Help me understand fruit flies
September 8, 2011 12:34 PM   Subscribe

I've had a lot of fruit flies in my kitchen this summer. It seems impossible to get rid of them, so i've just learned to live with them. But I've been watching them, and now I'm curious about their behaviour and lifecycle.

I hope some entophiles can help me out with a few questions...

Fruit flies are famous for rapid procreation - so why is it so rare to see fruit fly larvae? (Once once did I ever see tiny white worms near some rotting fruit.)

Are fruit fly eggs visible to the naked eye?

Why are some small and light brown and others 3-4x larger and darker? (male/female? maturity?)

Why do they like to hang out on the mirror above my sink? (They don't seem to be fond of other glass surfaces.) They also love to sit on the black wire that holds a lamp that's also near the sink. Could be the moisture or scents from the drain, but they also love another hanging lamp cable that is over the table.

Why do fruit flies just hang around doing nothing? Are they just patiently waiting for some fruit to start rotting?

And... are there any definitive sources for in-depth information about insect behaviour?
posted by kamelhoecker to Science & Nature (23 answers total) 13 users marked this as a favorite
They probably like the areas near the sink because they're breeding in your pipes. I've always heard to pour bleach down the sink to get rid of a fruit fly infestation, and it's worked for me.
posted by something something at 12:41 PM on September 8, 2011 [4 favorites]

something something, I'd doubt they were breeding in the pipes. The larvae will need food, and the only way they'll get enough food is if the drain is constantly filled with food and you don't flush the children by running water.

Instead, I think they're using the sink as a source of water, which all organisms need (even types of adult insects that don't eat after maturing, AFAIK). Pouring bleach into their water would also kill them, especially if they can't smell/taste it.

The eggs & larva are tiny, but I've also wondered where the hell they are. From what I've heard, they live on the yeast growing on rotting fruit, not the fruit itself, but that doesn't solve the mystery.
posted by IAmBroom at 12:49 PM on September 8, 2011

Once a long time ago I had a fruit-fly infestation in my kitchen that wouldn't stop. Eventually I found out that my roommate had bought a bag of potatos and put it back under the sink and forgotten about it. Fruitflies had found it, and the thing was a mass of larvae.

The reason you haven't been seeing any larvae is that you haven't found the food source they're living off of.
posted by Chocolate Pickle at 12:51 PM on September 8, 2011 [1 favorite]

The larva are visible to the human eye, but the eggs are only about 0.5 mm long and 0.2 mm wide (PDF cite) so they would be very hard to see.
posted by exogenous at 12:55 PM on September 8, 2011

Ignore if you're enjoying the observations, but: You can get rid of them (or at least reduce their numbers) with a mix of cider vinegar and soap (or some variation with water and/or sugar). They are attracted to the vinegar and, if there's a little soap to break the surface tension, they will land, sink, and drown. See here or here for details.
posted by Mr.Know-it-some at 1:03 PM on September 8, 2011 [13 favorites]

Why do they like to hang out on the mirror above my sink? (They don't seem to be fond of other glass surfaces.)

Fruit flies hanging out on the mirror in the bathroom. This is interesting because we had some "fruit flies" with this aberrant behavior a few years ago. They were not attracted to apple cider traps, and they loved the mirrors in the dark bathroom. What worked was traps containing salsa. I don't know if they were juvenile drain flies (definitely weren't adults) or some other species, but I've always wondered what they were.
posted by crapmatic at 1:07 PM on September 8, 2011

Correction -- apple cider vinegar, not apple cider
posted by crapmatic at 1:08 PM on September 8, 2011

If you want to see fruit fly larvae, start composting. We have a pail that we use to transfer scraps to the pile outside, and the flies breed like crazy on it. If I'm lazy about taking it outside, you can see the little larvae crawling around the inside and all the small eggs that are stuck to the bucket. They're really hard to remove, a strong blast from the hose is not enough to get them off.
posted by backseatpilot at 1:23 PM on September 8, 2011

I've spent decades working with fruit flies in the laboratory, but am not an expert on their behaviour in the wild. These are (very) educated guesses rather than authoritative:

1) Because they're small and hard to see and likely inside the food that they are eating. A couple of flies buzzing around a room are really noticeable, but hundreds of larvae tucked away: not so much. You need to let things get nasty so there are thousands!

