Getting Rid of Fruit Flies With Diatomaceous Earth

My friend John is a serious Worm Inn fan. Back in the fall, he upgraded from the standard model to the Worm Inn Mega.

Bigger system, more worms, more processing power…but also more trouble if something “goes wrong”!

In John’s case, this came in the form of a fruit fly invasion.

Needless to say, he was at least thanking his lucky stars for that zippered lid!

Anyway – sometimes necessity can be a real mother!

Er…I mean the mother of invention! lol

After unsuccessfully testing out various fruit fly eradication strategies, John finally hit on something that (strangely) seems to be working really well.

Diatomaceous earth!

Here the run down in his own words:

Several weeks ago, I put probably a foot or more of shredded paper on the top. On top of this I added a apple cider trap that was sitting on a layer of cardboard. I was pretty excited about that because there were well over a hundred flies in it…probably 500 or so if not more. But it was in there for several weeks, and the flies were still coming.

So one night I remembered you talking about DE, and I have some. I took the fly trap out, and added probably 2 cups worth of the DE directly to the top of the shredded paper and cardboard. I left it alone. Within an hour or so I walked by and counted over 50 flies that were clearly dead or flopping around on their death bed. I was very amazed.

I also know that those are just the ones I could see. I saw a few that landed on the DE on the shredded paper and then fell in between cracks of all the paper. I left it zipped up the entire time. If I walked by the bin, I would hit the screen top to knock any flies into the DE. It has been nice knowing that all the flies eventually land on it and get coated, unlike the apple cider where not all of them would drink from it.

After about a week I noticed it looked damp and so I finally dumped them and just scattered the top again with a fresh coat of DE. I looked in today, and noticed there are only maybe 25 flies give or take. I am ready to open the bin up and start actively vacuuming again.

So I have been fighting thousands of fruit flies for more than a month before DE; and then within a week of adding it, I feel like I can finally win.

Really interesting stuff (and thanks very much to John for letting me share it here)!

While it’s hard to say if DE offers an “all in one” solution for getting rid of flying pests, it does at least appear to offer great potential when used as part of a multi-pronged eradication strategy!

I’m sure some will wonder if there is any chance of harming your worms with DE. Well, the good news is that this is very unlikely. As John touched on, the material becomes ineffective as it soaks up moisture, so the chances of it doing any harm down in the (moist) worm feeding zone are pretty slim.

I’m definitely looking forward to future updates from John (and anyone else who tests this out)!

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    • Darryle
    • January 30, 2015

    Is all DE the same? DE is commonly used in pool filters; is this the same stuff that is safe to use on worms?

    • Dave
    • January 31, 2015

    Darryle – I’m not an expert, but I do know the smart people recommend using ONLY food grade DE. Not the pool filter kind.

    • John W.
    • January 31, 2015

    I don’t know anything about pool DE. This was good grade DE. I got it from Tractor Supply. It’s pretty cheap and last forever.

    • John W.
    • January 31, 2015

    Food grade*

    • Debbie
    • January 31, 2015

    Can you clarify that it is safe to dump the DE back into the system and it won’t hurt the worms? I am facing a fruit fly issue just now that is slow to resolve. I have a 360 and I think I put too many rotten tangerines in it a week or so ago, because there were virtually no worms left in the top level, just rotten and slimy remnants of food and lOTS of fruit flies. I added damp shredded newspaper and an over ripe avocado or two, and it looks better, the worms have returned, except for the fruit fly cloud. Thanks, this is a great site, always learning something.

    • John W.
    • February 1, 2015

    I can’t promise there are no side effects from the DE getting into the worms. I did not notice anything, but I know my worm population is down, because i have not fed them in over a month, and the system was already newish; so there was not that much extra for them to process.

    • Anthony
    • February 1, 2015

    I’ve been using DE for a drain fly problem, and 1 month in haven’t noticed any real progress. What did work incredibly well were parasitic nematodes – those guys eradicated all traces of flies within a few weeks.

    • Texgal
    • February 3, 2015

    DE is a good (food grade) product but once it gets wet, it’s ineffective. I’d do as John did and put it on the top of dry material.

    • sam dockman
    • February 3, 2015

    oh my, DE has its place for pesticide but you all better had do your research if your concern is your worm bins. and that assumes you are using food grade, the product is basically silica – which is a naturally dehydrading substance – it’s effective on any bug/worm that walks thru it, as long as their undersides are soft and water absorbant. it is very commonly used as a wormer for the organic people of chickens, sheep, horses……….just saying, do your due diligence.

