Vermicomposting 101: The #1 Cause of Worm Bin Problems

It seems to happen again and again and again.

Armed with a bin, some bedding, and a shiny new arsenal of composting worms, eager new vermicomposters, our fellow foot soldiers in the War on Waste try to win the war literally overnight.

And they often fail miserably.

Who can blame them? Our intrepid brothers-in-worms have not learned the crucial lesson a vermi-boot camp worth its salt would teach you; that overfeeding is the most common cause of problems in the worm bin.

The grossly over-optimistic rule of thumb that worms can eat 50-100% of their weight in organic waste each day is leading new vermicomposters to certain failure. So it’s high time we explore some common problems in worm bins and reverse engineer how overfeeding can cause each one of them.

Before we begin, it’s worth noting that overfeeding will not necessarily lead to ALL problems below.

But when the first step to solving the problems below is normally to STOP FEEDING, it should serve as a wakeup call that overfeeding is probably the start of most of our problems in the first place.

This article is part of a “Vermicomposting 101” series of posts aimed at helping the beginning vermicomposter. The read other “VC101” articles on how to start a worm bin, how to choose worm food, how to maintain moisture, and the differences between composting and vermicomposting, please visit the Vermicomposting 101 section of this site!

Common Worm Bin Problems


Your worm bin overheating typically indicates you’ve departed the realm of worm composting into simple rotting, which can resemble thermophilic or hot composting. While hot composting is a controlled aerobic process, the enzymatic and bacterial decomposition of excess food waste (especially when piled) releases heat, which can result in a further acceleration of bacterial growth which only makes the problem worse.

If this happens in a large open system like a windrow or a wedge, the worms can escape to cooler areas.

If this happens in a closed system like most home worm bins, then it’s probably lights out for your worms when temps zoom past 100°F.

If you’re able to salvage your bin after an overfeeding, there’s a simple way to prevent a rotting, overheating worm bin. Feed less.

Protein Poisoning (aka Sour Crop)

This is a really interesting  – and kind of complicated – way to kill your worms with overfeeding. As protein-rich foods break down, they release acidic compounds. And if these compounds exist in excess and are unbuffered by lime, eggshells or calcium-rich materials in the bin, they will pass through the worm’s crop (which is kind of like a holding tank where food is prepared for digestion downstream) in an acidic state where they will ferment in the gut, offgassing ammonia and alcohol, ultimately rupturing the worm from the inside out.

Sounds pleasant, huh?

This post from 2017 provides a little more detail how protein poisoning happens and what to do about it.

As food sources are more acidic and full of protein than bedding materials, the first step is to (surprise!) feed less.

Excess Moisture

Nearly all fruits and vegetables are at least 80% water weight. The more “fun” forms of worm food, like cantaloupe, watermelon, and pumpkin, which worms absolutely destroy, are 90-95% water weight, meaning that the late summer and fall buffets our worms enjoy in the US are a backdoor means of overwatering the bins.

Again, this isn’t a problem for a wedge or windrow where excess moisture can easily drain away to the floor or the earth below, and it’s less likely to be a problem in a breathable bin like the Urban Worm Bag, but if you’re vermicomposting in a plastic system like a single Rubbermaid bin, and you are overfeeding these water-laden foods to your worms, there’s a good chance you’re overwatering them too.

This can can lead to a compacted, anaerobic, and stinky bin.

Solution? Feed less. (You’re probably noticing a trend.)

Fruit Flies and Mites

With the caveat that a healthy worm bin can – and maybe should! – feature critters that aren’t worms, it’s a reality that indoor worm composters will not be pleased to find fruit flies, red mites or other unwelcome guests. To boot, our spouses and roommates may very well veto your vermi-aspirations if dinner gets interrupted by these pests.

I am gone from home quite a bit, meaning I moderately and consciously overfeed my indoor bins, somewhat inviting these problems. My silent partner in the Urban Worm Company, aka my wife, is not silent when fruit flies land on the rim of her wine glass.

I speak from experience.

In short, my indoor worm composting activities are at risk. Don’t let this be you! Again, feed less.