2) Yes, just about. They look like white, iridescent jellybeans, about as tiny as is possible for someone with good eyes to see. They have a couple of tube-like appendages on them; the mother likes to push the the eggs down into a soft surface when laying them, and the tubes help them breathe. Although they're easy to spot on Petri dish of grape jello where you know females have been laying, I would be very surprised if you were able to spot them on your fruit bowl.

3) Different species. There are many species of fruit fly. Males and females may also differ in colouring depending on the species

4) They're attracted to moisture; their scientific name, Drosophila, translates as "dew lover". Scents from the drain is another good guess. They also are drawn towards light, and tend to walk upwards on vertical surfaces.

5) I think they have pretty simple lives. I don't think they eat much (especially the males) (and they eat the yeast on the surface of fruit rather than the fruit itself). They spend a lot of time looking for love — there's some kind of communication going on in the way they move around, and when they get down to a courtship dance it's pretty cute, with the guys showing of their wings and all that. You can google "drosophila courtship" for pictures and racy videos.

6) There's decades of study out there, but mostly in academic journals. The most-studied species is Drosophila melanogaster, which is likely the smaller of the species you have.
posted by nowonmai at 1:40 PM on September 8, 2011 [19 favorites]

Some info here; other university entomolgy websites may be good too.
posted by TedW at 1:59 PM on September 8, 2011

I just did my master's on fruit fly olfaction, so I have some experience with fruit flies.

Fruit flies are famous for rapid procreation - so why is it so rare to see fruit fly larvae? (Once once did I ever see tiny white worms near some rotting fruit.)
-They may be growing up in your trash or your drains.

Are fruit fly eggs visible to the naked eye?
-Yes, but you will probably never see them unless you're in a lab setting, since they are very small and the media they're growing on is probably rough enough to disguise them.

Why are some small and light brown and others 3-4x larger and darker? (male/female? maturity?)
-Male fruit flies are smaller than females. But usually the difference isn't quite that big. Fruit flies come out of their pupae full-size, so it's not maturity. You probably have more than one species. Drosophila melanogaster is very common and what I worked with - I'd be willing to wager that that is one of them. The other may be Megaselia scalaris, which isn't really a fruit fly. They are a bit bigger than fruit flies, scuttle around, and have a nasty tendency to live in drains (and corpses!).

And... are there any definitive sources for in-depth information about insect behaviour?
-For this I would personally look to scientific journal articles. Alternatively, you could pick up an animal behavior book, which do usually mention insects. Some fun things to look into are the fruitless gene, communal spiders, flies that mimic spiders, insect nuptial gifts, fly boxing, lek-mating (really sucks to have flies decide your head is the perfect place to lek), and so many more things.
posted by Logic Sheep at 2:03 PM on September 8, 2011 [3 favorites]

I quit buying bananas a couple of years ago and since then I have not seen a fruit fly in my kitchen.
posted by Uncle Grumpy at 2:27 PM on September 8, 2011

Such awesome scientific answers! From science! I feel most humble tossing my own observations into the ring, being just a layperson, and one with a liberal arts degree, to boot. But anyway! It's my experience that fruit flies are never really a mystery. Just a question you haven't solved yet.

Do this:

1. Remove all possible food sources from where the flies can get to it. This includes all fresh fruit and vegetables: eat them all up, put them in the fridge, or do without for a while. All organic material (including stuff you wouldn't think of as food, like coffee grounds or the lid of a spaghetti sauce jar with some sauce on the bottom) MUST be removed, cleaned, or disposed of.

2. Tidy up the area, with a particularly sharp eye towards little bits of water. Wash all the dirty dishes in the sink, clean up all the coffee cups with a little bit of coffee in the bottom, empty the drip trays of any house plants, etc.

You should see a 95% reduction in the number of fruit flies. (I don't know where they go. Probably best not to think about it.) If you don't, then move on to Level 2: decontamination. Starting at the epicenter of the infection, leave no stone unturned. You are looking for something disgusting and overlooked - like Chocolate Pickle's bag of abandoned potatoes.

Fruit flies don't just show up out of nowhere. They're feeding and breeding in something. It's a pain in the ass, but the good news is, once you find it and clean it, your problem will vanish very quickly.

