How do I get rid of these gnats? At my wits end trying to solve this!

December 25, 2019 7:25 AM

For probably 3 months now I’ve been noticing these little flies, slightly larger than fruit flies, in many rooms of our house. I made sure it wasn’t a trash or dirty dishes issue, and they’ve still been around with no drop off in numbers. It does seem like they tend to be in slightly greater numbers in our upstairs bathroom and our kitchen but they’re definitely in most rooms, generally.

Here are pictures: https://imgur.com/a/zZdsOyT

I believe I’ve determined that they’re fungus gnats.

I called our pest control guy and he came out, recommending we put plastic over house plants to see if they were coming from those. It doesn’t appear that they are.

He also treated the sinks and bath drains with something that would ideally kill off the gnats and larvae if they were coming from the pipes. That was two weeks ago and I haven’t noticed any difference.

I’ve just started covering our drains with tape to see if they’re coming from the pipes but again no sign of them this way.

I’m going crazy trying to figure out where these gnats are coming from and how to rid my house of them.

Any ideas, tips, opinions are welcome! Thanks!

posted by rbf1138 to Home & Garden (18 answers total)

Do you have windows? Window screens? Could they be coming in from outside?

I've had 'mysterious bug' problems which turned out to be gnat-like bugs which are small enough to get through our window screens. In particular, some of the screens had been replaced with cat-resistant window screen material which is stronger and has slightly larger holes.
posted by soylent00FF00 at 7:40 AM on December 25, 2019

Response by poster: Additional details I should’ve added: I’m in Atlanta, we have an unfinished basement (I haven’t investigated much down there but haven’t noticed the gnats while down there), we do have windows but most are painted shut and we haven’t had any opened to expose the screens to the indoors.

As far as figuring out if they are indeed coming in from outside, how can I setup to trap or identify an opening they’re coming in from?
posted by rbf1138 at 7:55 AM on December 25, 2019

seen em come from the drainage pipes before in an older apartment building fwiw
posted by some loser at 8:18 AM on December 25, 2019

The ID of Fungus Gnats looks pretty good and if it is indeed them, they have a life cycle of 5 days. So on one hand, a two week period means they are still coming from somewhere, on the other hand, any changes you make will need 5 days before you know it worked.

This article suggests they can get trapped just like fruit flies, and that technique is what I use. I put some red wine vinegar in a jar with a couple of drops of Dawn, place saran wrap on tope and poke a few holes in the top.
posted by jeremias at 8:52 AM on December 25, 2019 [6 favorites]

Do you have any bags of potting soil in the house (even seemingly unopened)? Either toss them or lock them up in a plastic storage container and see what happens after 5 days. Your pest guy is right that houseplants are usually the culprit, but it's the soil specifically that's the problem.
posted by Lyn Never at 9:01 AM on December 25, 2019 [5 favorites]

I had a similar issue last year. I then got into the habit of stopping my drains when they weren't in use. Problem solved.
posted by SPrintF at 9:08 AM on December 25, 2019 [1 favorite]

Nthing that it's the potting soil -- I had a similar problem earlier this year, and it turned out to be the potting soil in my houseplants. I re-potted everything and that took care of it.
posted by Janta at 9:18 AM on December 25, 2019

You can also use sand to stop them - once you find the plants they live in, cover the top layer of potting soil with sand. That prevents them from getting to the egg-laying soil zone, and they rapidly die off.

These fuckers have bothered me many times, always is a potted plant problem.
posted by chuntered inelegantly from a sedentary position at 9:30 AM on December 25, 2019 [3 favorites]

Also go crazy about standing water. Dry out the insides of your sinks, dry your dishes, etc. I've been there! This too shall pass!
posted by 8603 at 11:46 AM on December 25, 2019

We had these, and it turned out there was a slow pipe leak that created mold inside the walls. They were living on the mold.
posted by medusa at 12:04 PM on December 25, 2019 [3 favorites]

I have an indoor bug zapper and it's amazing. So gratifying! And it totally got rid of the gnat infestation last summer.
posted by kinsey at 12:07 PM on December 25, 2019

I have a small fungus gnat problem right now. The thing is that you have to get them at all stages. They are attracted to yellow, so I read something that suggested making traps by taking an index card, using a yellow highlighter to make it yellow, covering the card with petroleum jelly, and then placing this trap near where you’re seeing the adults. This won’t kill the larvae but should at least get a lot of adults.

My partner (who has worked in agriculture and dealt with them on a larger scale) recommended I buy this product called Mosquito Bits, which also works on fungus gnats. The directions say to put it on the top of the plant and then water the plant, but I’m trying to dissolve them in water right now to see if that will work instead. Anyway, the larvae eat the bacteria in it and die. I am doing this now so I can’t promise that it works. But the science is there. Maybe try this on your houseplants and potting soil?
posted by bluedaisy at 12:45 PM on December 25, 2019 [2 favorites]

We were going crazy with little gnats last year, and finally tracked it down to an old case of soda had a can of Coke that had degraded and leaked sweet syrupy gnat food for the gnats to feast on. I cleaned that up and killed as many gnats as I could. The lack of food quickly took care of the rest.

You said you noticed slightly more near the kitchen? For every shelf, clear it out, check every food product before putting it back. You'll hopefully find a food source causing the problem.
posted by nobeagle at 3:39 PM on December 25, 2019 [1 favorite]

In case they do seem to be in the plants and you can't get rid of them, be aware that the fungus gnat has a near-twin, the root aphid, that is far more tenacious. It's the worst.
posted by Edna Million at 5:53 PM on December 25, 2019 [1 favorite]

If you have house plants then treat with Neem Oil or a fungicide/insecticide you can pick up from like Home Depot or Lowe's. You can also treat the soil with a systemic. I've a ton of houseplants and had a bad fungus gnat problem, but once I started treating the plants themselves and the top layer of soil in each pot, I've not seen one in months. Additionally, you can pick up some sticky paper like this to catch them. Good luck!
posted by SoulOnIce at 7:07 PM on December 25, 2019

Beneficial nematodes in the potting soil is what killed the little bastards for me. (You can buy it on amazon but a garden store might be better because they must be kept cold.). Good luck!
posted by phoenixy at 7:35 PM on December 25, 2019

Yes! I had this from plants and it’s common to have potting soil contaminated with insect eggs. The only thing that worked for me was putting up yellow sticky cards that attract and then ‘catch’ the gnats. You reduce the overall population and the breeding population. It can take some time, but I now have zero gnats after having a large amount earlier this year.
posted by quince at 1:34 AM on December 26, 2019

Shot glasses with sugar water in them, but also a drop of dishwashing soap attracts and traps little gnats. This usually kills them off for me.
posted by agregoli at 9:20 AM on December 26, 2019