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Fruit flies


by Richard Jones

What's the point of having a compost heap unless it's to breed fruit flies. That's the way my entomologist's mind works. During the summer great clouds of them billowed up every time I dumped the kitchen waste.


Richard JonesWhat's the point of having a compost heap unless it's to breed fruit flies. That's the way my entomologist's mind works. During the summer great clouds of them billowed up every time I dumped the kitchen waste. They got in my eyes and hair and the odd really unfortunate one got into my mouth. Then they came indoors, having discovered open windows and open cat flap, and hung around the fruit bowl like miniature vultures or drowned in the chianti.

They're all gone now...or so I thought. In fact the heap is still pumping them out, except now they are so slow and quiet that they can barely get airborne. So with little else to look at, I turn my attention to these tiny little specks.

The trouble with identifying flies is that you usually have to examine individual bristles on individual legs. So it's no surprise that my key to Drosphila fruit flies is very keen on the number of hairs of the insect's thorax, the colour of its knees and the presence or absence of spurs on its back legs.

I must admit that it's been over 30 years since I last looked at a specimen of Drosophila down the microscope. That was the laboratory species Drosophila melanogaster, widely used around the world in all manner of genetic studies. It's the only species most people have heard of.

So I'm quite impressed when I discover that I actually have two other species living in my potato peelings and banana skins: D. immigrans and D. hydei. Both are apparently very common in 'decaying vegetable matter'. I'll remember that when I fish one out of a glass of red wine over the Christmas holiday.



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Gardeners' World Web User 30/12/2007 at 12:45

I have the same problem, fruit flies by the hundreds, is there anything I can do?

Gardeners' World Web User 31/12/2007 at 14:55

I once read that the addition of shredded newspaper stopped this happening. Worth a try.

Gardeners' World Web User 02/01/2008 at 09:21

Reply to Sheila - Although I'm no compost expert, I think the problem is too little 'brown' matter. That is, too much kitchen waste and not enough garden stuff. The flies are attracted by the aromatics of fruit and veg fermentation so more dead leaves, corrugated paper and prunings may help dilute the fruitiness of the decay.

Gardeners' World Web User 03/01/2008 at 18:51

Hi,I too last looked at a drosophila many decades ago, whilst studying A-level genetics at school! I remember grouping them by wing size, spots or no spots, colour etc. The poor things had 2 weeks of frenzied breeding and eating, only to be unceremoniously chucked out into the garden when we had stared at their offspring!!

I now run a gardening club at a secondary school, where the compost heap in the school garden is rotting away merrily. Whilst developing our wildlife education, we have discovered a simple way to deal with the flying visitors... we have put up a bat nesting box on a nearby wall, and our little fellas eat anything that moves. We have a pile of logs for our local hedgehog, who along with all the frogs who also live in the compost heap, help to keep our slugs on their toes (metaphorically!!) So...... maybe an answer to your chianti floaters might be getting a little help from the other widife. Good luck.

Gardeners' World Web User 29/01/2008 at 17:04

Having the compost crawling with fruit fly maggots brings other insect wildlife with it too. There are lots of predators, mainly beetles (adults and larvae, that feed on the Drosophila grubs. My favourites are the histerids, small (4-10mm) shiny black critters slightly flattened broad rounded globular with thick digging legs to pull through the slimy mess.

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