How to Prevent and Eliminate Fruit Flies in the Worm Bin

by Steve | Nov 7, 2019 | Vermicomposting 101 Series | 20 comments

The risk of fruit flies in the worm bin is pretty much a fact of life for anyone who wants to get started with vermicomposting.

The bigger risk – to me anyways – is that someone will encounter fruit flies and give up vermicomposting forever.

In an effort to prevent this, I created this article to acquaint you with:

the basics of fruit flies
what fruit flies are attracted to
how to prevent fruit flies
how to trap, kill, or eliminate fruit flies from your worm bin

Fruit Fly Basics

The fruit fly, or drosophila melanogaster, is a very common household nuisance. Though they has shortish lifespan of 40-50 days, these little jerks are prolific reproducers as a female will lay 40-50 eggs at a time, around 100 per day, and close to an estimated 2000 in her lifetime.

Take that Octo-Mom!

Don't Fear the Fruit Fly

Although fruit flies are a nuisance, they do not carry and/or transmit human disease like mosquitos.

These eggs hatch after only 12 hours and the resultant larvae grow for about 4 days before pupating for another 4 days before they emerge as adult fruit flies. And a female becomes sexually mature only 8-12 hours after emergence.

The optimum temperature for fruit fly propogation is 82°F/28°C, unfortunately very close to the 72°F-82°F temperatures where you want to keep your worm bins.

What Attracts Fruit Flies

Rotting, fermenting foods are serious attractants for fruit flies.

Fruit flies are attracted to moist environments with fermenting food waste. They like garbage disposals, kitchen waste baskets, and of potentially, worm bins.

Of the various wastes you might find in a worm bin, fruit flies are especially attracted to the very same sugar-rich foods that your worms will find the most attractive: pumpkins, honeydew, canteloupe, banana, watermelon, etc.

Fermentation is the anaerobic processing of sugar into alcohol or acid, so sweet, carbohydrate-rich foods like the ones mentioned above are prime candidates for attracting fruit flies.

How to Prevent Fruit Flies in the Worm Bin

I want to be upfront.

If you keep your bin indoors, do not promise your spouse, roommate, or significant other that your bin will NEVER result in fruit flies.

While vermicomposting itself is not difficult, vermicomposting with a zero tolerance policy towards any fruit flies ever will surely lead to disappointment.

But that doesn't mean that there's nothing you can do to prevent fruit flies or at least greatly prevent their proliferation in your worm composting bin.

Can the Urban Worm Bag Keep Fruit Flies from Getting In?

In a word, no.

While the Urban Worm Bag can make it more difficult for fruit flies to enter, they can still sneak in between the two top zippers and make their way in as tiny eggs and larvae on the food waste you introduce to the “UWB.”

Freeze Food Waste to Kill Fruit Fly Eggs and Larvae

The 1979 movie When a Stranger Calls features a scene where police tell Jill that the stalker's phone calls “are coming from inside the house.”

Likewise, if you're trying to prevent fruit flies, its helpful to know that they may very well be coming from inside your bin.

Because you put them there!

If you're in the habit of leaving food waste to just hang out before feeding it to your worms, it is highly likely that fruit flies are laying their too-small-to-see-with-the-naked-eye eggs on it. Fruit fly eggs measure about one half of a millimeter.

This means you are introducing the soon-to-be fruit flies to your bin.

So it may be a good – although not carbon-neutral – idea to freeze your food waste before introducing it to the bins to greatly reduce the initial population of fruit flies that you'll have to contend with.

Freezing food waste also has the added benefit of speeding up the vermicomposting process once it's thawed due to the rupturing of cell walls as the water inside them expands.

Keep High Levels of Bedding

One of the most common mistakes new vermicomposters make is forgetting about the importance of bedding after their worm bin is established. My hunch is that too many worm bin owners only consider bedding in the beginning and consider it an afterthought afterwards.

A low level of bedding relative to food waste contributes to wet and anaerobic conditions. As fermentation itself almost always occurs in anaerobic conditions, simply keeping an aerobic environment with high levels of bedding will help keep fruit flies at bay.

