So for the last couple of days a large number (50 - 100) fruit flys have been swarming around the kitchen and pantry, particularly noticeable at night. We have searched everywhere for their source, and have come up empty. I am looking for a good way to a) kill the ones we currently have (although I am sure they have a short life span) and b) any clever ways of perhaps tracking them back to their source, if one still exists.
More than you ever wanted to know about fruit flies.
The most important thing is to clean and DRY thoroughly. Fruit flies lay their eggs in even a tiny bit of sugary water. Clean your counters, under your appliances, behind your faucet, the bottom of the garbage can - all those little places that often get skipped over. Of course, remove any fruit, soda, beer, food scraps, etc. They might be in your drains - put some tape over your drain and come back in an hour. If they’re in there, they’ll be stuck to the tape. You can treat your drains with one of the products listed at that link.
When I have a really bad infestation, I throw out my sponge and use paper towels until they go away. They seem to like my sponge, even if I clean it and squeeze it out thoroughly.
I have always, naturally, associated fruit flys with fruit. Fruit I though was okay would be overripe and causing flies to buzz about. A particular nasty period in my life found me looking for a similar breeding ground so to speak. You might try looking under your refrigerator to see if there is somthing along the lines of a “drip tray” - I didn’t know it existed - be it does in some models and it can get smelly and disgusting and makes a nice home for this sort of pest. Good luck.
Have you poured boiling water down your kitchen drain yet?
Vinegar traps work for the live ones.
Please help me get rid of fruitflies.
Ways to get rid of fruit flies
Where are these wrassin’ frassin’ fruit flies coming from??
Fruit fly infestation – Help!
Where do all these friggin’ fruit flies come from??
After locating source, vacuum them up, they’re slow and easy, plus you have the satisfaction of hearing them scream all the way down the hose.
Are you certain they are fruit flies, and not drain flies? Drain flies are brown. In order to get rid of them, we were advised by an exterminator to use a foaming drain cleanser. Worked like a charm.
Actually, I had never before heard of drain flys. From I just knew they were about the size of fruit flies. With the knowledge that drain flys exist, I extended my search, and found their source in the bathroom sink in the basement. I am sure someone poured some sugared softdrink down the drain and they were living off that. Since it is a seldom used drain, I just ran the water to clean out the trap, then poured some boiling water down. There are still some live ones around, but they seem to be becoming fewer by the hour.
In the past, when I have had a fruit fly infestation, I have filled a wide mouthed jar with banana skins are apple cores and let it sit for a day. The fruit flies will collect there to lay eggs. Simply cover the mouth of the container with a plate and dump the whole mess outside somewhere. Repeat several times as necessary. Its not pretty but it works.
Oh, and don’t forget to clean up like everyone else has said.
Glued strips. You buy them wrapped in a small cylinder; whan you unwrap them, you get a very stickly strip about 2 feet long, which you fix on your ceiling. The glue smells sweet and attracts the little beasts, and they get stuck there. You might find it yucky to have glued strips with fly cadavers hanging down from your ceiling, but it works like a charm and will get to rid of them very reliably.
A friend of mine had one of those gelatinous eyeball toys. You know, they’re really soft and they might stick to a window if you threw one at a window. Turned out it was good for catching houseflies. Gross, but kind of funny.
I’m aggressive, and like to hunt down fruit flies with a spray bottle of soapy water. Socially acceptable murder! Woot!
You may need to get a foaming cleanser to rid the drain of all organic matter, any schmutz that’s in there will feed the little buggers. Advice from a friend who’s also a Terminix guy.
Barbarian! 
Hell, did I get my orthography wrong in that post!
Am I the first to say this? Whoohoo!!
Thank you, thank you, I’ll be here aaaaalllll week.