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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!