Beneficial insects

Drosophila: Annoying but Useful Flies!

You’ve probably come across those annoying little flies in your kitchen. You know: they’re tiny and you don’t see them until you move the fruit dish, then a cloud flies over. Have you ever gotten one up your nose? I have… I wouldn’t recommend it!

And there it is, in the nose, the Drosophila melanogaster! Photo: Botaurus.

Rather than tell you how annoying they are in the home, I want to explain why drosophila are actually useful – even superheroes – to humans.

Uses in the Laboratory

Also known as fruit flies, Drosophila have a very important role in science, especially in the study of genetics. They have been used as models in laboratories since the 1900s. It is one of the few animals whose genome is completely known: each of the 13,000 or so genes of this fly is known to scientists and we know what they do.

Knowing that more than 75% of the genes involved in human diseases are also present in this species, it is a very good start to understand how they work and, eventually, to try to cure the diseases they cause. Several insights into the immune system, embryo development and chemical resistance have been gained from the Drosophila.

In order to achieve these results, individuals worthy of horror movies were “created” by activating or deactivating certain genes. Strange as it may seem, these laboratory experiments have led to the understanding of several genetic concepts useful in today’s medicine. So, drosophila, annoying in the kitchen, but still heroes in their own way, right?

This fly has legs instead of antennas. Photo: toony.
The fly on the left is normal and the one on the right has two thorax and therefore two more wings.

The Link Between Frankenstein and Tomatoes

Drosophila is small, lives about 30 days, and costs almost nothing to maintain, which makes it a good laboratory subject. In addition, it lays about 500 eggs in its lifetime, up to 35 per day: enough to never run out of guinea pigs! It’s also easy to have several generations since the reproductive cycle is only 10 days. So, if we do genetic testing, we can have three different generations… in only one month! And up to 25 in one year! Quite convenient if you want to see genetic repercussions in the descendants.

You’ll understand that the reasons scientists like them… are in fact the reasons we don’t like them. Just forget a banana on the counter and a few days later: poof! A cloud of flies!

Photo: Daniel Lloyd Blunk-Fernández sur Unsplash.

It’s perfectly normal (and infuriating, I know), but that’s their job in nature: to reproduce and feed on very ripe fruits and vegetables. They participate in the decomposition of organic matter and the recycling of nutrients in the soil. They’re not the only ones doing it, but they’re among the little workers who turn your table scraps into rich compost for the garden. Just make sure the plant is outside your home…not in your kitchen!

I gave my mom some tomatoes from my garden. A few days later, she calls me and asks me why my tomatoes are full of fruit flies, while her grocery store tomatoes, which are right next door on her counter, have none…

Can you guess why? Pesticides! Drosophila were naturally attracted to my tomatoes since they were not sprayed with repellents. The ripening stage may also have played a role since these little flies prefer their fruit very ripe.

Avoiding the Fly Factory: Prevention Is Better Than Cure

In addition to being small and very numerous, drosophila are amazing acrobats, they can fly backwards and even do loops. Don’t try to catch them one by one like bigger flies, you’ll go nuts before you see a result. Instead, use these simple ecological principles to get rid of them:

Drosophila have an incredibly keen sense of smell, they can detect rotting fruits and vegetables from several yards away. Knowing this, here is my home-made solution: put your fruits and vegetables in the refrigerator, in airtight containers, or in very thin nets. Don’t leave fruit peels, compost or dirty dishes lying around. A plate full of tomato sauce can serve as food and a place to lay eggs for those pesky flies, if they can’t do any better.

Think of everything: a dirty sponge, a sink with food scraps in the pipe, a vinegar bottle that doesn’t have a tight cap… These are all cozy nests where this little pest can procreate.: Photo: cottonbro studio.

Once all the good smells are gone, set up traps: narrow-mouthed bottles (like water bottles) with a little vinegar or alcohol. Personally, my best fly harvest was in the bottom of an apple cider bottle. I had left an inch of cider, and added a few drops of dish soap to remove surface tension from the water, as well as some apple peels.

There are also very effective traps on sale everywhere. Photo: Amazon.

It is important to keep in mind that traps are good, but in a kitchen full of fruit smells and dirty plates, drosophila have a choice and will not necessarily go into the trap. Traps used without having “secured” the kitchen are therefore not very useful.

I live in a small village with only one restaurant. I could drive 20 minutes on a Wednesday night to get some good pasta in town, but frankly, the easiest thing to do is to have a pizza delivered, even if it’s not the best!

But open a poké bol restaurant in my town and the medium pizza will meet its Waterloo!

Conclusion: I am a drosophila.

Remember, they don’t live more than a month. If you have properly eliminated the places where they can reproduce, you should be able to put your fruit back on the counter after that time… until the next invasion!

Inner Peace

You can also accept that there will be a few flies in your home. Living in the country, they’re everywhere outside and they get in through my screens in the summer. Fortunately, I have never had a large infestation. I tolerate the presence of a few, and I store my excess fresh produce (squash, onions, garlic, etc.) in the basement in a room where they don’t go.

They don’t do any damage, aren’t harmful to health, plants or anything else. Honestly, I have much more to lose by getting angry at them than by tolerating them…

What is your miracle recipe to put in the trap to catch those famous fruit flies: vinegar? Sweetened water? Wine? Apple pie!

Audrey Martel is a biologist who graduated from the University of Montreal. After more than ten years in the field of scientific animation, notably for Parks Canada and the Granby Zoo, she joined Nature Conservancy of Canada to take up new challenges in scientific writing. She then moved into marketing and joined Leo Studio. Full of life and always up for a giggle, or the discovery of a new edible plant, she never abandoned her love for nature and writes articles for both Nature sauvage and the Laidback Gardener.

2 comments on “Drosophila: Annoying but Useful Flies!

  1. The minute I walk in the door with fresh produce I wash it. I put fruits and veggies in a soapy bath in my kitchen sink, wash and rinse. Unwashed bananas can hatch eggs in minutes of walking in the door from the store.

  2. We don’t seem to get fruit flies all summer until peach season and then it is a free-for-all. Red wine vinegar or apple cider vinegar or regular vinegar (with a bit of sugar in it) in a cereal sized bowl, covered tightly with clear wrap. Use a skewer to poke holes in the clear wrap – works every time. For some reason they never climb out. You can move it around the kitchen, if needed. Love all of your articles.

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