In which PCC(E) tells people how to get rid of fruit flies

April 7, 2021 • 2:00 pm

This is not the first time I’ve been asked “how to get rid of fruit flies,” but this time it’s by a reporter for Chicago Magazine in the article below.

The first thing I had to ask when they queried me, was “what kind of ‘fruit flies’ are you talking about?” For the true fruit flies, the tephritids that endanger California’s fruit industry (that’s why you get inspected at the state border), aren’t a problem to homeowners.

What the reporter was asking me about was what geneticists call “fruit flies” but are better known to entomologists as “vinegar flies”. These are in the sister family Drosophilidae, and are the familiar Drosophila used in the lab. When you see little yellow flies buzzing around your fruit bowl, they are drosophilids, most likely Drosophila melanogaster or D. simulans.

And Drosophila are harmless, except to winemakers, and only because they’re attracted to the smell of alcohol and fly into the wine vats to die a happy death. (Flies love the smell of alcohol, as it denotes their real love, rotting fruit, in which they lay eggs.) Winemakers use pyrethrins, a fairly harmless pesticide derived from chrysanthemums, to control them.

If you see Drosophila buzzing around your fruit bowl or a glass of beer, don’t kill them, just shoo them away. They shouldn’t be breeding in your house unless you have a bunch of rotting fruit that’s sitting around for 12 days or so—and who has that?

(When I lived in Davis, I was called by a bar in Sacramento that really did have a Drosophila problem. A quick investigation showed that there was a huge bin of leftover, rotting lemons and limes from the bartender behind the building, and that was the source of the flies. For solving that problem, I got free drinks!)

But a reporter from Chicago Magazine was interested in how to get rid of them, along with three other “problems”: hiccups, alley rats, and hangovers. Somehow I was picked to be the fruit fly expert, and here’s my answer (click on the screenshots below to see the others, each with a different expert:

Well, this is advice for those with dipteraphobia. If you see fruit flies, just gently shoo them outside!

46 thoughts on “In which PCC(E) tells people how to get rid of fruit flies

  1. “They shouldn’t be breeding in your house unless you have a bunch of rotting fruit that’s sitting around for 12 days or so—and who has that?”

    If someone DOES have it, I hope they aren’t planning to eat it!

    1. My parents…they are constantly fighting fruit flies. Two people who haven’t been able to adjust to a family of two rather than six. Plus, there is the added attraction of a kegerator. Fruit flies, like brothers-in-law, are frequently found wherever the beer is. 🍺

  2. We get annoying little flies that we thought were fruit flies, but probably not, around our house plants. They appear to live and breed in the potting soil. We set sticky paper traps to control them. Any idea what these are? They seem common to a lot of people.

    1. Those are fungus gnats. They’re usually not a big problem, but an infestation can harm seedlings and smaller plants as their maggots eat fungus and small roots. If the plant is large, there won’t be any serious damage. There are insecticides (including organic types) that can control them. You drench the soil to kill the eggs and stop the lifecycle.

      1. I have had thousands of generations in flower pots indoors for years & took them to work where they annoyed colleagues! The males do the same wing flicks to attract females as other flies. The females are born fat & full of eggs & I do not think the adults live very long at all.

        1. My experience as well, Dom. I have a couple greenhouses, so I deal with them year-long (perhaps a lag in deep winter). When I sew, I cover. Once the seedlings have their first or second true leaf, I lift the covers, the gnats come in, and that’s that. No big problems. I collect and waste money on “carnivorous” plants, but they don’t do anything to stop fungus gnats…nor do sticky strips in my experience. The only way to stop the cycle is through the soil, knocking out eggs and larvae. I don’t worry about them though, wee dirt things. Aphids, scale and mites, I worry about those f’ers. Being an organic farmer demands diligence and daily observation. A tough two words to adhere by.

    2. Yup, we have them (and the sticky traps) – I’ll try to get WEIT reader Dom to identify them next time he is allowed to visit.

        1. At least you’ll have samples to identify. Btw, blame the resident vegan (though to be fair, she doesn’t eat them).

  3. Why not get a Pinguicula for your kitchen? Turn your fly infestation into a science lesson with carnivorous plants!

    I think you can buy them from California Carnivores. I have a couple of pots of Venus flytraps, but they don’t often eat flies. They are handy for disposing ticks that dare attach themselves to my person.

  4. ‘but are better known to entomologists as “vinegar flies” ‘ – Following today’s Hili, I wonder what the etymologists have to say?

