Often called “Fruit Flies”, but real fruit flies are something else, so “Vinegar Flies” avoids confusion

Pretty much every year, around tomato harvesting time, we get some problems with these. Mainly because we end up with a lot more tomatoes than we can eat kind of stacked up in the kitchen, and it only takes one of them getting infested by these gals to pretty much fill the kitchen with hundreds of tiny little flies. For some reason, this year they particularly liked to hang out on the potted orchid in the kitchen:

It doesn’t take long for them to build up serious numbers, either: if the temperature is right (about 82 degrees F), they can go from egg to flying adult in just 7 days! And a single female can lay a few thousand eggs in her lifetime!!

Anyway, these are obviously one of the species of Drosophila, just look at those red eyes.

They may or may not be the famous Drosophila melanogaster (I suspect not, although I don’t know enough to tell for sure) although they are certainly related. D. melanogaster are some of the most well-known and thoroughly-documented insects in the world, because they are heavily used in genetic studies (they are well suited for this type of research, because they are easy to raise, breed fast, and lay lots and lots and lots of eggs)[1]. And no, there’s no particular significance to my posting a picture of one’s behind here, other than the fact that so few of the pictures came out in focus, and this is one of them:

(They were tiny and easily startled, so getting close enough to focus on them without scaring them off was a bit of a challenge). Anyway, they are quite an annoyance when they infest a kitchen, they get everywhere in large numbers. Anything fruitlike attracts them, the juicier the better[2]. They particularly like tomatoes, especially when the skin has split, although they like watermelon rinds quite a lot, too. Like this one:

Given a choice, what they really seem to like is rotting fruit, particularly if it is rotten enough to get that vinegary smell (hence the name “vinegar flies”). They also like open glasses of wine or beer. Or vinegar.

Getting rid of them isn’t difficult, it just takes a bit of housecleaning and patience. The first thing is to get rid of whatever they are breeding in. This will usually be something like a bad spot in a tomato from outside, or something in a garbage can that hasn’t been emptied for a few days. Or, if you have small kids, a piece of fruit that was left or dropped somewhere inaccessible. Once this is gone, we use two ways to clear out the adult flies:

1) Bait them with a bowl of juicy fruit, like watermelon rinds, or a dish of wine vinegar, or a slice of overripe tomato, or anything along those lines. Once it is covered with flies, slowly creep up on them with a piece of plastic wrap, and cover the bowl with it (as long as you do it slowly, it won’t spook them). Then just put the bowl in the freezer overnight. Then take it out of the freezer the next morning, let it thaw out, and catch the next batch of flies the next evening.

2) Go around the kitchen a few times with one of those little hand vacuum cleaners, and suck them up. They are delicate enough that the banging around they get in the vacuum cleaner seems to kill them instantly.

There are probably innumerable variants on each of these, but I think you get the picture. In any case, once there is no place for them to lay eggs, the supply of new vinegar flies is stopped and the adults all die off in a few weeks

We’ve actually considered raising them on purpose, for feeding to small predatory arthropods like spiders or newly-hatched praying mantises. Jumping spiders in particular evidently like them, I’ve been reading that in the wild, jumping spiders are the primary predators of vinegar flies. The only thing is that they are a bit hard to catch without squashing them, we’d probably need an Aspirator for this. Which would also be really handy for catching cricket nymphs. Maybe we should get an aspirator just on general principles . . .

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[1] While they are well-suited for lab work, they were not originally uniquely well-suited for lab work; I am sure that there are any number of other animal species that probably would have worked just as well. But, these thing kind of go into a runaway situation. When Charles Woodworth first proposed using Drosophila in laboratory genetic studies, they were perfectly fine, but he could just has easily have started with something else. But, after the first few studies were done using them, they suddenly developed a particular advantage: there was now a body of knowledge about their genetics. That body of knowledge, experience, and development of multiple strains with known mutations has made them more and more valuable, because now when a researcher works with them, the work builds on all this previous experience. If they tried switching to another species, then they would have to pretty much start from scratch, rediscovering a lot of things that are already known about Drosophila. So, now that they have been used for so long, it is almost impossible to not use Drosophila for genetics work.

[2] The joke goes, “Time flies like an arrow, and fruit flies like a banana”, but they actually like other stuff better than bananas. Unless you let the banana go all the way to mush, then it gets liquid enough that they are attracted to it.