Getting Rid of Fruit Flies and Fungus Gnats
There is no doubt that one of the MOST frustrating things about vermicomposting (and the thing I’m convinced is one of the real limiting factors preventing much more widespread interest in this field) is the other “critters” that can take over our vermicomposting systems. A couple of the worst offenders are undoubtedly fruit flies and fungus gnats.
I am definitely an advocate for “ecosystem rights” in a lot of ways (haha) – and really try to hammer home the point that a vermicomposting system is NOT just about the worms – BUT, I don’t have a whole lot of sympathy for the plight of these pesky flying varmints. Unlike with many of the other organisms that can pop up, such as mites, springtails, and white worms, it’s easy (for me) to think of fruit flies and gnats as “invaders” – we certainly DON’T need them involved in the process, and I certainly don’t need clouds of them up my nose!
Well, it just so happens that I have a fairly healthy population of both of these guys at the moment, so I’ve decided to have some fun (at their expense – MOOOHOOOHAHAHAHAHA!!). I placed an order for some parasitic nematodes (Steinernema feltiae), and set up a couple of fruit fly & gnat farms (pictured above) I hope to turn into nematode rearing cultures. As some of you will recall, I have tested S. feltiae before (see “Steinernema feltiae – Fungus Gnat Killer“) and I actually found them to be quite effective – at least initially. The issue is that the effectiveness seems to decline over time – undoubtedly due to the fact that the nematodes end up getting killed. For one thing, I discovered that scientific research has shown that the passage of these nematodes through an earthworm’s digestive system kills them (see “Steinernema feltiae and Red Worms“). I’m sure there’s also a fair bit of competition/antagonism due to the wide assortment of other organisms that can live in the rich composting environment.
Aside from wanting to work a bit harder at creating ongoing cultures of these nematodes (thus meaning I can apply them over and over again), I’m also VERY interested in once again testing to see if these nematodes will attack fruit fly larvae as well. I did set up an experiment to test this out last time around (see “Steinernema feltiae VS The Fruit Flies“), but I’m pretty sure conditions (outside during the summer) were too warm for proper testing.
Anyway…I will certainly keep everyone posted on my fun nematode experiments, but if I might shift gears a bit here, I think it’s not a bad idea to spend more time on this “Getting Rid of Fruit Flies and Fungus Gnats” topic in general (especially since a lot of you likely assumed that’s what this post was going to be mainly focused on).
Let me start by saying that both of these guys are a ROYAL pain once they become well-established, but of the two it’s the fungus gnats that are actually the most frustrating (in my experience). Unlike fruit flies, it can be very challenging to remove their “food source” since the larvae will feed happily on a very wide assortment of decomposing materials. You’ll likely need to be a lot more patient and thorough with your eradication efforts. On the plus side, really bad gnat infestations don’t seem to be nearly as common as is the case with fruit flies.
In both cases, PREVENTION should definitely be a very high priority! There are lots of different ways to lessen your chances of getting invaded. Here are some things to consider:
1) Observation – simply keeping your eyes open for any signs of small flying insects in your house is certainly an important part of the process! Fruit flies will likely first make their presence known in the kitchen – especially if you happen to keep fruit out in open bowls etc. Be especially wary of fruit from warmer regions – bananas, pineapples, melons are all regular fruit fly sources, especially if they have any sort of injury/lesion/disease. With fungus gnats you will want to be most careful with any potted plants and soil that you bring into the house since it’s not uncommon for them to already contain larvae and/or eggs. A good rule of thumb with your indoor potted plants is to let them dry out a fair bit between waterings. Constantly moist soil can become a prime gnat breeding ground. Generally, I’d also recommend keeping your worm bins a good distance away from any of your houseplants.
2) Careful Food preparation – This one applies more to fruit flies than fungus gnats. One thing I really recommend, if at all possible, is to freeze all your food scraps prior to adding them to your worm bins – especially in the case of uncooked fruit/veggie waste, and extra-especially (haha) with these materials that have also been sitting out for a period of time (in fruit bowls, scrap holders etc etc). Freezing these wastes will actually have a two-fold advantage. The obvious benefit will be the killing of any fruit fly eggs/larvae that happen to be in the material. Secondly, freezing can be a valuable way to start the break-down process (water expands when it freezes so this tends to rupture cell walls etc) thus making it easier for microbes to invade. You might want to let the materials thaw before adding them to your system though, since a lot of water can be released plus you don’t want to shock the system with a rapid temperature drop (could be helpful if your system is overheating though). Apart from freezing wastes, I also recommend chopping up (or even blending) materials before adding them since this will make them a lot more microbe- and worm-friendly, lessening the chances of other organisms gaining a strong foot-hold. On a related note, just generally feeding in moderation can go a long way towards avoiding any critter population explosions.
