Dec 12

The Fruit Fly Experiement

Last week we had a slight fruit fly infestation.

We’ve had fruit flies before, but those were because of our across the hall neighbor, who, while a nice guy, has a tendency to work long hours and neglect to take out his garbage. The building manager told me how once she and the exterminator (who checks the building once a month) found our neighbor’s trash can positively teeming with fruit flies. Then my suspicions were confirmed when I witnessed a fruit fly buzz in from under our doorway.

This time, however, it was all our own fault.

MB was very excited one night to come home with free bananas. He doesn’t care so much about free or cheap stuff, but he knows I appreciate it. The only problem with the bananas was that we couldn’t eat them fast enough, which unfortunately attracted fruit flies.

We’ve had bananas before. They’ve drawn a few fruit flies, but as soon as we finished or threw the bananas away, the flies would be gone. However, this time, in combination with the bananas, we unthinkingly threw out some pear cores in an open garbage bag. One day I went to throw the bag away, only to be greeted by a swarm of fruit flies.


I got the bag in a large plastic one and tied it up, but not before a whole bunch more came zooming out. I threw out the bag and still hoped for the best. Maybe there weren’t as many as I thought, or maybe they’d just follow the garbage (or go into our neighbor’s apartment – just kidding, of course). But there were as many as I thought, they didn’t follow the garbage, and they didn’t go into our neighbor’s apartment.

They were in our place, and they were everywhere.

They were in the front hallway, the bathroom, and especially the kitchen. They constantly flew into our faces. We managed to kill a few, but that barely made a dent in the population.

Experiment #1: Fancy mosquito zapper plus fruit

MB had the idea to use this fancy mosquito zapper we got (in case you didn’t know, I’m paranoid about mosquitoes). It hasn’t been much use in attracting mosquitoes, but we thought we’d take a shot. MB put a pear core in the bottom of the zapper, and set it in the kitchen. The fruit definitely attracted the flies, but they ignored what’s supposed to kill them: the light and deadly fan. The next morning, the bottom was full of flies – which promptly flew out when MB opened it.

Experiment #2: Vinegar, dishwashing liquid, jar, plastic wrap

I did some research about fruit fly traps and found this one on Lifehacker. Encouraged by the comments, I got some apple cider vinegar and, following the directions, put a little in a couple of jars with a few drops of dishwashing liquid. I covered one jar with plastic wrap and one without since people seemed to say that both worked.

The flies ignored the jar with plastic and flew to the one without. I removed the plastic from the first jar, and more flies went there. However, none of them went in. They just hung out on the edge.

Someone on Facebook said that balsamic vinegar worked better for her, so I filled another with that. The flies were indeed attracted to it, but again they didn’t go in.

Experiment #3: Vinegar, dishwashing liquid, jar, funnel

This video from Chow suggests the funnel method.

I didn’t try it at first because I didn’t believe the flies wouldn’t be able to figure out how to fly back out of the funnel. But Experiment 2 wasn’t working.

I used balsamic vinegar in one jar and apple cider vinegar in the other. It took a while for the flies to go in, but they did, and I was amazed they couldn’t figure out how to get out. They would either hang at the end of the funnel or crawl up the side of the jar to the top, looking for a gap between funnel and jar.

I had taped the funnels to the edge of the jars pretty well, but what I had neglected to do was to tape the paper all the way up the open edge. At least one fly managed to wriggle its way out the untaped flap. After that I sealed that funnel right up.

All afternoon and evening, I obsessively checked on the jars. “Go in!” I’d mutter to the flies hanging out on the edge of the funnels. “Drown, you bastards!” I’d whisper to the ones still clinging mere centimeters above the surface of the liquid.

I let the jars sit out all night and for the whole next day.

The Verdict

There were a lot more flies in the apple cider vinegar jar than the balsamic. There were only about five in the balsamic (yes, I counted the corpses) and about 15 in the apple cider.

I thought we had lot more flies than about 20 so I refreshed the jars (both with the apple cider variety this time) and left them out for a night and day, but only one fly got trapped.

However, it seems the flies are almost all gone. I’ve noticed one or two flying around, but it’s nothing like before.

Now I know if, God forbid, this ever happens again, the apple cider vinegar funnel option is the way to go.