I was recently asked for some tips about dealing with flies around a worm bin. Unfortunately, I have dealt with the little pests from time to time. One big thing to remember with composts, is that flies, smells and molds, are all signs the balance is off in the bin. To much or too little moisture, air movement and food supply levels, are a few things that can throw off the ecosystem in your worm bin.
Flies, and more specifically fruit flies, can happen all of a sudden and can persist for weeks. I have heard banana peels, especially the ones where the tip is wrapped in plastic, are a bad culprit for fruit fly eggs. Whatever the source, here a few things that I do to help keep the bins from getting out of balance.
1. Freeze the food first.
I have multiple bins in various stages of compost, so I find it easy to keep a 5 gallon pail in the deep freeze and a small bin in the kitchen. We have a fancy porcelain compost receptacle for the kitchen counter. Although, I find the big yogurt containers from the grocery store actually work just as good, if not better.
I fill the pail in the freezer and then take it out a few days before feeding, to let it thaw out. Having said that, if I am going to feed the worms within a couple of days, I may not freeze the food first. Freezing the food beforehand helps to start the decomposition of the plant material. It breaks down the cell walls, and helps to hide the food smell from the fruit flies that may be flying around. This process also brings out a lot of the water in the food. Be prepared for the extra moisture, and food scraps that have been frozen and thawed have a funky smell. I know some people who freeze the food in plastic sealed bags. Its a quick open the bag – dump and bury.
2. Make sure the food is buried
When I open the particular bin and move the paper barrier (more on this in a minute), I will gently mix the compost around to break up any big clumps, and get the air to move around. Then, I move it all to one side and place the new food on the bottom of the bin. I make a little windrow and bury it with the existing compost. I also make sure if there is any left over food from previous feedings, that is buried as well.
3. Paper barrier
In recent years, I have adopted the technique of placing a 4 – 6 inch layer of shedded newspaper on the top of the compost. This seems to confuse the flies, and hides the smell. It works. In the horizontal migration bins, the paper is placed directly on the compost. When its time for feeding, I remove the dry paper and mix in the wet with the compost. Once the feeding is done, I put the dry paper back and add a little to maintain the desired depth.
In a vertical system, the top layer is paper, checking that the bottom of that level gets changed as it gets wet. This is the part where little kids can help out a lot. Who doesn’t like ripping paper?
In times of desperation, spray the top of the paper with a neem oil mixture.
That will kill the flies if the population gets out of hand. The oil doesn’t hurt the worms, and I don’t soak the paper, just wet the top of it. On one occasion, while trying to bring back a tower system for a client, I was using a apple cider vinegar trap outside the bin. It accidentally fell into the paper. Well I thought “there goes the whole clew”, but the paper absorbed the whole spill. The next morning there were no more flies, so I don’t recommend that method, however, desperate times…