3) Physical barriers – I highly recommend always keeping a really nice thick layer of bedding materials up above your main composting zone. While this certainly won’t completely stop fruit flies and gnats from getting down below to lay their eggs, it CAN at least be a deterrent. It can also help to mask any odors that can attract these insects. Of course, having lots of bedding in your bin can also just generally be a great way to maintain a healthy environment, since it soaks up excess moisture, provides more worm habitat, increases air flow, and helps to balance the rich food wastes being added. You also may want to cover up your air holes with some sort of fine screening material, or even enclose the entire system in a big mesh (think mosquito netting) bag – perhaps a little extreme, but at least your chances of ending up with an invasion will be greatly reduced.
I think it’s safe to say that you should expect to be invaded by one or the other of these flying varmints at some point during your vermicomposting journey (or more realistically, BOTH of them – many times over! haha), so let’s now talk about different ways to deal with them once they become established!
When I’m not my usual mellow, laid back self (or otherwise engaged in various experimental pest breeding programs – haha), I like to employ a multi-pronged approach when attempting to get rid of gnats and fruit flies. Here are some of my suggestions:
1) Traps – various types of traps can serve as reasonably effective passive methods for capturing flying adults. They can also serve as valuable early warning indicators if you set them up before you get invaded. A very easy fruit fly trap can be made by putting a small amount of apple cider vinegar (or wine vinegar etc) in a jar with a tiny drop of dish detergent (reduces surface tension) and then covering the opening with plastic wrap before punching some small holes. Fruit flies will crawl through the holes and drown in the vinegar. Interestingly enough, I’ve discovered that these traps can also catch a fair number of fungus gnats as well – so I highly recommend setting some up either way.
Another type of trap that seems to work well for gnats is a sticky trap – especially one that’s positioned close to a light source. I’m not sure why, but gnats seem to be much more attracted to light than fruit flies, and even brightly colored sticky traps seem to draw them in. Some of you may recall my experiment with fly paper (hanging near a light bulb), and just how effective it ended up being for attracting gnats and bigger biting flies (see “Fly Paper – A Must-Have Vermicomposting Tool“).
2) Vacuum Cleaner – I’m sure this one will cause some snickering among those uninitiated in the ways of the the fly ninja assassin! (haha)
Joking aside, this is a phenomenal way to rapidly reduce the population of adult “breeders”, and thus greatly reduce the number of eggs being laid in your system. I highly recommend doing this at least once a day for best results. Aside from literally opening up your bin with vacuum nozzle in hand, also make an effort to round up as many of the roamers (those flying around your house) as possible. Again, a nearby light source will likely be a good place to start when hunting fungus gnats, and you may find a herd of fruit flies gathered around your fruit bowl or food scrap holder (speaking of which, you may want to throw scraps straight into the freezer once you have fruit flies in the house, since they will quickly make these containers a prime-time breeding ground if you don’t). It’s also pretty easy to make a powerful fruit fly attracting system (similar to the fruit fly farm shown above). Simply add a bunch of fruit scraps to a large plastic water/juice/pop bottle, along with some bedding materials (so it doesn’t get too sloppy and foul in there), then create a LOT of tiny holes using a pin or something similar. The idea is to allow odors out, while preventing fruit flies from getting in (although, it’s unlikely they’ll get back out even if they DO manage to squeeze in somehow). Fruit flies will congregate on or near this system and you should be able to vacuum up a lot more of them all at once as a result.
3) Remove Excess Food | Stop Feeding – As mentioned earlier, this is going to be a much more effective strategy for fruit flies than for fungus gnats, since gnat larvae don’t rely upon food wastes for their sustenance to the extent that fruit fly larvae do. Nevertheless, this is still a recommended approach for gnat invasions as well since every little bit helps. Feel free to continue adding bedding materials though – this can help to keep your worms alive without helping out the gnats and flies.
4) Let the system dry out a fair bit – This one will be especially helpful with fungus gnats, but should also help with fruit flies as well. The larvae of these pests thrive in wet waste materials and tend to be a fair amount more sensitive to drying than even the worms themselves. Not everyone will likely want to go this route, however, since it will more than likely require that you leave the lid off of your system for quite awhile (obviously resulting in more gnats and fruit flies being able to escape into your home) – but you might use it as a final step in the process, once the population of adults is clearly on the decline.
Ok – well, that basically covers some of my primary ways of dealing with these pests. Obviously various forms of biological control could be included in that list as well, but really the only promising option I’ve come across thus far is the use of parasitic nematodes – and again, I still need to test out this approach a lot more before I can provide a solid assessment (stay tuned)!
One last important thing to mention – most of what I’m suggesting here is intended for those with indoor systems. Unfortunately with outdoor systems there really isn’t a whole lot you can do to prevent either of them (well ok – you won’t likely end up with fruit flies if you aren’t using any sort of fruit/veggie waste), or get rid of them once they are established. I don’t personally find them nearly as frustrating in outdoor systems (not quite so “in your face” I guess), so perhaps this isn’t really a big deal anyway – but figured it was worth pointing out.
I am VERY interested to learn what approaches others have found to be successful for preventing and/or getting rid of fruit flies and fungus gnats – I’m sure there are plenty of effective methods not mentioned here. It would be really cool if we could turn this post into a sort of “ultimate” resource for dealing with these annoying pests.
Please share your ideas and methods below!