Water Bags for Flies and Other Old-Fashioned Tricks: The Honest Tier List

Somewhere in America right now, a bag of water is hanging over a back door, catching the light, doing absolutely nothing. Maybe there's a penny in it. Maybe a scrap of foil. The person who hung it swears it works — the flies do seem thinner this week — and their neighbor is about to hang one too. It's the most-shared fly remedy on the internet, and it's folklore.

The trouble with fly advice online isn't that it's all wrong. It's that the proven method and the pure superstition get filmed the same way, with the same confident voice, so you can't tell which is which until you've wasted a summer. The same fog settles over bigger household pest fights — sorting out which bed bug remedies actually hold up means wading through the identical mix of solid method and confident nonsense. So here's the honest version: a receipts-first tier list of the old-fashioned tricks, ranked against what university entomology extension services actually document. This is for the ordinary household nuisance flies buzzing your kitchen — not a heavy infestation, a livestock setup, or flies tied to a septic or dead-animal problem, which are jobs for a licensed pro.

The honest tier list, in one glance

Before the explanations, here's where each remedy lands. The rest of the article shows the receipts.

• PROVEN: Exclusion (good screens, closed doors) + sanitation + finding and killing the breeding source.
• SITUATIONAL: The apple cider vinegar trap — real, but only for fruit flies, and only if you don't skip the dish soap.
• MILD / OVERHYPED: Herbs and essential oils — a flicker of evidence in a lab, not a fly-free kitchen.
• MYTH: The hanging water bag. It doesn't work.

Notice the pattern: the thing that actually works is the thing nobody makes a satisfying video about, and the thing everybody shares is the one at the bottom.

MYTH: the hanging water bag

WHAT it claims: A clear bag of water — sometimes with a penny, a marble, or foil — hung in a doorway supposedly scares flies off because they panic at their own giant, distorted reflection and won't fly under water.

WHY people believe it: This is a masterclass in observation bias. Fly numbers rise and fall on their own with the weather, the garbage schedule, and whatever's rotting in the yard. Hang a bag during any natural dip and your brain files it as cause and effect. Nobody remembers the weeks it did nothing.

What the evidence says: Extension entomologists put it plainly. Mississippi State University Extension lists the water-and-penny bag among the folk fixes and concludes, flatly, that "these homemade fixes just don't work". There's no credible mechanism behind it and no extension service that endorses it. A house fly's compound eyes don't process a water bag the way the folklore imagines.

LIMIT: If your bag "worked," you almost certainly did something else right at the same time — took out the trash, closed a window, cleared fallen fruit. Credit that, not the bag. Take the bag down; it's using up a doorway and a little of your dignity.

First, know your fly — this decides everything

Here's the mistake underneath most "my trap failed" stories: people run a fruit-fly method against house flies, or vice versa, and then blame themselves. These are different insects with different lives, and telling them apart is the fork in the whole road.

Fruit flies (also called vinegar or pomace flies) are tiny — Texas A&M AgriLife Extension puts them at about 1/8 inch long, usually with reddish eyes. They hover in slow little clouds over the fruit bowl, the recycling, the sink drain. Crucially, they breed indoors, in fermenting fruits and vegetables and the gunk inside drains.

House flies are the bigger, faster ones that dart in through an open door — and if they are the ones plaguing your kitchen, the step-by-step house-fly guide walks through identifying and clearing them. Per the same Texas A&M guide, they breed in decaying organic matter such as livestock feces and garbage, and "are generally not an important indoor pest unless doors or windows are poorly screened." They come in from outside; they rarely breed in your house.

So the identification isn't trivia — it's the diagnosis. Tiny slow flies at the fruit bowl mean an indoor source you can find and remove. Big fast flies at the window mean an outdoor source and a screening problem. As Texas A&M notes, "identifying the fly should be the first step in any control effort."

LIMIT: Other small flies wear similar disguises — fungus gnats from overwatered houseplants, drain flies from sink gunk. When in doubt, don't fixate on the insect; hunt for the moist, rotting thing it's breeding in.

SITUATIONAL: the apple cider vinegar trap — and why yours failed

WHAT it is: A small bowl of apple cider vinegar with a few drops of dish soap, left near where the little flies gather.

HOW it works: The vinegar smells like fermenting fruit and draws the flies in. The soap is the part everyone forgets, and it's the whole trick — it breaks the surface tension of the liquid so a landing fly sinks and drowns instead of skating across the top and buzzing off. Texas A&M AgriLife describes exactly this: "a plastic bowl containing an attractant, like apple cider vinegar, and a few drops of soap to drown flies that attempt to land on the solution."

WHY yours failed: Two reasons, and both are fixable. First — you left out the soap. Without it the vinegar has surface tension the fly can stand on, so it drinks and leaves. Second, and more common — you aimed it at the wrong fly. This trap catches fruit flies. Run it against house flies zipping the windows and it looks like a dud, because it is: they're not drawn to a bowl of vinegar and they're not breeding where you set it.

LIMIT: Even done right, a trap is a helper, not a cure. Iowa State University Extension is clear that a spray or trap is "only a temporary relief at best. Eradication will require eliminating the source." A trap thins the adults and helps you locate the hot spot. It will not, on its own, end the problem — and it won't touch house flies at all.