Note: An aerobic worm bin does not mean fermentation is not taking place anywhere. A healthy aerobic with a whole orange left to rot will ferment and attract fruit flies. Ask me how I know this!

High levels of bedding will also give you the option of burying your food waste underneath it.

Excellent Bedding Choices

Use one or more of the following to continually add carbon-rich bedding to control your fruit fly population.

shredded paper
shredded cardboard
aged horse manure
Urban Worm Coco Coir

Want to Learn More?

Check out 9 Awesome Choices for Worm Bedding

Bury Food Waste to Reduce Fruit Flies

Burying food waste in the worm bin under dry bedding or mature vermicompost makes for a less ripe environment for fruit flies.

Fruit flies deposit their eggs by piercing the skin of fruit, vegetables, and other targets of opportunity. Burying ripening organic waste in your vermicompost or under a layer of bedding will go a long way towards denying fruit flies a maternity ward for their little ones.

Skip a Feeding

Several Urban Worm Company readers suggested this one and it makes plenty of sense!

If fermenting food waste is attracting fruit flies to your worm bin, then maybe a little less food waste will help!

While the entire point of vermicomposting for many worm bin owners is to process food waste, you have to balance it against your tolerance for fruit flies. So if you've give your bin a good “workout” with a heavy feeding or two, give it a rest for a week.

Consider using an Urban Worm Blanket

Given the choice, fruit flies will lay their eggs directly on food waste. Failing the availability to access food waste directly, they'll lay their eggs as close to it as possible.

One option to consider to make your vermicompost bin a harder target is to use an Urban Worm Blanket.

Made from the natural fiber jute, an Urban Worm Blanket is unlikely to be a welcoming habitat for fruit flies seeking to propogate.

Intended more to help maintain a dark, moist environment in any worm bin, the Urban Worm Blanket may also be an effective countereasure against those pesky fruit flies.

How to Kill or Eliminate Fruit Flies in Your Worm Bin

Can't keep the fruit flies out of your worm farm? Do the next best thing and get 'em outta there!

Note: All of the fruit fly trap solutions below will be non-toxic to worms if they come into contact with your vermicompost.

Make a Homemade Fruit Fly Trap Next to Your Bin

A simple jar of vinegar with a small paper funnel inserted into it will create a very effective DIY fruit fly trap.

The little buggers can get in, but they can't get out.

24 hours should be long enough to thin the herd! Note: This could be risky to actually place inside a worm bin as it can be a bit top-heavy.

Put a Fruit Fly Trap In Your Bin

Most worm bins don't have the vertical clearance to allow for the funnel method described above.

In a bin like the Urban Worm Bag, you might opt for a shallow jar or Tupperware dish, again filled with vinegar or maybe even red wine as pictured!

Cover the jar tightly with cellophane and puncture the top of the cellophane several times with a toothpick. This too will attract fruit flies to the vinegar or wine but the inward facing punctures will make it damned hard for them leave!

Consider these Non-Toxic Fruit Fly Traps from Amazon

Suck up the Fruit Flies with a Vacuum

This is perfect in a bag-style vermicomposter like the Urban Worm Bag, Vermibag, or the Worm Inn.

Simply insert the wand of your vacuum cleaner through the top zipper, keeping the opening only as large as needed to get the wand in there.

Once you turn on the vacuum, leave it on for a couple minutes, ensuring that the wand isn't close enough to start sucking up bedding.

While I doubt you're going to count them, it wouldn't surprise me if you just removed hundreds of egg-laying fruit flies from your worm bin in a matter of seconds!

Summary: The Battle Against Fruit Flies Is Difficult, But Winnable

To paraphrase the words of ESPN's Dan Patrick, “you can't stop fruit flies. You can only hope to contain them.”

While I do have plenty of readers who don't express issues with fruit flies, worm bin owners who push their bins to the limit will at some point find that they've attracted the little buggers, like college guys to a kegger.

So if you've had luck preventing or eradicating fruit flies from your worm bin, I'm curious to know……what's been working for you?

Let me know in the comments below!