    • Michael
    • February 3, 2015

    I have Worm Factory 360 and I use DE on the top layer of newspaper to control fruit flies. It doesn’t get rid of them but it does reduce the numbers significantly.

    I was concerned about dehydrating the worms but I see no evidence of it so far (been using it about 2 months now).

    It is a little tricky to use because it is ineffective when wet, so the top layer of paper needs to be dry. Hmm, thinking online here but perhaps I can put a layer of plastic on the existing newspaper, then a layer of paper and then the DE. I try to find this thread again and let you know how it works out.

    • Triple "M"
    • February 3, 2015

    I have a few Megas and just can’t imagine how one could have a Fruit Flies infestation with this system…! With this being said I’m more interested in the cause as opposed to the cure …! Any information on the cause would be appreciated…!

    • John W.
    • February 3, 2015

    I can confirm that there has been zero effects to my worm bin. It’s okay if it is a dehydrating product, because my worm inn is plenty wet. I was a little concerned about it too, but after a while I just decided to try it. As soon as I washed it down with a sprayer the worms moved in and have been eating at the top for the last few days. I would NOT put DE directly on the top layer of compost while it was dry, I could see that being a problem, but I have had no problem with it the above process.

    Also, I work with some livestock and there is so much debate on if it works as an internal wormer. I know people put it in animal feed, but there is no proof that it works in the inside of animals. It does make a great wormer on the outside, if you dust the animals. But this observation would go along with what I have seen on the worm bin. If the dust is dry it kills bugs and worms, but if it gets wet, either by your stomach or by spraying it off in my worm inn, then it seems to be safe for bugs/worms

    Those are just my observations, not a fact that I can prove 🙂

    • Bentley
    • February 3, 2015

    Yeah, I have little doubt that it could potentially cause issues if it was dumped right on top of exposed worms, or if worms were dropped right into it. But the same might be true of the dust from a vacuum bag (yet, similarly, once it is moist it will be completely harmless). Also any sort of tiny parasitic “worms” it is reported to harm are completely different than earthworms, so I don’t think any parallels can be made there.

    But yes, I agree Sam that we should never just throw caution to the wind.

    • Verity Grace Turner
    • February 4, 2015

    I read to freeze my worm stuff if there were fruit flies – to kill the eggs they lay when I pop more food in the little bin.

    The bag had leaked when I went to take it out and was too lazy to put it in another bag and put it in the worm (factory) farm. Bad idea, resulting in little swarms whenever I opened the farm. I opened it often to let them out as they hatched so they wouldn’t keep laying more eggs, plus hung a sticky fly catcher above them and put bottles with little openings around with fruit in them and apple cider vinegar, plus a red-top fly trap, and damp big egg ‘boxes’ inside. And some little aromatherapy bottles with tiny openings, and fruit inside. There are fewer and fewer of them (at the moment, anyway). Moral of story – freeze first, plus it breaks the food down as well.

    • Edd
    • February 4, 2015

    Perhaps putting the DE into a tray and placing that on top of the worm bin would be a safer option?

    • marinemom
    • February 4, 2015

    Just an fyi on the pool grade DE, DO NOT INHALE THE DUST!! Food grade does not have that issue so I have been told but the pool people are adamant about being extremely careful with the pool DE.

    • Darryle
    • February 5, 2015

    A couple of you have already hit on this, but I learned a while ago (from Bentley) that freezing the food wastes prior to feeding helps eliminate potential fruit fly invasions as well as helping in the process of breaking down the food wastes. To answer Triple M’s question, the fruit flies can lay their eggs in food before your even think about feeding it to your worms. So I strongly support freezing all you food wastes first.

    • Verity Grace Turner
    • February 7, 2015

    My fruit fly problem is all but gone. The sticky flycatchers are just covered in fruit flies. There are fruitflies in the other traps but not nearly so many.

    If you microwave the flycatchers for a couple of seconds they unroll easily without breaking.

    • Amber
    • February 10, 2015

    just browsing thought the posts & came across this. Perfect post, as a newbie vermicomposter experiencing my 1st issue with fruit flies despite always burning scraps within the soil.

    I took a hairdryer to the visable flies & added a huge layer of shredded cardboard. Also plan to freeze scraps ALWAYS, from here on. Any other suggestions for catching flies? How often should I change traps, check, etc.

