What liquid attracts fruit flies?

by Barb Ogg, Extension Educator

If you bring garden produce into your kitchen, you may get fruit flies. Fruit flies are tiny, honey-colored flies with reddish eyes. They breed in overly ripe vegetables and fruit.

Once inside, fruit flies will emerge from your vegetables and will lay eggs on fruit on the counter, in food debris in your garbage disposal or garbage can. They can also breed in a rotted potato or onion. Do you recycle cans? Liquid from pop, beer or wine can produce fruit flies.

Fruit flies are attracted to processes associated with fermentation and breed in decaying fruits and vegetables. In the fermentation process, yeasts act on sugars, producing alcohol and carbon dioxide. Researchers at University of California-Berkeley found fruit flies are actually attracted to the carbon dioxide (CO 2 ) released during the fermentation process, not the alcohol.

The key to managing fruit flies is to locate and eliminate breeding sources. Once you do this, it can still take a couple weeks to get rid of all the flies that will eventually die a natural death. To speed this up, try using a simple, inexpensive fruit fly trap. What attractant should you use? We know fermenting liquids will attract fruit flies, but most of us don't want to brew beer or ferment fruit in our kitchen just to get rid of flies. Instead, use yeast.

Simple Yeast Trap for Fruit Flies

1. Use a one-pint glass jar. Add 1/4 - 1/3 cup of warm (not boiling) water. Sprinkle a package of activated dry yeast over the water. Add one teaspoon of sugar to activate the yeast. Swirl the yeast liquid. In a few minutes, the sugar will cause the yeast to foam and expand and start producing CO 2 .

2. Take a small plastic bag (like a sandwich Baggie®) and place over the mouth of the jar with one corner reaching into the jar.

3. Poke a small hole (no more than 1/8-inch diameter) in the corner of the bag with a pencil.

4. Secure the bag around the rim with a rubber band or canning ring.

This trap will immediately begin attracting flies, which will crawl down the plastic, through the hole and into the jar. Once captured, most of them will be unable to find their way back out. Fruit flies tend to be active during the daytime, so make sure your trap is on the counter during the day.

Some captured female fruit flies will lay eggs, which hatch into maggots. These maggots will feed on the yeast liquid in the bottom of the jar. At 77 degrees F, it will take about one week for fruit flies to develop through three maggot stages, pupate and produce a second generation of adult flies. (At 70 degrees F, this life cycle will take about 10 days.) Once they are mature, the maggots will crawl up the inside of the jar to pupate. At this point, it will take less than a day for them to emerge.

Most of these second generation flies will be unable to find their way out of the trap, but to prevent any escapees, you may want to dump the contents of the yeast trap and clean out the jar to kill the larvae. Dumping the trap one week after you initially made the trap should be soon enough. If you dump the contents in the sink, flush the pipe with water for a minute to make sure larvae are flushed into the sewer system. If you still have fruit flies, you'll need to make a new yeast trap.

If the flies you have don't seem to be interested in the trap, you may have a different species of fly and will need to consult with someone (like your local extension educator) who can identify your flies.

People who have used these traps have been amazed at how fast they work.

The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office

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We don’t know where the fruit flies came from—they just showed up one night. Maybe some stowaway fruit fly eggs arrived on a bunch of bananas from the grocery store. Or maybe it was a bad idea to let fruit salad sit on the counter while we had a bonfire in the backyard. Or maybe I neglected to empty our compost bucket for a little too long and some of those awful pests with their sense-of-smell superpowers shimmied their way through a screen.

However they got into our house, we wanted them out. Fast.

Then I noticed a pin on my ever-helpful Pinterest feed: Make a Homemade Fruit Fly Trap, it announced. So I did.

What Causes Fruit Flies, Anyway?

Long story short: fruit flies are attracted to ripened fruits and vegetables, which probably doesn’t come as a surprise. The surprising part, however, is how they travel into your home. Fruit flies are usually brought in by you. Yes, you! These little buggers linger on produce and are brought into your home when you unpack your grocery goodies.

Once they’ve snuck into your home, their breeding process begins (if it hasn’t started already). They breed almost as soon as they land—laying eggs underneath the surface of your precious produce. No matter where they breed, you’ll want to act fast. Female fruit flies can breed up to 500 eggs, which can hatch within a WEEK—eek!

Pro tip: Think throwing away infested produce is enough to get rid of these pests? Think again. Fruit flies can (and will) continue breeding within trash bags, drains and garbage disposals. Be sure to throw away rotten produce before your little friends move in for good.

My anti-fruit fly campaign became a bit of an obsession. I didn’t just want to make one type of trap, I wanted to try a bunch so I could end the invasion once and for all. I Googled “homemade fruit fly traps” and felt slightly relieved to discover a long list of folk remedies. Obviously, I wasn’t the only person to fail at keeping fruit flies at bay. I put the five most popular recipes—all of which use common household items—to the test. I’d noticed most of the fruit flies were hanging out near the vinegars in my pantry (did you know vinegar lasts forever?), so I cleared a spot for the traps on the shelf and let them do their thing for about 12 hours. Here’s how each trap fared.