The Bottom Line

The endgame of mismanaging your bins isn’t the risk of overheating, fermentation inside the worms, a wet bin, or fruit flies; it’s the death of your worms or mass exodus and then death of your worms.

Not to minimize it, but this isn’t a huge deal if it happens here and there to just a few new vermicomposters.

But it’s a HUGE obstacle to the widespread adoption of vermicomposting in households if beginners fail by blindly feeding their worms a set ratio of food – which will often be way too optimistic – and then conclude that worm composting is not for them, or that it doesn’t work at all. And it seems to be the most common mistake new vermicomposters make.

So let’s throw out the wild estimates of worms eating 100% of their weight each day. A VERY well-known worm composter in California, who is probably running a highly-optimized system, estimates that his worms only eat 25-33% of their own weight each day.

In fact, let’s eliminate the use of ratios altogether and start from this rule of thumb:

When you underfeed, bad things happen very slowly. When you overfeed, bad things happen very quickly.

Keep in mind that your bedding is decomposing too, albeit much more slowly than food waste will. This means that if you go weeks or maybe even MONTHS without feeding a worm bin, as long as conditions like humidity and temperature are reasonable, you will return to find a worm bin that still has worms in it, doesn’t smell, isn’t too wet, and doesn’t have fruit flies.

Your worms (and maybe your wife?) will be happier for it!

Staying patient and deliberate with your feeding, and observing with your own two eyes when it’s time to feed again will keep you safe from the problems above!


53 thoughts on “Vermicomposting 101: The #1 Cause of Worm Bin Problems

  1. Yes. I have overfed a little, but my worms are happy and multiplying, however, so have the pill bugs, and at a much faster rate than the worms. I know they are more of a nuisance but I feel like the bin which is a homemade flow through is over run with them. when I gather castings from below, it may have just a few worms included but hundreds of baby pill bugs in only about a quart or so of castings. Should I be concerned? Like separate the worms and start over?

    1. So if it’s too dry how do you recommend getting the bin wet enough to deter a large portion of the pill bugs without making your bin too wet? And will the pill bugs just crawl out or how will their numbers decrease?

  2. I have ants that have made a home in my worm bin. I live in a tropical environment so cold isn’t an issue. I moved my worm bins under my orange tree for location convenience. Although they seem to be thriving, there are ants that made a home in the bins. Are the ants harmful to my bin? Thank you!

    1. Hi Lara,
      While I am not in a tropical area, the presence of ants actually indicates conditions that may be too dry. I think they would peacefully coexist, but you might end up spritzing the bin daily for a few days and see if that helps.

  3. Hi Steve,although I have been doing worm farming for over 14 years and one of your subscribers I always look forward to your newsy letters and will find something new to learn.I am a horticulturist by profession and find the two go hand in hand.

  4. Here’s a way to eliminate almost all your fruit flies; seriously. YOU HAVE TO COOK YOUR BANANA PEELS BEFORE PUTTING THEM IN THE BIN. 100% of bananas have fly larvae on the surface. By cooking banana peels first (I put mine in the toaster oven until their crunchy- easier to break up), I have never had a fruit fly problem in my bins. I’ve had 3; each one has over 10K worms in them. I have also added a copper foil collar at the top of my bin which worms don’t like. They are less likely to migrate out of the bin. It seems to keep everyone playing nicely in the sandbox.

    1. Now THAT is interesting Dawn! If you have just pinpointed a source of fruit flies on a VERY common worm food, then you’d just done everyone a huge service here!

      1. TY anything else I can do to prevent fruit flys? I’m new & starting my 1st worm bin. Right not setting up have not introduced worms yet. Been freezing my compost bags till ready. Do I need to defrost first?

