fruit fly problem

Chris Jones jonesc at
Sun Dec 31 15:30:13 EST 1995

In article <4c2ii2$8e5 at>, Dave Borski
<dborski at> wrote:

>I have a problem with fruit flies in my home. At least I think that is 
>what they are.  They are dark brown and about the size of a gnat and seem 
>to like fruits and sweet things.  Where do they come from and how do I 
>get rid of them?  If this is not the right place to ask, sorry for the 

No, you've probably identified them correctly (though I think gnats are
smaller). Unless you keep a good food/egg-laying resource around, they'll
probably peter out on their own; if you want to get rid of them more
quickly, try using traps near wherever they seem to hang out:

Fruit flies are attracted to a number of odors, particularly fermenting
things. Beer, bread products, and vinegar (cider especially) are
particularly good (if you don't have any rotting fruit handy).

Traps commonly used in labs consist of a layer of attractant in the bottom
of a bottle, with a funnel inserted in the top. Flies go in but generally
can't get out because they *usually* don't want to fly much in an enclosed
space (or they just can't find the relatively small hole in the end of the
funnel) and so they tend to crawl upwards, which means they go up on the
bottle walls, but won't climb back down the funnel to get to the exit. Not
very bright, but that's true of some people I know too, so I won't throw
stones. Be sure that there is no gap between the funnel and bottle lip, or
(obviously) the flies will walk right back out again: try sealing with
Saran wrap or something (we use parafilm in the lab).

The only problem is that beer and vinegar have high enough surface tension
that the flies won't sink readily, and therefore don't drown until they're
very weak and/or old. If you're into experimenting, you might try adding a
little dish detergent to the liquid to try and reduce the surface tension,
or just "uncork" the bottle outside periodically.

Chris Jones (jonesc at

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