    “For solving that problem, I got free drinks!” – and there I was, foolishly thinking that scientific knowledge was it’s own reward. Still, at least now we know why the Chicago Magazine didn’t come to our host for advice on hiccups or hangovers…! 😉

  5. I have a question for the expert. I got this really nice (and very expensive) bottle of sherry vinegar and it came with a handy pouring spigot. What I didn’t realize, the spigot created a perfect vinegar fly trap! So one day last Summer I saw a bunch of flies hovering around the vinegar bottle, and then to my dismay, I saw there were at least 15 or 20 dead flies floating on the surface. I threw it out.

    So my question is: could I have just filtered out the flies and kept using the vinegar? Or could dead fruit flies actually spoil vinegar? I did purchase a new bottle, and this time, I didn’t use the spigot, so fly-problem solved. But I’ve always wondered if I wasted perfectly good bottle vinegar.

    1. Well, they would disintegrate and you’d have fly bits floating in your vinegar. I suspect you could filter them out and you’d be all right, but don’t count on my medical advice!

  6. Factoids I learned while working on alcohol dehydrogenase (ADH), a key enzyme for detoxifying ethanol. D. melanogaster has high levels of ADH and high tolerance for ethanol (up to about 12% as I recall) while its sibling species, D. simulans, has much lower levels of ADH and is killed by ethanol at modest doses. A corollary: collect inside a winery around the fermentation vats and you get mostly melanogaster. Go out into the vineyards and you get more simulans. Oh, and an alternative fly trap: a shallow dish with a mixture of ethanol and acetic acid (or vodka and vinegar). Flies are strongly attracted by the smell and the mixture has low surface tension so they are liable to slip and be engulfed.
    P.S. I can’t figure out how to do Italics for species names.

    1. For italics, you turn them on by using a less-than symbol , a letter i, and a greater-than symbol. At the end of the word(s) you want to italicize, you turn them off using a less-than symbol, a backslash / , another letter i and a greater-than symbol. It’s made tricky to explain because if I try to use the less-than or greater-than symbols in this comment WordPress won’t show them.

      You can see the symbols here:

      1. Maybe it should be “pissed as a gnat” not “pissed as a newt” and it’s all been another entomology /etymology mix up?!

  7. I just wonder if there might be more stories under the category “things scientists have done for free drinks”?

  8. Just shoo them away. Good answer. Why kill something that lives such a short life anyway and does you no harm.

    1. Which used to be one of the popular tests for translation programs – try it into your language of choice!
      Google Translate into Japanese says:
      which renders back into English literally as the original English text, but has the meaning
      Time flies as an arrow flies (which is not bad for “time (N) flies (V) like an arrow”)
      Fruit flies as a banana flies (“fruit (N) flies (V) in the same way as a banana (N) flies (V)”)
      The idea of “fruit flies” (N) has vanished, as has the joke.

  9. I did not know Jerry when he was a graduate student, but rumor has it he use to release the extra flies from his experiments rather than kill them. Such a kind heart.

  10. In my much missed former life of pushing flies, this method is what we did. Generally we would always have a few traps running at a time. When the loose flies were pretty numerous, there would also be many of the smarter ones milling about the bottle and cone, not going in.
    There ought to be a cartoon about this sort of thing.

    Btw a beer bottle with a little left-over in it also works well as bait.

  11. A quick investigation showed that there was a huge bin of leftover, rotting lemons and limes from the bartender behind the building, and that was the source of the flies. For solving that problem, I got free drinks!

    What’d the bartender get?

    Prolly not a promotion or a raise, I’m guessing.

  12. There is one species in the vinegar fly group that causes harm to fruit growers, particularly in California, Drosophila suzukii. It’s the only known species in the genus to lay eggs in ripe or ripening fruit, causing spoilage. It’s also known as the spotted wing drosophila, though only males have spots on the wings.

  13. I’m always late to these discussions so rarely post.

    I’m a homebrewer and make mead, cider, and beer. My wine was meh, so I don’t bother with it. The fruit flies have acetobacter, which facilitates turning ethanol into other things, mostly vinegar. Vapor locks are very important.

    I’ve always used fly strips to control them. They work just dandy, but one day, we came home and found that our new rescue cat, Yoshimi, decided to do battle with the fly strip. It’s hard to say who one. I have pictures but there doesn’t seem to be a way to post them.

  14. I did not have rotting fruit in my kitchen but in my backyard, I had a loquat tree (I live in Charleston SC). My advice–NEVER have a loquat tree on your property. They are beautiful, with shiny leaves and yellow fruit but they are the dirtiest trees on a property. They shed leaves year round, copious feathery seed complexes in the winter (!) and bounteous fruit in the spring/summer, all of which is impossible to keep cleared. Fruit flies abound. They enter with you through the door and live in the kitchen. So many vinegar traps tried. BAD LOQUAT!

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