Ask Eartha: Fly-free worm composting |

Ask Eartha: Fly-free worm composting

Eartha Steward

Dear Eartha,

I have been doing all of the right things when it comes to using my indoor worm bin for composting. I maintain the right moisture level, keep fresh clean bedding and feed them food scraps regularly. The only problem is that my home is now being plagued by small flies. As soon as I open the worm bin, they fly out and now they are in my kitchen and on my house plants. What can I do?


Aside from the occasional parasite, owning a worm bin is a prime example of a symbiotic relationship. The red worms consume your family’s leftover food scraps and create nutrient-packed compost for the garden. In addition to the occasional meal, they need a dark and moist habitat. Overfeed your wiggly compost crew and you may attract some unwanted pests.

Fruit flies range in size from 1 to 2 millimeters, so it is easy for them to stow away in household plants. They can also sneak into our homes when we bring in fruit carrying eggs or larvae. Within a few days of sitting on the kitchen counter, there can be a large enough population to run a genetics biology lab.

There are several measures you can take to thwart an infestation. Avoid purchasing food that has over ripened, since the aroma is irresistible to flies. It also helps to eat your produce before it spoils; reach for a delicious pear next time you are craving the stockpile of Halloween candy.

Most homes with vermicomposting systems collect food waste in a container prior to feeding their worms. Placing a screen over the container will prevent flies from laying eggs inside. When feeding your worms, bury the food scraps two inches into the bin; this will throw flies off of the scent of the decomposing organic matter. You can also take some pre-worm feeding precautions like zapping your food waste in the microwave or boiling fruit peels in hot water to kill off fruit fly eggs.

When it comes to getting rid of a plague of flies, their strong sniffers can be their Achilles heel. You can build a humane trap for the flies and attract them using a banana peel. All you will need is a plastic container with four small (toothpick sized) holes in the cover. The bananas peel goes in the trap as bait, just be sure it isn’t in the worm bin or too close to anything that’s odor could distract the flies. Each day you liberate the hostages outside and in a week your home will be fly-free.

The less humane solution is to drown them in a mixture of apple cider vinegar and liquid dish detergent. Flies are obsessed with the scent of the vinegar. They fly into the cup containing the mixture, but the dish detergent is too thick for the flies to escape. You can also substitute vinegar for fermented beer or wine.

If your worm bin has become bug-ridden, then it may be time to clean house. When the worms are given too much organic matter, leftover food emits a pungent odor that attracts pests. According to the HC3 Master Mountain Composter Guide, one pound of red worms can break down around a half a pound of food waste per day. To ensure you have the correct amount of worms for your family’s food waste it is a good idea to collect and weigh your food scraps for a week. With the appropriate amount of worms and an adequately sized bin, you will need to harvest the vermicompost every six months. The raw and rich organic matter will do wonders for you flower gardens and blast your vegetable with a nutrient boost.

While this week’s article addresses the maintenance of a worm composting system, the High Country Conservation Center can provide information, guide books, and even red worms for those interested in taking the next step in a waste-free home. The changing of the seasons is an ideal time to get started, since the worm bin is a heck of a lot more convenient than digging through snow to find your outdoor compost collector.

Eartha Steward is written by Jennifer Santry and Caitlin Akkerhuis, consultants on all things eco and chic at the High Country Conservation Center, a nonprofit organization dedicated to waste reduction and resource conservation. Submit questions to Eartha at

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