MILD / OVERHYPED: herbs and essential oils

WHAT people claim: A pot of basil or mint on the windowsill keeps the kitchen fly-free.

What the evidence actually shows: There's a real signal here, but it's smaller than the claim. In a controlled laboratory study, plant essential oils — eucalyptus, fennel, and sage — did repel adult house flies, with measurable repellency in a lab assay. That's genuine. But read the fine print the researchers themselves wrote: the effect came from concentrated oils, it was measured over a short window in glass flasks, and the authors state outright that "further field validation... [is] needed to understand their efficacy".

WHY the potted plant disappoints: A living basil plant on the sill isn't releasing anything close to a concentrated oil at a repellent dose. The lab result and the windowsill are two different things, and the honest gap between them is exactly why so many people say "the herbs did nothing." They're not imagining it. No extension service points to a potted herb as fly control; they point to screens and sanitation.

LIMIT and a real safety note: Concentration and reapplication would matter enormously if you tried to use oils seriously, and this is where caution earns its keep — several common essential oils are toxic to cats and dogs. Don't diffuse or dose oils around pets on the strength of a fly claim, and don't treat a herb garden as a barrier it was never proven to be.

PROVEN: exclusion, sanitation, and killing the breeding source

This is the tier that works, and it's boring, which is precisely why it doesn't go viral. It's the quiet backbone of nearly all effective do-it-yourself pest control, not just fly patrol. Three moves, in order.

1. Shut the door on them (exclusion)

House flies are mostly outdoor insects that wander in. Purdue University Extension frames the fix simply: "Keeping flies from entering homes involves using tight-fitting window screens and closing windows and doors." A torn screen or a propped door is, as NC State Extension puts it, an easy access point — flies pour through damaged or poorly-fitting screens. Patch the screens. This is a needle and a few dollars of mesh, and it does more than any bag or bowl.

2. Take away the buffet (sanitation)

Flies need a moist, rotting place to lay eggs. Deny it. NC State and Mississippi State both land on the same routine: seal food waste in trash bags in cans with tight-fitting lids, keep counters and drains clean, and — outdoors — clear fallen fruit and pick up pet waste. Mississippi State sums up the logic: if flies "don't have suitable breeding sites in and around your home, they won't be a huge problem."

3. Find the source — because the adults are only the symptom

This is the mindset shift that separates people who solve fly problems from people who swat forever. The flies you see are the visible end of a hidden nursery. House flies can go from egg to adult in as few as 7 to 10 days, which is why Purdue warns that "insecticides alone cannot be expected to rid premises of flies." You kill the adults, and a fresh batch matures within the week. UC IPM says it as directly as anyone: "Elimination of larval habitat is the preferred method of pest fly suppression," because chemicals "target adult flies, leaving immature developmental sites unchanged."

So follow the flies back. For fruit flies, that's a drain, forgotten produce, the sludge under the recycling bin, a damp mop. For house flies, it's outside — garbage, pet waste, compost. Find the wet, rotting thing and remove or clean it, and the flies stop coming because the factory closed.

LIMIT: Chemicals only ever supplement this — never replace it. If you do use an insecticide or a drain treatment, follow the product label to the letter, keep it off food surfaces and away from kids and pets, and heed NC State's caution against pesticide strips in occupied living spaces. Boiling water or drain treatments for fruit-fly larvae are effective but can scald you or damage pipes — go slow and follow directions.

Quick-reference summary table

Common mistakes recap

• Trusting the water bag. It's folklore; any improvement came from something else you did.
• Running a fruit-fly trap against house flies. Wrong tool, wrong fly — it will always look like a failure.
• Skipping the dish soap in the vinegar trap, so flies drink and fly off instead of drowning.
• Expecting a potted herb to do a concentrated oil's job. It won't.
• Swatting adults and calling it done. Adults are the symptom; unfound larvae are the cause.

FAQ

Does the water bag over the door really do anything?

No. Extension entomologists at Mississippi State list it among the folk remedies that simply don't work. If flies dropped off after you hung one, look for the real reason — a closed window, cleared trash, cooler weather.

My apple cider vinegar trap isn't catching anything. Why?

Two usual culprits: you left out the drop of dish soap (so flies float instead of drown), or you're targeting house flies, which the trap doesn't attract. It's built for fruit flies. Confirm which fly you have first.

Will basil or mint on the counter keep flies away?

Not reliably. The only solid evidence is lab repellency from concentrated essential oils, and the researchers say real-world validation is still needed. A living plant isn't a proven barrier — and keep in mind some oils are toxic to cats and dogs.

When should I stop DIY-ing and call a professional?

When the flies keep coming back despite good screens and sanitation, when the infestation is heavy, or when the source seems tied to a septic, sewage, or dead-animal problem you can't safely reach. Those are jobs for a licensed pest professional, not a bowl of vinegar.

The takeaway: the hanging water bag is folklore and the vinegar trap only catches fruit flies — the flies that actually leave are the ones whose door you shut, whose garbage you sealed, and whose hidden breeding source you found and cleaned out. Spend less. Live more. — The Thrifty Almanac