Help! We’ve had pesky little fruit flies hanging around for over a month now. We’ve tried traps, cleaning the drains, everything in the threads linked, and they keep coming back to the point that we’re wondering about calling an exterminator. Has anyone tried extermination services? What could the pros do that we’re not doing?
Fruit fly infestation – Help! - Factual Questions - Straight Dope Message Board
Fruit fly trap - Miscellaneous and Personal Stuff I Must Share - Straight Dope Message Board
What are they eating?
Good question! We have apples out on the table but they don’t seem particularly interested. I think they’re in the back of the fridge, I find a few dead ones under the veggie drawer every couple of days.
I get them too. The “cider vinegar plus a bit of washing up liquid” trap certainly catches a fair few, and even more effective is the extension hose on my vacuum cleaner. It also helps to take out the rubbish more often.
They may come with the vegetables. I bought a cauliflower this Sunday and when I came home it crawled with fruit flies.
If your fridge has a drain pan then that’s a likely place for them to hang out. Clean it with ammonia and put a rag soaked in ammonia in it and place it back under the fridge every night for a week.
They also hang out in sink drains. Pour ammonia down the drain, enough to fill the traps, and put an ammonia soaked rag over the top of the drain. If you don’t cover the drain like that they’ll hang around the top of the pipe and some will survive. If it’s bathroom sink with an overflow drain that has to be plugged up also. After a week of doing this in every drain they should be gone.
If you have to resort to chemicals look at pyrethrin insecticides. Not toxic to humans and pets in the appropriate low doses. There are timed sprayers that release a small amount into the air at intervals that are very effective on flying insects. Fruit flies and other tiny flies that can hide out in the smallest of secluded spaces are tough to get rid of if you don’t find their hidey holes.
They don’t have long life spans so if they’re persisting, they’re laying eggs somewhere. The egg carapaces are pale brown and cling to the surface on which they were laid. They hatch into the usual insectile squirmy things which are white. Check garbage cans, bowls of fresh fruit, compost if you’ve got an intermediary indoor compost container, etc
You need to clean your fridge thoroughly and throw out what fruits and veggies you have. Take the bag out to your dumpster and deposit it. You have to clean everything because they lay eggs, and it is the hatched eggs that are repopulating the environment.
They’re hatching in the refrigerator? Yikes!
When I’ve had problems with them in the past, we would take a very fruity smelling body wash diluted in a large bowl with about 3-4 inches of water. This attracted them and they normally would find themselves stuck on the surface and would die. I’m talking hundreds on a 10" round bowl. I’m sure you could use a 9x13 casserole pan or dish as well.
The last time I had a bad infestation at my house, it was because of an old forgotten potato that apparently fell out of the bag and got lost in a dark corner of the pantry. When I finally found it, it was crawling with tiny maggots.
I always thing about how we must be eating their eggs and/or larva if they’re on our produce 
Think of it as a small bit of protein.
Also an excellent source of folic acid and other B vitamins.
When I’ve had fruit flies, just leaving a cup or glass of vinegar was enough of a trap to capture them. Cheap, easy and really safe.
Old wine works too; just add a couple of drops of washing liquid. Even if you never see any fruit flies going in, you hold the bottle up to the light and Wow! hundreds of the scientifically-useful blighters.
But I agree with those upthread that it’s essential to find the nest. If the OP has already checked all the obvious places then the fridge drainpan and sink are next. Oh, and of course behind or under all kitchen appliances.
We had a similar problem this year, it was over a month with them in the kitchen, we cleaned and cleaned and trapped and trapped, hundreds of them. Finally I convinced my wife to let me spray some bug spray (raid flying insect killer) which kills in the air and also leaves a residue on surfaces. We moved all the utensils, coffee pots, knife block, etc and I sprayed in that area. We left it overnight, cleaned it the next morning, and kept the traps out to get any stragglers. A couple weeks later they seem to be gone.
Ok we just found and killed at least 50 of them! I cleaned out the refrigerator, especially the drawers and underneath, several days ago. I washed all the fruit and veg in there with a white vinegar and water solution. There were maybe 20 fruit flies under the drawers but they looked quite dead or at least knocked out by the cold.
But the swarm I just found was in the basement. Our house is 95 years old with a mostly finished basement, but there’s a small storage room that we call the “cold room” and use as a pantry. The light in there had been out for months and my husband finally went in and fixed the wiring. So I was able to clean and found an old bag with 3 or 4 potatoes that had fallen into a cardboard box in a corner–it was swarming with fruit flies. I didn’t look closely enough to see whether there were maggots, but I wouldn’t be surprised. We had an old can of bug spray and sprayed the box, shoved it into a garbage bag and put it outside in the driveway. Let’s hope that there’s no other breeding source!
It’s too late to edit the post above so I’m posting again to acknowledge @bibliophage’s similar potato experience. And reminding myself to keep careful track of any potatoes in the house!
Oh, there were maggots…