    • Jena Roberge
    • February 24, 2015

    Hello all, thought I would share this very informative website about diatomaceous earth. I work in the water treatment industry and am also an organic gardener as a hobby. I am familiar with diatomaceous earth both in my career and in gardening. It actually can kill most soft bodied small garden pests and has commonly been used to kills slugs. It works simply because the diatoms that make up the “diatomaceous earth” are microscopic sharp edged pieces of ancient algae that has basically become fossilized over time. The sharp edges literally slice and cut through the soft flesh of the pest which can cause it’s eventual dehydration and death. It is true that is absorbs moisture in general, but that is not the only way it harms the soft bodied creatures…I would not recommend using it much in a worm bin. Beneficial nematodes are much safer alternative and can be purchased on ebay for pretty cheap.

    • John W.
    • February 25, 2015

    I am not a scientist in any way, but I can tell you that I just sorted out the bin to get compost to sell, and there was nothing wrong with the worms.I made sure they could not get to the dust when it was dry.

    Also, I saw a couple people say “freeze your food”. I freeze everything. I don’t know how I got this infestation.

    • Texgal
    • February 27, 2015

    I know many people who use DE in their bins and it doesn’t harm the worms but I don’t understand “why” it doesn’t, sure seems like it would!

  1. I’m also dealing with a frustrating, unexpected fruit fly (or perhaps fungus gnat…it’s still tough for me to tell the difference) problem right now in my Worm Inn. The zippered top is helping keep the flies contained, but boy, are they multiplying!

    I’ve been using one of those handheld battery-operated tennis racket looking bug zappers and periodically opening up a small part of the zipper top, sticking it inside, and killing all the flies that are stupid enough to stay at the top of the Worm Inn. The problem is I think the flies are actually evolving to be smarter, hah. Most of them immediately start diving down to the lower layers as soon as the electric swatter starts zapping.

    I’ve also been cutting back on feeding and watering the worms…trying to kill off the flies before adding more fodder for them to keep multiplying in. I’ve already long since been freezing the food before adding it and until now that was successful.

    I moved to a new apartment about 9 months ago and shortly after, I started having these problems with flies. I think they were acquired during the move. A couple of months after we moved, I tried restarting the Worm Inn with all new bedding and food, and even rinsed the worms to make sure no tiny eggs from the flies were stuck on them. Within a week or so, the flies were back again. Maybe some had flown in the bottom of the Inn.

    Anyway, I was thinking about trying to restart they system again, but maybe I’ll try this DE method first. One question I have about it, though, is that once it gets mixed in with the overall system, if it dried out too much because we went on vacation and couldn’t water the system regularly, would it then become dangerous for the worms? Now, like Bentley mentioned in another post, although the Worm Inn does dry out easily, it can go for a month or longer without watering if necessary because there will still be a small, wet layer on the very inside that worms can get along in until the next watering. It’s not ideal for their productivity, but it won’t totally wipe out the system. I’m wondering if adding DE to the mix would cause problems in those times when we couldn’t water regularly.

    • Anthony
    • March 26, 2015

    Hi Angel,

    As I mentioned in an early comment, I highly recommend using nematodes rather than DE. They are harmless to the worms (actually, worms end up eating them) and in my experience far more effective for fly problems.

    • Texgal
    • March 27, 2015

    As Anthony said, beneficial nematodes should work.. as they will destroy the eggs. Maybe a 2 step approach is the answer, DE on the top of paper to kill the existing flies and b. nematodes to stop the next generation.

  2. Thanks for your recommendations! I live in China now, so everything I use has to be locally bought (I’m pretty sure customs would frown upon nematodes being brought over in my carry-on from the States!) I was able to find DE on Taobao (the Chinese version of Amazon/E-bay) but unfortunately, the only type of nematodes I can find are not the kind that affect gnat populations.

    I also tried some peppermint oil and clove oil after reading a comment about that on one of Bentley’s other posts. First, I left a cotton ball on the top of the Worm Inn for a few days…no noticeable affect on the gnats. Yesterday, I tried pouring some of the oils into a little cup and resting that on the top of my cardboard layer inside the Worm Inn. Maybe about 10 gnats were dead in the cup this morning, but that is a tiny drop compared to the total number of gnats still happily flying around the top part of the Inn.

    At this point, I think restarting the Inn and washing it out is going to be my best bet to quickly get rid of of the gnats. I’d like to get some compost ready for my plants, but I definitely don’t want to put on compost that’s full of fungus gnat eggs & larvae.