      2. I watched a video on a gentleman who started a worm farm as a project for a college class and ended up turning it into a business, he dries out all the food ,fruit, everything he puts in has been dried, it kind of made sense to me

    2. I have an urban worm bag 2. It has been up and running for about a year. I lean on the side of underfeeding and I would say I run on the dry side of things. No water comes out when I squeeze but it will hold together until I jab with my thumb and it crumbles. My bag is indoors and the room it is in runs between 75 and 85 with high humidity… enclosed porch in Central Texas. It seems like my africans have been disappearing. I never see a worm ball. I bought a pound about 3 weeks ago to replenish my bag. The food I put in is mostly gone but the corn cob I put in isn’t decimated like I thought it would be. I use shredded paper as bedding and powdered eggshells as a supplement. If I water them I use a sprayer. Last time I opened the bag I had red mites but I can’t see anything else that is wrong. Are my worms dying? The bin doesn’t smell. I am not sure how to proceed. I haven’t harvested yet. Could that be a problem? 3\4 of the bag is loose and friable. Thanks for any help.

    3. I cook everything I feed my worms after first pureeing them in a food processor. My feeling are that the food will decompose faster making it more edible for my worms quicker.

      This seems to have worked well. My worms have multiplied 100 fold.

      1. I am wondering if there is much loss of nutrients if food is cooked or heated? I know they have that new kitchen gadget that works to cook and dehydrate kitchen scraps in a few minutes or hours, and I was wondering if it destroyed microbes and nutrients. If not then I suppose it is one way of dealing with some of the issues before feeding the worms with it.

  5. I love reading your posts because they are informational and written with humorous wit. Great job!

  6. Your information is spot on, It’s been very hard to get people to understand “less food is best”. Btw we used closed systems made of wood in various sizes this had made my Worm farming much more successful and less troublesome.

    1. Thanks Debbie! It sounds like you do your vermicomposting in a way similar to Heather Rinaldi of Texas Worm Ranch.

      1. hii!! I am using the windrow vermicompost bedding method and from few days I am noticing my earthworm are getting thin day by day and now they are thin as thread. what it means? and why this is happening?

        1. Hi Krati,
          I don’t have enough information to know for sure, but one thing to be aware of is that worms in a vermicomposting environment are not often as fat as they are in a worm breeding environment where they are fed food to fatten them up. If your worms are plentiful and not dying but just skinnier, there may not be anything wrong.

  7. I have a fruit fly infestation in my worm bag. There are whole life cycles in progress–adult flies, larvae, and white little maggots everywhere crawling up the sides and flap of the bag. I know that they are generally harmless, but still they make my skin crawl. On a positive note, my earthworms seem to still be happy. Any thoughts on how I can eliminate the fruit flies (larvae, maggots and all) without endangering my earthworms? Some people have suggested throwing everything out into the backyard but I am loathe to let my worms go.

    1. Try putting a soda bottle with banana and apple in the bottom just a small amount works for me . On top of the worm bed once or twice a day I put the lid on the bottle with a lot of flies in it I put it in the freezer for about 2 hrs and removed reopen put back in bed helps control flies

  8. I have found a solution to the fruit fly problem, and I hope you can help spread this info. The solution to fruit flies is called BTI. There is a good article about it here
    It is written by the former editor of Organic magazine, Mike McGrath. He is into vermicomposting and organic gardening and explains how BTI only kills fruit flies and does not hurt any other living creature especially worms.
    The stuff I buy is called Summit Responsible Solutions Mosquito Bits. I have been living fruit fly free for over a year after using BTI with healthy worm bins.

    Hope this helps

    1. Hi Mike – I just read your interesting suggestion of the Summit Responsible Solutions Mosquito Bits. Do you put a sprinke a small amount right in the bedding – as that’s where the fruit flies hatch.

    2. Just FYI: BTi doesn’t just kill fruit flies. It kills ALL flies, including mosquitos (this is BTi’s primary use), midges, shore flies, syrphid flies, tachinid flies, and on and on. We all know that mosquitos don’t breed in compost bins, so we can table that discussion for now. Like most pesticides, BTi has its place, but it is important to understand how it affects other creatures, especially if we’re later going to release this stuff into the environment. For instance, if you apply it to your worm bin, and then you use the castings to feed the plants in your garden, you will take care of the fruit flies and the shore flies, and likely a number of other pest species as well. But you’ll also run the risk of killing off the tachinid flies and syrphid flies that pupate in your garden soil, and that can have some pretty serious unintended consequences in terms of your garden being able to self-regulate pest populations.