And I agree with Uncle Grumpy, bananas seem to be the worst offenders as far as fruit fly breeding grounds goes.
posted by ErikaB at 2:52 PM on September 8, 2011 [2 favorites] kind.
posted by DMelanogaster at 3:46 PM on September 8, 2011 [10 favorites]

Fruit flies can easily be trapped. put about 1/2 inch of cider vinegar in a glass. Make a cone out of a sheet of paper. Trim it so that it will fit in the glass but not touch the vinegar. Set it near where you're seeing the most flies. They will fly in, and won't be able to figure out how to get out.
Others are correct in saying that this problem won't stop until you track down the source. The most common problem is old produce.
posted by Gilbert at 3:50 PM on September 8, 2011 [1 favorite]

something something, I'd doubt they were breeding in the pipes. The larvae will need food, and the only way they'll get enough food is if the drain is constantly filled with food and you don't flush the children by running water.

A little googling will tell you that drains are a very popular breeding ground for all types of small flies.

OP, here's a good resource on the subject with tips on how to identify what type of fly you have, where they're coming from and how to get rid of them.
posted by MaryDellamorte at 4:11 PM on September 8, 2011

The reason you haven't been seeing any larvae is that you haven't found the food source they're living off of.

I worked in a restaurant that had a bad fruit fly infestation for a while. As the problem got worse, we introduced more and more onerous cleaning procedures to rid the place of possible food sources and breeding places.

We went over that place with a fine toothed comb every afternoon and night (racking up some wonderful overtime for yours truly in the process). Cans and bottles were rinsed immediately after coming back from the dining room, garbage cans and recycling bins were scrubbed with bleach daily, heck, we bleached everything we could. An exterminator sold us a special foaming cleanser that was to be sprayed down every drain in the place every night, which must have been good for him because the stuff cost about $12 per can, and was also used to wipe down underneath prep tables and other dark areas where they apparently love to live. Onions and potatoes that used to be left out were refrigerated. Every crumb, every drop, every night.

This went on for MONTHS. Employees were disgusted, I can only imagine what customers thought. Then one boring afternoon as I scrubbed the kitchen, I noticed the cove base behind the dish table was peeling away from the wall due to overspray, and what do you think I found behind it? Hundreds of flies and larvae and a virtual zoo of other creepy crawlies. A little bleach, hot water, gagging, and a few days later, all the flies were gone. All.

Less dramatically, I had some in my apartment for a few weeks, and given my experience did a lot of the same things, cleaning, storing everything in the fridge, etc. I finally got off my high horse though and just dumped some clorox down all my drains for a couple days and I'm fruit fly free once again.
posted by hafehd at 5:05 PM on September 8, 2011 [2 favorites]

After cleaning my kitchen thoroughly and removing all foods that might attract fruit flies, I filled my sink to the brim with scalding hot water and a cup of bleach and removed the stopper and let water drain. It made a HUGE difference. Water pipes, little bits of gunk in the disposal are all fodder food for fruit flies. If you have a double sink do this on both sides. On the disposal side, run disposal as the hot bleachy water drains.
posted by shoesietart at 5:07 PM on September 8, 2011 [2 favorites]

nthing the statement that bananas are the main culprit. But that isn't why I'm here. I was so happy to see this askme because it gives me an excuse to recommend one of my all time favorite books:

To Know A Fly

A giddy little science book, more than fifty years old, it uses humor and cartoons to share the joy of science and the scientific method. But that doesn't do it justice. This book is fun! It was required reading in my college freshman biology class, and I've always tried to have a copy on hand since then-- I must have given away a dozen of them over the years. A short funny book that will teach you about research and flies and a whole bunch of other stuff. I envy people who now have the chance to read it for the first time.
posted by seasparrow at 8:51 PM on September 8, 2011

I have found it very satisfying to hang Fly Ribbon traps in the past, when I've had fruit fly issues. Of course, the more effective it is, the nastier it looks, but that's all part of their old world charm.
posted by mumkin at 9:39 PM on September 8, 2011

Seconding the fruit fly trap mentioned by Gilbert. It really does work quite well. I've had better luck with it in the past than the vinegar + soap method. You don't even need to make a cone with a sheet of paper if you have a funnel--just place the funnel in the glass. It's my favorite kind of solution: elegant, effective, and requiring of no effort.
posted by dephlogisticated at 9:55 PM on September 8, 2011

Thirding the cone method. Red wine or grape juice with a little vodka works really well. Flush the liquid when you're done. You'll still need to find the source of the infestation (keep in mind that flies are just as happy to eat rotting fruit out of the trash as on the counter, so take the trash out!), but it'll knock down the number of adults.
posted by maryr at 10:05 PM on September 8, 2011

Note: I learned the cone + red wine method when I worked in a Drosophila lab. They're an awesome model organism, except for the part where you can't freeze them and have to pass stocks forever.
posted by maryr at 10:06 PM on September 8, 2011

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