Fungus gnats are horrible little flying creatures that love moist, humid terrarium conditions.
If you’ve ever spotted tiny little flies hanging out on the inside of the glass, it’s likely a gnat problem. And it’s likely to get worse before it gets better…
Unfortunately, pests like fungus gnats can enter terrariums in all sorts of ways, from substrates to plants and direct airborne invasions.
So avoiding them isn’t always possible, but thankfully, dealing with them is.
They can spread like wildfire, too, so it’s best to act early.
I’ve had fungus gnat issues before (it happens to the best of us) and was able to tackle them quite easily when I found the right solution. So, in this guide, I’ll give you five different ways to tackle gnat infestations and show you exactly how I did it.
Say goodbye to fungus gnats and hello to healthy terrariums – let’s go!
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5 Options to Beat Fungus Gnats In Terrariums
1. Predatory Mites
Okay, so I’ve had a horrendous outbreak of fungus gnats before.
They managed to infest half a dozen different terrariums all at once, and I’d actually given away a few of them to friends. So I needed solutions, and fast.
Honestly, this is far and away the most effective method I’ve found.
I know, I know. You probably don’t like the idea of adding more bugs to an infested terrarium, but this crack team of gnat-eating bugs has one job and one job only – they’re pest exterminators.
They’re extremely effective against fungus gnats and a variety of other pests like thrips and aphids. They eat the gnat larvae planted in the soil, so it’s tackling the problem at its source.
I’ve found that this solution takes a few days to get going, but there’s a significant difference after a week. After two weeks, I didn’t notice any more flies.
We ordered the same predatory mites for everyone who was looking after one of our infected terrariums, and they had similar results. Disaster averted!
👉 I used these kinds of mites from Amazon (don’t worry, they’re tiny).
I was worried they’d eat all my springtails, too, but that population is still booming. So that’s an unexpected win!
If you have a big tank terrarium (and likely a big infestation problem) and need a more powerful solution, you could also take a look at this Fungus Gnat Eradicator Mix.
It comes with the usual predatory mites, rove beetles, and various other beneficial microfauna and microflora. This combination tackles the fungus gnat from various angles and will help keep them away long-term.
Nematodes can apparently help too, but I’ve never tried them.
2. Vinegar Traps
As these gnats infested the house, we also tried adding vinegar traps around the room.
They worked to quell the numbers. We’d typically wake up to find a bunch of them floating in the cup each morning, so it could be worth adding to your terrarium if your infestation is bad (and you have the space to put one in).
Essentially, you add a small amount of vinegar into a cup and cover it will cellophane, poking holes in the top so that the gnats can get it but cannot escape.
Crude but effective.
That said, it will only catch the adults, and you need to make sure the holes are so small that any enterprising isopods can’t get in.
If you have a small terrarium that doesn’t have the space for a cup, try the next option.
3. Yellow Sticky Tape
An alternative to the vinegar trap is the classic sticky tape trap.
The gnats are attracted to the tape and proceed to get stuck. Super simple stuff, but again, you need to make sure it won’t catch all your beneficial bugs.
If you can DIY it, I’d recommend suspending the tape from the inside of your lid. That way, only the flying pests can reach it, and your cleanup crew is safely out of reach.
4. Carnivorous plants
Sure, this is more of a long-term play, but carnivorous plants can help keep gnats at bay.
There’s a wide variety of carnivorous plants out there, with varying degrees of suitability for terrariums (alas, venus flytraps are a terrible option for terrariums).
I’d start with Sundews or Pinguicula (also known as “Pings”). They’re small, relatively easy to care for, and suited to terrarium conditions. Pitcher plants can work great, too, if you have the space for them.
5. Dry it Out / Wait it Out
With fungus gnats being attracted to and highly dependent on moisture, it’s possible to fight them by simply reducing the amount of moisture in the terrarium.
Over time, this should really slow their spread.
I certainly think it’s a good place to start with any infestation; adding more water is only going to make the problem worse.
But I’d hesitate to recommend that you actively dry out a tropical terrarium. You’ll have no plants left to save if you do it too much…
Plus, cleanup crews require moisture and humidity to survive, so I really wouldn’t be taking this approach in a bioactive setup.
How to Prevent Fungus Gnats in Future Terrariums
Fungus gnats can come from a variety of sources, and sometimes it’s just bad luck.
However, some practices can help reduce your chances of them getting in.
- Quarantine your plants – I’m 99% sure my infestation came from a supermarket herb growing in the kitchen. So, I’d recommend you first quarantine any plants you buy (especially from supermarkets, garden centers, and big shops, e.g., Ikea) for a few weeks.
- Bare-root your plants – As pests can arrive as eggs in your soil/substrate, it can be a good idea to bare-root any of your store-bought plants and dispose of any attached substrate. The substrate plants arrive in can often be cheap and obscure anyway.
- Add a cleanup crew – Springtails, in particular, can help to prevent gnat outbreaks, as a healthy springtail colony can outcompete them for good. Unfortunately, my outbreaks occurred as I was building the terrariums, so the springtails were just getting established, but I’m confident they’d help a lot in the long term!
Did Any of These Fix Your Fungus Gnat Problem?
Armed with these solutions, I’m certain anyone can tackle a flying pest problem.
Have you gotten rid of your terrarium fungus gnats with these solutions? Or do you have an even better one that I’ve not mentioned?
Please let me know in the comments!