Fighting back the fruitless flies

November 2, 2023 7:38 PM

I have had problems with fruit flies a few times, but they've always been, well, near fruit. Currently, we are getting little tiny flies (possibly a little smaller than fruit flies) in every room. I would love to take care of this myself rather than paying hundreds to an exterminator, but I will pay an exterminator if needed. Any ideas? More detail inside.

They don't seem to be many, but I killed five in the office yesterday over about 10 hours. They're not concentrated in any one room and there is no visible source. We don't have food anywhere but the kitchen, and all of our plants are on the lower floor of our house. Could it be the litterboxes (which we maintain well?) The heat ducts? Are they feeding off microscopic traces of the hairballs my cat horks up weekly? (We clean really thoroughly, but I'm at my wits' end and grasping at straws here.)

posted by rednikki to Home & Garden (10 answers total)

These might be fungus gnats and not fruitflies? Either way I would make some vinegar traps, whichever method suits you. I'm partial to the mason jar with apple cider vinegar, a drop of Dawn dish soap, and holes punched in the lid. If you determine they are fungus gnats you may need to replace the top layer of soil in your houseplants.
posted by MagnificentVacuum at 7:57 PM on November 2, 2023 [8 favorites]

Fungus gnats is the first thing that came to mind too. Another way we deal with them is to put yellow adhesive sheets in/near potted plants. I don’t know the brand but ours are literally called “yellow sticky trap “ and googling for that will turn up a bunch of options.
posted by StrawberryPie at 8:03 PM on November 2, 2023 [4 favorites]

Former pest control person here. Do you have a clear run between the houseplants and the rooms where the flies are? If so, they may be fungus gnats (Sciaridae), which feed on fungi in damp soil. Control is mainly by making sure not to overwater plants, letti9ng the top two inches or so of soil dry out completely between waterings.

The other main candidate is scuttle flies (Phoridae), which mostly feed on damp and decayng organic matter of all kinds. control is mainly by removal of food sources. Check things like sink drains and the bottom of rubbish bins - I had an infesttion ot these in my kitchen last year which turned out to be a blocked sink drain which had leaked intot he cupboard below.

Neither of these types of fly are especially dangrous to humans or animals, although fungus gnats may carry plant diseasea, and phorids are generally unhygenic due to their food sources. Probably neither would have anything to do with your cats
posted by Fuchsoid at 8:06 PM on November 2, 2023 [12 favorites]

They could be drain gnats, although those are found loitering near ... drains. In fact, their appearance is my periodic reminder that its time to clean the bathroom sink ...
posted by intermod at 8:16 PM on November 2, 2023 [2 favorites]

Zevo flying insect traps stopped our problem dead. Got one for two rooms and now no flies. Kind of expensive but they work.
posted by tiny frying pan at 5:36 AM on November 3, 2023 [2 favorites]

Put yellow sticky traps in the plants, you'll know in 12 hours if they're coming from there. Put boiling water down all your drains except the toilets, which you can do monthly for maintenance. That's also a good time to check under your sinks with a strong flashlight for leaks.

The zevo traps, or just a cheap indoor bug zapper, are good at drawing them and zapping them, but that's more mitigation. Finding and eradicating the source is best.
posted by Lyn Never at 6:04 AM on November 3, 2023 [2 favorites]

I’m dealing with a similar situation now. In my case they were coming from houseplant soil. If you have houseplants search for “fungus gnats”. I am using yellow sticky traps stuck into the plant soil and watering with diluted hydrogen peroxide. It seems to be helping.
posted by bitbotbit at 10:14 AM on November 3, 2023 [3 favorites]

I successfully fought off a big fungus gnat infestation in my house. I started with the yellow sticky traps, and I echo others that you can buy some online or at your local hardware store and stick them in a plant or two, and you'll know soon enough if that's what you've got. So I knew I had fungus gnats, but the yellow sticky traps weren't enough to control them, so I did the hydrogen peroxide method: mix one part hydrogen peroxide with four parts water (I eyeballed it) and water all your plants with this. It doesn't hurt the plants, but kills the larvae. I think I did this for two rounds of plant watering (which is to say, I did included hydrogen peroxide in the watering can on the regular watering cycle with my plants twice). I have a bunch of plants (50+?) and used a fair amount of hydrogen peroxide, but I haven't had the fungus gnats come back in the three or so years so I treated them this way.

The yellow sticky traps get the adults, and the hydrogen peroxide gets the larvae, so you stop the cycle.
posted by bluedaisy at 10:51 AM on November 3, 2023 [4 favorites]

If they're fungus gnats—which generally means you have plants that need constantly moist soil—there is a bacterium that will wipe them out.

The advice to cut down on watering can be harmful to your plants. Plants that need constantly moist soil will not thrive if you underwater them, and soil fungi are not something you can or need to get rid of.

I use Bacillus thuringensis israelensis in my watering can regularly. It's a bacteria that infects mosquito and gnat larvae and it will solve your problem. In the US you can buy it as Summit Mosquito Dunks or Mosquito Bits. As a natural solution, it doesn't affect plants, pets, other organisms, or people. If you can't find those products, search for BTi.
posted by Wilbefort at 12:20 PM on November 3, 2023 [1 favorite]

If it is fungus gnats, I also recommend the biological control method - I think I got little wasps or something rather than mosquito bits? It was advertised as fungus gnat control insects. They were very very effective - one treatment got rid of all the gnats - and pretty cheap, so they might be worth a try even if you aren't completely confident in your gnat identification.
posted by In Your Shell Like at 6:39 PM on November 3, 2023