    • Anthony
    • March 27, 2015

    Hey Angel (that never gets boring btw:),

    In the spirit of Bently, i.e. experiments, why not split the two populations? Have one clean one, and the other all gnaty?

    But on the subject of clean, does anyone have any experience recycling/restarting an infested system? I use three white plates and chopsticks, so i’m sure someone has a more efficient method!

  3. Hi Anthony, I wish I had time to experiment more with my worms!

    I ended up cleaning out and restarting my entire system this past week. I’m glad I did…there were probably millions of gnats completely worked through the system. I now know what gnat larvae look like. Pretty gross! It’s strange because I think the baby red worms are cute, but I guess the white larvae look too much like maggots to be cute.

    The weather was very nice last Saturday, so I took the whole Worm Inn outside in front of our apartment building, put on a pair of rubber gloves, and started sorting worms from everything else. I was able to save over 100 of them, along with a couple of cocoons. I didn’t have the stomach to carefully sort through and get all of them out because the abundance of gnats and larvae was grossing me out too much.

    One note I should add here is that the Worm Inn really is amazing at giving worms enough oxygen but also keeping a moist, healthy layer for them to thrive in. To try to starve out the gnats, I hadn’t fed or watered the worms for probably more than a month by the time I cleaned out the system, and in the winter time our storage room can get quite cold, but the worms were still doing great in there! They didn’t seem bothered at all by the gnats, the lack of food and water, or the cold. I found plenty of baby worms and cocoons. They are very resilient creatures!

    I put the worms I saved into a plastic tupperware container, along with a small amount of compost, bedding, etc. from the old system to keep them alive but not so much that it would attract the gnats again. I read online that adult gnats can survive for about a week, so I decided to keep the worms in the little box with a large air hole poked into the top for 6 days to give time for any wandering gnats in our apartment to die out before I set up the Worm Inn again. The worms really hated being in the box, and I lost about 15 of them over the course of the 6 days. They decided to venture out and try their prospects in the corners of our storage room, but unfortunately, that didn’t work out so well for them. Luckily, most of them were smart and stayed in the moist box.

    I dumped out the leftover infested parts of the system under the bushes in front of our apartment building (probably not something I’d recommend in the US or Canada, but in China, nobody seems to mind that kind of thing). Then I washed the Worm Inn itself, first in the bathtub to rinse out as much of the dried up compost as I could and then 2 times through the washing machine. There were gnats worked into every nook and cranny of the Worm Inn, so I really wanted to make sure they were all dead before restarting. I hung up the Worm Inn to dry, and after a day or two when it was dry, I put it in the freezer. (Overkill maybe, but I really don’t want another infestation after all this!) I left the empty Worm Inn in the freezer for about 3 days.

    On the 6th day, after we hadn’t seen any gnats flying around the apartment, I finally got the system going again. I started with shredded cardboard and some frozen “smoothies” of the scraps from my freezer. I covered the scraps with more cardboard.

    Then before adding the worms to the system, I hand rinsed each one of them in the bathroom sink to make sure any microscopic gnat eggs would be washed off before restarting the system. When I started to wash off the worms, I noticed that a few gnat larvae had crawled to the top of the tupperware box and died, so I think it was definitely a good idea that I rinsed off the worms and didn’t just add them into the Worm Inn with any of the old compost materials.

    The new, clean Worm Inn has been going for a couple of days now and so far I haven’t spotted any gnats or roaming worms, so things seem to be going well.

  4. I disagree with the statement that DE looses effectiveness when wet, or that it’s only purpose is to dry out the insects and/or mess with their exoskeleton.
    teds t
    It can be washed off, but it continues to fight all kinds of insect activity when wet. My understanding of fruit flies is that part of their life cycle is as something that doesn’t fly, and if their life cycle is disturbed, then no more flies. Spraying it mixed with water is much more effective in most situations. It’s difficult to accomplish since it o mess with the mechanics of spraying, but once you figure out how to apply it, it’s incredibly effective. Anyway, hopefully that helps.

    Reading about people’s frustration at eliminating flies (which I hate with a passion) is actually affecting me (I have ptsd). I use a hose attachment and haven’t had any problems since. Only a small quantity is required and is safe for the worms. I imagine it’s actually beneficial for their digestion since its like little microscopic scrubbers passing through their systems.

    • Lorna
    • July 12, 2015

    I am so anxious to try DE and maybe nematodes. I am sick to death of sewer flies. I vacuum them every few days but I know I am not getting rid of the eggs.
    I do not want the sewer flies in my house. Yikes.

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