just saw a fruit fly buzzing around my active carboy...

so im unfortunately in a somewhat crude apartment now in a foreign country. i brewed a pale ale for the first time here and made an improvised but i think effective airlock on a 4.5 gallon pickling jar. its a plastic bag with a small hole cut into the top for plastic tubing, the tubing is carefully taped onto the bag and the bag is fastened to the jar with an elastic band. tubing is going into a blow off tube bucket filled with water.

seems like nothing could get in, but i did see a single fruit fly within 2 feet of the carboy after not seeing a single fly in here for days. is there a real danger of infection? i know theyre insidious little bastards

I guess you will find out for us!!

As long as the outside of the jar, and tubing is clean and free of any yummy syrup, or wort spillage, there wont be much there driving them crazy to get at it. It sounds like it would be hard to get into for them the way you descibed it but they do have all day to try!

Yeah, your system seems sound. maybe spritz down the outside of the system with an oxygen based sanitizer and see if that helps. Seems like the safest to me, but honestly, I think you're okay unless you get a colony moving in right on top of your setup.

It only takes one fly for acetobacter to take hold.

Sounds like your solution is sealed... is your blowoff bubbling? If so, no worries at all, the fly is probably just attracted to the scent.

I've had those pesty buggers around my setup before. They're probably just attracted to the smell that comes out of the tubing/airlock, because they love rotting and fermenting things. If your system is sealed up you have nothing to worry about.

You should be fine... There are often some of these around my carboys and they never caused me any trouble.
Don't let them get in, however... if they do, they can even lay eggs (have seen it before in some must i kept reserved in a poorly closed flask) in there and it gets VERY disguting...