      You might consider lightly cooking some of the riskier stuff (banana peels, as above?) to get rid of fruit flies. Something like a minute in the microwave? You could also likely freeze stuff to disinfest it, but it would take a looong time. Like weeks.

    3. That’s good info. Thank you. I haven’t even started worm composting yet. I am still researching it. I did once have one of those multi-storey worm composters. I brought it inside for the winter. I hadn’t had it long. I was not producing enough food for them. One day I looked in the bin and it was still clean. There was paper bedding where it should be but not a worm in sight. No worm castings and no food either. I don’t know what happened. The bin had not been disturbed.

  9. I have one of those worm high rises (vermihut?) . When I lift up a floor to feed a lower floor ther are always lots of worms danglingdown. Does anyone know how to lower the floor and not smush the poor worms? Thank you all, and especially, thank you Steve for running this site.

    1. Eesh, I am not sure. But I guess I am wondering why you would lift up a tray to feed the worms below. The intent of the stackable trays is to promote upwards migration, so you might have the migration of the worms backwards?

      1. Oh!!!! I’m so glad I asked! I put food in all 5 trays. I’ve got LOTS of worms now. Obviously I’m a bit of a newbie! Thank you so much for your response!

  10. Iam from Colorado,I have My worm bin outside .I had nearly 1000 to 1500 worms .This week I was out of town so my family forget to bring it back inside home ..half of my worms die due to cold ,so my question is should I have to separate the death worm and live worm from bin or not .does it cause a problem for live worm for composting.

    1. Hi Adu,
      Sorry it took me so long to respond! This stinks that this happened to you, but there is no need to remove any worm mortalities. Theier remaisn will become part of the vermicompost ecosystem very quickly!

  11. OK, this is timely for me, and I searched it b/c it seems my worm bin is heating up too much b/c I showed someone feeding, she said, “Oh, let’s put the rest here then!” and I did so. Now it looks like overfeeding – So What do I do to Salvage that situation? I don’t want to overwater by putting say, ice cubes in the bin, but how to reduce the temp (on the east side covered patio in south FL getting a bit of angled morning sun and none in the hotter part of the day, sitting back under about 8 ft from the edge of the roof. But south FL has been in the 80’s anyway just the temperature.

  12. I live in Texas and keep my bin in the garage. I noticed all my worms are on the sides of the bin and not in the middle what does that mean. It can get pretty hot here in the summer. I have the urban worm bag v2.

    1. Hi Oscar,
      I’m not sure if I have enough information to be able to tell you for sure. Would you be willing to send me a picture of the inside of the bin? My e-mail is [email protected].
      Cheers….and thanks for being a customer!

  13. I just submitted a comment and realized you might need a little more info. The red mites are a new thing and they are not in the bedding that I can see but up on the black edge at the top of the bag in palm sized groups. They are fast moving. I don’t see how my bin is too moist but mites would suggest that. I bury the scraps. And add shredded paper each time I feed which is usually every other week. I probably feed about a quart jar amount of food. Lately there have been quite a few tomatoes. Maybe my bin is now too acidic. How do these mites get in when my bag is indoors. Ugh. Are the mites killing my worms?

    1. Hi Shawn,
      So sorry for my late reply. I am not sure what is happening, but mites will not normally attack worms unless the worms are already dying. Let me ask some folks who use the UWB with Africans (I do not so I’m not the best source) and get back to you!
      PS – please feel free to e-mail me at [email protected]!

  14. Hi! Firstly, awesome tips here! I definitely learned a lot!

    I’m very new to vermicomposting – about 11 days into it – and since 2 days ago I’ve noticed some problems already…mass exodus of worms seem to be happening at the top of the bin. Based on your tips here, it does seem like I overfed and that the bin is heating up very much. Based on touch, it feels like the inside of certain parts of the bin are at 35 celsius or more.

    I live in the tropics and it is summer here now, with temperatures in the high 30’s constantly, with the heat index feeling like 40-50 at times.

    Other than dialing back on feeding and adding ice cubes every now and then, what else can I do to keep the ANCs from escaping?

    The bin is a black one that sort of looks like this:
    Then I drilled a row of 1/8″ holes all around the upper part of the bin. And since the start of the worm exodus 2 days ago, I added holes on the lid; 3 rows all across the mid part of the lid.

