I then pull the spider back by the thread (like a yo-yo) for retrieval, Everyone is none the wiser. Also, I’m naming my spider Muffet!🕷🕸

As they're spiders, I'd assume so, but my best guess would be that it would be a DM's call. If you are the the DM, then it's your call.

With the Find Familar spell,  the spider makes a great scout.  It can see in the dark, hide, crawl on ceilings, and detect other hidden spiders in the same web.

Our DM gave me one of these as a jumping spider.

She my pet jumpin spidey.

:D

The Find Familiar spell specifies that the familiar is not able to attack in combat, so a spider familiar shouldn't be able to deliver it's poison unless under special circumstances.

However, if your DM is choosing to allow it to attack, then on a successful Bite attack the target makes a Con save DC 9, and takes 1d4 points of additional damage on failure that is "typed" as poison damage. The spider's stat block does not specify any other effects from the poison.

Yeah... Owls only have a Strength of 3. So I'm doubly concerned that if this spider gets it's arms on an owl, it can easily conquer it in grapple and drag it it around where ever it wants to. The only difference between their grappling abilities is 1 point, because they are both tiny. 
There is not enough bug spray in the world to deal with spiders like these.

A spider familiar with the spell Dragon's Breath works wonders as a little stealth cannon.

thanks

"reach 5 ft" I mean okay, it's not a swarm but.... 
"I'm surrounded by spiders? Okay I'll walk away."
"Okay, they get opportunity attacks on you."
"But.... how do-?..." 

Yes

Either this or the owl are the best familiar. This one is so small you wouldn't see it, and with the intelligence of its caster it's nearly impossible not to come up with some game-breaking use for it. 

yez az a druid you can. but i think there iz a rule for climbing on people

FR though. I could strap a playing card with a Delayed Blast Fireball on it and have my spider plant it. 
The potential is limitless.

A commoner has around 4 health. Assuming they fail the saving throw, and the spider rolls high enough, a single spider bite could kill one, or at least have them making death saves

this is so fire and lit and skibidi!

spider and wild spider are the best wildshape forms imo, i love becoming those lil guys

Quote from oddpig1 >>

Can these spiders make webs? I was wondering because webs are a spell component and the spider could be used for detecting approaching enemies that touch it’s web if you have a spider familiar.

 Hoping so, just about to start a druid character and I would imagine being able to create webs would improve my wildshape's mobility. It looks like Giant spider has a web attack listed, but even there no rules for weaving a web or travelling by web launching and pulling yourself along. There's no mention at all of web creation for the smaller spiders (except perhaps the fiendish giant spider for which I don't have access to the rules), just the ability to travel across and detect creatures on an existing web.

scout spiders are amazing 

kill me

AHHHHHHHH