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Comment by adriand | Hacker News Reader

The best method is to put a bit of fruit peel and some beer or wine or vinegar at the bottom of a glass (e.g. a pint glass) and then fashion a cone out of paper, where the wide end of the cone is the same size as the mouth of the glass. Cut the pointy end so it’s a few millimeters wide. Insert pointy end first, and tape the wide end of the cone to the brim of the glass, forming a seal. Flies will enter the glass via the opening in the point of the cone, and will be unable to leave. This will collect huge numbers of them with zero maintenance.

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As described in the sibling comment, a glass with a fifth of vinegar, same amount of water, and a drop of dish soap will do the trick fine. No craftsmanship needed. The flies drop instantly when they touch the liquid.

Most people cover the glass with some cling film and punch a few holes through, but it will work fine without. The main advantage of the film is that the liquid won't evaporate away, and the trap will be good for a couple of weeks.

> The flies drop instantly when they touch the liquid.

To be slightly more specific, the soap changes the surface-tension of the liquid, causing it to, er, schlorp onto the insect in a way it does not expect.

That reminds me of JBS Haldane's classic essay "On Being The Right Size":

> An insect, therefore, is not afraid of gravity [...] But there is a force which is as formidable to an insect as gravitation to a mammal. This is surface tension. [...]

> An insect going for a drink is in a great danger as man leaning out over a precipice in search of food. If it once falls into the grip of the surface tension of the water -that is to say, gets wet - it is likely to remain so until it downs. A few insects, such as water-beetles, contrive to be unwettable; the majority keep well away from their drink by means of a long proboscis.

Can confirm. I have one constantly in my kitchen and it works great. Flies don’t seem to mind that I constantly dilute it by adding water to make more foam.

This is awesome and you feel powerful vengeance until you accidentally slip the paper cone a bit on disposal and a hundred fruit flies escape at once.

Vinegar - slosh around a bit and take most or all of them out.

Yes, I can confirm this works very well. Best, I don't know the alternatives; this one works though.

I saw the other day on Thingiverse a fruit fly trap. Example: [1] (it wasn't this one, and there are many other ones, but this one resembles the looks of the paper version). But I think its OK to make such a trap a few times a year during summer (when they're abundant here). You also wanna get rid of them ASAP, as they attract bigger flies.

[1] https://www.thingiverse.com/thing:3032998

Ooh, maybe this is the answer to my housefly mystery. We have tons of flies in the house, more than could have gotten in from outside, so they must have found a good source. The thing is, we did an exhaustive check and there is nothing for them to access of ours… except now that you mentioned it I realize there are fruit flies around probably in random fruits we have in a few serving bowls. Hmmm

I've tried this several times and it's never been successful. I don't know what I'm doing wrong, but I'm glad you got it to work!

I mix some cider vinegar, some fruit juice or cider, and a drop of dish soap. I put that in a small jar. I get some plastic film and make a small hole in the middle of the plastic about the size of a pea. I place the plastic on the jar and secure with a rubber band.

Place that on the kitchen counter near where the flies congregate. They will follow the scent down the hole where they will be mostly trapped and if they touch the liquid, they will sink and drown as the soap removed the surface tension.

Or leave jam smeared plate in the dishwasher for a day with the doors cracked open. Then just close the door and start the program

For best effect, laugh maniacally as you hit the "ON" button.

I've had success with the same, though I've used foil with a couple of smaller (toothpick sized) holes.

Watch it. Either the bugs don't go in at all: you need better bait. Or there's a gap where they are getting back out: tape the gap. Or they are too clever, and find the hole in the tip of the cone. I've never seen that, but you could try making the cone deeper?

Buying a plant seems easier, and I'm definitely not crafty enough to build a fruit-peel beer cone glass and have it look good enough to display.

The flies are a worse display problem than the glass

Yes, they love a little wine in a glass wine just like many humans. I never had to fashion a funnel, but it sounds like a nice trap.

A CD makes a good template for this cone, and cereal boxes are just the right weight/flexibility.

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