The DIY Fruit Fly Traps

Trap 1: Rotten Fruit

Potential benefits: Inexpensive, proven fruit fly attractor, gives rotting fruit a new use

How to make it: Put some chopped, past-prime fruit in a bowl. Tightly cover the bowl with plastic wrap and secure with a rubber band. Using a toothpick, poke a few holes in the plastic. The holes should be large enough for fruit flies to crawl in but small enough to keep them from getting out.

My take: While I was preparing the other traps, fruit flies were already coming over to investigate this one. I was sure it was going to win.

Fruit flies captured: 0 (Seriously! I wish I had put up a pantry cam to find out what happened, but I can guess. Read on.)

Trap 2: Milk + Sugar + Dish Soap + Black Pepper

Potential benefits: Uses common household items, a good way to use up milk that’s close to expiring

How to make it: Combine 1/2 cup milk with 2 teaspoons granulated sugar. Heat it on the stove or in the microwave, stirring occasionally, until the sugar dissolves. Stir in a squirt of dish soap (this makes the surface of the liquid somewhat sticky so the fruit flies can’t escape) and pour the mixture into a bowl. Crack black pepper over the top.

My take: This was the most frustrating trap to keep tabs on, because I couldn’t tell the difference between specks of black pepper and potential casualties. Luckily, when I dumped out the bowl the next morning, I could see the results.

Fruit flies captured: 3

Trap 3: Balsamic Vinegar + Red Wine Vinegar

Potential benefits: Quick to set up, easy cleanup

How to make it: Combine equal parts balsamic and red wine vinegar in a glass. Cover tightly with plastic wrap, secure with a rubber band and poke a few holes in the plastic (as with Trap No. 1).

My take: Fruit flies sure do like the vinegar bottles in my pantry, especially the balsamic. But for some reason, they weren’t attracted when it was served up in a glass.

Fruit flies captured: 0

Trap 4: Dish Soap + Apple Cider Vinegar + Hot Water

Potential benefits: Quick to set up, uses common household items, easy cleanup

How to make it: Squirt a little dish soap into a glass. Add apple cider vinegar until the glass is one-third full. Let your tap run until the water is steaming hot, then blast it into the glass so a thick layer of bubbles forms on top.

My take: I knew I was on to something as soon as I concocted this trap. The fruit flies that had been hovering around the rotten banana (Trap No. 1) buzzed right over. The bubbles dissipated quicker than I would have liked, so I had to keep adding more water to refresh the bubble layer. However, the fruit flies didn’t seem to mind when the vinegar became increasingly diluted.

Fruit flies captured: 18

Trap 5: Beer + Rotten Banana

Potential benefits: Gives rotting fruit a new use, a valid excuse to dump a beer you’re not a fan of

How to make it: Put a piece of rotten banana in a jar. Pour in enough beer to partially cover the banana. Grab a cone-shaped coffee filter and poke a small hole in the bottom. Set it on top of the jar, folding the paper over the edges of the jar to hold it in place. (You definitely don’t want to use these amazing local craft beers in your traps.)

My take: This turned out to be a sad waste of beer. When I removed the coffee filter the next morning, there were more living fruit flies than dead ones in this trap.

Fruit flies captured: 3 dead, 5 alive

The Results

Trap No. 4 won by a landslide! I was inordinately happy (gleeful, really) to see the death toll mounting each time I checked this trap during the day. But I also think Trap No. 5 has potential. If you’re curious about this method, add a squirt of dish soap to the beer and use the plastic wrap cover method from Trap No. 1. Maybe you’ll have more luck.

The Takeaways

Since that first test, I think I’ve perfected the winning trap. As you can see from the photo, I used a juice glass, which meant I had to refresh the bubbles a few times. Later, I tried it in a pint glass. Sure, it uses more vinegar, but the bubbles last much longer, making fruit fly killing a hands-off event.

I also tried this trap with two types of apple cider vinegar: the clear filtered stuff and the raw, unfiltered variety. The latter was definitely more effective, probably because it contains little bits of fermented apple. (Do you know the benefits of eating fermented foods?)

Since the experiment, I’ve kept a pint-size trap in my pantry (I also cleaned my vinegar bottles and have been faithfully taking out the compost). I’m happy to report I hardly ever see fruit flies anymore. But if and when they ever stage another invasion, I know what to do—and now, so do you.

How Can I Prevent Fruit Flies?

The easiest way to avoid a fruit fly catastrophe? Use up those ripe fruits and veggies! (Here are some great ideas for using up ripe bananas.) If you want to save your ripened produce for a few days longer, store them in the refrigerator to prevent any uninvited guests from breeding. When discarding inedible, overripe produce, make sure you throw away the trash ASAP.

Get rid of other pantry pests.

Originally Published: August 25, 2020