So out of curiosity when a stirge attaches itself to a player/victim the stirge basically auto hits with the blood drain ability not requiring a roll against their ac but since the stirge is on the victim and so close would the player be able to hit the stirge automatically or should you still have them roll

I haven't used stirges yet, but the way I see it is that the PC needs to roll against the stirge's ac.  My reasoning is that the stirge may be attached to a hard to reach location and be out of the PC's line of sight.  Because of the close proximity I could understand giving the PC advantage on the roll or, since the stirge is relatively stationary, reducing it's dexterity bonus to ac.  This is just one opinion and I can see others being just as valid.

You can just roll against the stirge's AC as normal. It's not easy to cleanly swipe a Tiny creature attached to your back by swinging a sword around. And even if the player takes some other tactic (like stopping, dropping, and rolling) it's easy to imagine that the tiny thing is fairly resilient.

Yeah once the Stirge attaches to a target it auto hits with its blood drain, and its blood drain damage after it attaches has no damage type so it's unresistable unless the DM counts blood loss as piercing damage.

As far as hitting it, where it attaches is important, and anything other than an unarmed attack would have to be made very carefully or risk hitting the person the stirge is attached to. This would be even more difficult if the person it's attached to is freaking out and moving around trying to get it off like most normal people would be. imo Players should have the option of taking disadvantage with no penalty for missing or taking a regular roll with a miss hitting their ally.

As written, no roll is required to remove the stirge. But removing it doesn't kill it, so it's a kind of CC. 

Against low level PCs, just give the stirge partial cover while attached. The chances of them killing each other with accidental hits is too high. 

House rule: for every round a stirge is attached, the victim must make a DC 10 with intelligence modifier, or the victim is too panicked to remove the stirge himself.

Nice house rule. If I were going to use this rule I might make it an intelligence save to account for any mental training, aka proficiency. 

 Back in my day (2nd & 3rd E), stirges were super sneaky. If you were last in the marching order, you could have one sucking on you and wouldn't even know it unless you made a perception-like check. The DM would just inform you that you were now missing x number of hit points and you have a large itchy lump on the back of your neck.

How does Stirge's skill work? After the stirge drains the 10HT and loosens, can it drain more HT? would have to wait a while? if they were created by magic, "conjuring animals" would change anything?

These are beasts? Guess this is going into the druid’s repertoire of wild shape forms.

Yes it auto hits, it already beat the characters ac and is attached

Since it's effectively tethered to the player I'd have the Stirge lose its Dex bonus to AC. That would take them from a 14 AC to an 11 AC. But any missed attack while attempting to attack an attached Stirge causes an automatic attack roll against the victim by the player attempting to attack the Stirge. If a player chooses to simply take their action to detach a Strige from its victim they can use a bonus action to deal 1 + their strength bonus in damage to the Stirge.

That's more wisdom or even con than intelligence.

I have come to say that I like stirge and have pet stirge

This thing is the definition of nasty. Almost died in a river with a Druid by my side underneath Baldur's Gate

"at the start of each of the stirge's turns, the target loses 5 (1d4 + 3) hit points due to blood loss." 

If the creature is still attached they lose hp. 

 Do Stirge have any natural predators or enemies?

small bat tpk'd my entire team

(Depends on DM) Mostly anything flying or has long reach like hawks or spiders.