    What else do I need to do in order to stop the worms from escaping, and then dying?

    1. I think some people put a lightweight weed barrier across the top rather than putting holes in the lid. It lets air in. I am not sure what they do to hold it in place. Does anyone know please?

    2. I know it’s a bit late now but thought I’d say for future reference, I know people use 500ml bottles filled with water and frozen and change them every few hours when defrost, and if the bins getting wet with the condensation from the frozen water they put the bottles into ziplock bags so that it melts into the and not the bin.

      Also i personally don’t have lids on my bins as have found that the lids make condensation with encouraging the worms to follow the moisture, if you want to use lids as you stacking them I have seen someone put sheets of cardboard on top of the bedding and then dry the walls so you know it’s dry before closing the lid , that way the isn’t the moisture as you have dried the sides and lid and the cardboard or I use newspaper keeps the moisture under and so doesn’t go up the sides.

      Hope these ideas help but if you do have any problems with anything my best place for information immediately is YouTube. There is a lot of professional worm farmers on there including these guys and others that sell worms and castings etc. and there is probably more then one video that can help answer your question, just search how to stop worms escaping. For this reason.

      Hope this helps and hope you managed to sort it. Good luck with your future worm journey

  15. We’ve had our worm 360 for 6 months and we are still on the first bin!! We should be long into the second bin by now. We can’t figure out why they aren’t producing which makes living with the fruit flies very annoying. We don’t feed often and follow the tips throughout the internet.

    1. Hi Maggie,
      I can’t be certain, but most people run their bins too wet and most WF360 owners assume that their vermicompost should be producing leachate because of the tap at the bottom.

      If you’ve got a fruit fly infestation, then I would assume the bin is overfed and/or needs more bedding.

      I hope this helps!

  16. I have snails in my worm bin. I have no idea how they got there, but they are thriving. Is this a problem?

      1. Excellent article on this. I have clay soil in Phoenix and mistakenly thought I could throw some worms in there to help. I am learning.

        I see you are in Plymouth Meeting! I’m from Norristown. I fondly remember going to the mall, sitting at the fountain and shopping at Woolworths, and Buster Brown. That was a long time ago! Lol

        1. Oh man, there’s hardly a store open in that mall any longer. The stores on the outside are doing great, but inside, it’s really sad!

  17. I just found your bei good column here. O have been very successful with my inside worm bins in the past, but this current one has loooots/1000s of white tiny bugs. I obviously have not been very watchful, and they are everywhere there is food. Any thoughts?
    Thank you!

  18. I set up my bin (a well-ventilated Rubbermade tote) about three months ago with 1# of worms and shredded cardboard. I’ve been pocket-feeding the worms about once every 3 – 4 days. When I check back a couple days after each feeder the worms are swarming and chowing down on the food. and thriving. The substrate, shredded cardboard, is damp but not soaking. I have been following your advice to avoid overfeeding but wonder if the bin is at the point that I can feed more. Currently I’m thawing about 1/2 a pound of frozen scraps, chopping them in a processor, and then squeezing much of the liquid out. My questions – would it be safe to double the amount for each feeding? And is squeezing the moisture out a good idea? Thanks!

  19. I’ve had my original worm bin over 2 years, then divided to start a 2nd one. I’ve covered them with a sheer (old curtain) sewn with elastic around the edge all the way around so nothing gets in or out, but all the air circulation (was my thought). yesterday I noticed a coiled, slimy worm, when I investigated it was a flatworm (with a flat white belly). When I researched online, it said they are carnivorous, can eat snails, slugs, and earthworms! How could it have gotten in in the first place and do I have to go thru the whole bin to look for more? I live in Southwest Florida, the bin is in my screened in lanai, with blinds on the side where the worm bins are. Up to now I’ve never had any problems, so I’m mystified and horrified. Do you have any insights on this?

    1. Yeah, flatworms (aka planarians) are bad news. I have no idea how it got in there and yes, I’d probably root through the bin in order to extract any more that you happen to find.

Leave a Reply

Your email address will not be published. Required fields are marked *