How to get rid of flies in a worm composting bin : a guide

“How do I get rid of the flies inside my composting bin ?” This is a frequent question found on the internet, in forums and group discussions on the subject of worm composting. There are as many answers as there are questions, however there is but one rule : prevention. Worm composting can be done without fruit flies and other pests. Indeed, many people who own a worm composting bin never had to deal with those annoying little flying insects. But it happens to some of us and when facing a fly infestation, one has to react quickly, especially when living in an appartment where they are most dreadful.

First of all, one should know that different kind of flies can take residence in a composting bin. Depending on their species, some are especially attracted by sweetness, others favour humidity and some even acidity. However, in this article, we deal with the overall issue of flies, without considering the specificity of each kind.

1 Prevent flies getting inside in the first place

Store your waste out of reach

• The most efficient option is to put everything diretly in your composting bin as quickly as you can : prevent them from getting in there in the first place!
• If this is not possible, store your waste in a closed box which you will empty as soon as possible. Do not let the organic matter decay inside the box! The ecosystem of the worm composting box is designed to receive fresh organic matter that will be first digested by mushrooms and bacteria. You wouldn’t want to eat old vegetables, would you ?
• Your last option is to store your organic waste within a refregirator, a solution much appreciated in summer if you need to cool down the compost

Bury fresh waste deep inside the composting bin

• Hide sweet organic waste deep inside the litter so that it does not attract flies. Out of sight, out of mind!
• Introduce enough cardboard inside the bin to regulate humidity and at the same time bring carbon to the organic litter : flies favour environments with high nitrate content and a high humidity level (if you have a doubt on the kind of cardboard that you can use, read this article)
• Grind egg shells to a fine powder that you will introduce with your waste to regulate acidity. Poultry egg shells are mostly made of calcium carbonate which will dissolve in an acid environment
• Always keep a “humidity cover” on your litter. It forms a solid barrier and limits access to the flies as much as as it prevents excessive evaporation

OK, prevention is good and all but if flies take refuge in the compost anyway, what can we do to get rid of them ?

2 Get rid of flies in your worm composting bin

To be honest, my first fights against flies haven’t been simple at all, especially in a 40 square meters appartement inside Paris. When you are comfortably sitting on your couch, enyoying a good book or movie, and a fly comes buzzing inside your ear, that’s to much to bear. The composting bin usually ends up on the balcony, if you are lucky enough to have one. That’s what happened in my case, however the exterior of my appartment is a bit on the sunny side and this exposure led to other issues after a few pretty hot day. But this is not the subject of this article.

So yes, from my own experience, I understand that flies inside an appartment can deter anyone from pursuing their composting experiments. Even outside these damn insects are a pain. So what can be done to stop the invasion ? What do we do to definitely get rid of them ?

Correct the litter composition

First of all, here are a few basics to better understand what we are going to do about our fly infestation. Mostly, flies are attracted by sweetness. To get installed and lay their eggs, they will favour a wet environement, acid and with a high nitrogen content. So the overall principle is to stop adding food, so that the compost loses these properties. But most of all, one has to be very patient!

Here is the detailed procedure

Add some cardboard in little pieces and stir them into the compost. The idea is to bring as much carbon as possible into the medium and to suck in humidity. The pieces will also help bring some air into the compost by giving it some structure. See here which cardboard you should use.

Stir well, in order to homogenize, bring in some air and bother the flies.

What have we achieved ? The humidity, acidity and nitrogen levels of the medium have been corrected. Now, it is important to evacuate the remaining flies inside the composting bin. Be prepared, you will need to be VERY patient.

Additional strategies

Make a barrier

Use a filtering barrier against flies :

“Keep out you damn flies! Nobody gets in!”

A barrier acting as a filter will allow flies to get out of the compost but will prevent them from getting back inside. That’s a smart idea but how is it actually done ? Spread a layer of soil at the surface of your compost, between 2 and 3 cm thick (you can also use coffee grounds but soil will be a little bit more practical). Soil allows air to get through and has a high carbon content. Flies will be able to come out of the compost through this barrier. However, new ones won’t be able to get inside the composting bin !

Get them out

Leave your composting bin open (without the cover) for a few hours and flies will start to come out in the open. You will need to be patient because you will have to repeat the process a few times a day at the beginning and stir the compost to get them all out. Take a good look at the sides and beneath the cover to check if they’re aren’t any new larvae.

This operation will take some time (between 3 and 4 weeks, depending on the number of flies in your compost). You absolutely need to repeat the process at least every day, without adding more food, until you don’t see anymore flies buzzing around your worm composting bin.

Be patient

As I have said at least a billion times in this article, you need to be very patient! Especially more so when you will have the impression during the first weeks that your actions avail to nothing. After you started taking action, the cycle of life of the flies (birth, life, breeding, death) keeps on going for a while. Hence it is perfectly normal to observe a couple weeks of delay during which they keep developing inside your compost before you can see any result in your careful actions.

Under any circumstance you must not give up and add food inside the composting bin to feed your worms because then you will have to start everything over gain. PATIENCE!

3 Further techniques for your worm bin

Build traps

In order to accelerate a little bit the evacuation procedure, you can intall in the composting bin a trap with banana peels inside (for instance a plastic bottle, keep it whole, so that the flies can get inside in the long term but can’t quickly come out of it). The sweet peels will attract them like nothing else! Empty the trap regularly, so that the banana doesn’t actually help them to develop further.

With patience and perseverance, it works! However the treatment will still take a few weeks.

4 What about the worms ?

In the meantime, our little darlings haven’t gone anywhere and still live in the compost, even though their life has slowed down a little due to the lack of food. When you are sure that there aren’t anymore flies, you can start incorporating food again. Do it slowly first, like you normally did in the beginning, becaus ethe ecosystem isn’t used to your steady stream of waste anymore. So take it easy for a couple weeks, just the time for all the living organisms to wake up from their lethargy. And most of all, avoid sweet things like fruit remains in the beginning, you wouldn’t want to go too fast and have to start everything all over again. When you started adding sweet food again, be sure to burry it deep inside the litter. Don’t forget to add a lot of brown cardboard to suck in the humidity, keep the litter well aerated and cover your composting bin with a barrier (for example a carpet of coconut fiber or a carboard piece).

There is no need for you to take the soil cover out of the composting bin once your fly infestation is over. In the meantime, the worms will have started stirring everythin up and will be incorporated in the compost when you will harvest it. Just be sure that it doesn’t form a dry crust between the litter and recent food. If necessary, stir everything up yourself.

5 What do I do with my organic waste in the meantime ?

Well, keep in mind that worm composting is but one of the solutions to deal  with organic waste. If you have taken the step to start worm composting (that’s a very good thing, congratulations!) it is only the technique taht you have selected among others. You may possess another worm composting bin or a bin in your garden, or maybe one of your neighbors has one or even your neighborhood (some have them in the local parks or in schools). You may have chickens also or there may be some in the vicinity. If you don’t have any of the options above then it is very sad, however you won’t have the choice but to dump everything in the garbage for a month. Keep in mind that it is just temporary. And most of all do not feel bad about it! It is for the sake of a healthy composting eco-system.

6 Conclusion

If you have read the whole article and understand French (sorry about that…), you can ckeck the video of Alain (The Easy Worm Composting Channel, La Chaîne du lombricompostage facile in French) who explains everything more visually!

What about you ? Do you have any additional tips and/or solutions to share ? Do not hesitate to contribute to the community by leaving a comment!