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Hi all,
What do you think is the best way to kill a fly? There are some many.. freeze it, use ethyl acenet, put in ethanol?

What do you say?

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Depends what you will do with the fly but freezing is the easiest and involves no chemicals so I usually recommend it to novices. I'd only suggest Ethanol if you were collecting into traps or were collecting in the tropics where mould might be a problem. Ethyl acetate is the preferred method for killing prior to setting and mounting because specimens remain soft and easy to manipulate - but chemicals like this are a little dangerous so they carry with them certain responsibilities, such as keeping away from children and animals etc. :)

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I use four methods, depending on the fly and conditions. I do usually collect flies alive in small tubes and containers topped with pieces of porous foam. Once back home, I kill what I want to keep by one of the following methods.
Freezing is the easiest method, but not always available. As a backup I carry a small bottle of ethyl acetate. A few drops of ea. in a well-sealed ziploc bag will kill the 'tubed' flies in half an hour or so. For the very largest flies I carry a cyanide killing jar. Dangerous stuff... The few Nematocera I take go directly into ethanol.

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Thanks for the answers,
What about letting them die by themselves? Sometimes I collect live one and put them in a tube. They usally die there if left alone within 1-2 days is it very different from dieing in the freezer?

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The longer the fly is alive, the more it will damage itself and the quality of the specimen will degrade - lost bristles, torn wings etc. If the specimen is known to be freshly emerged then it is sometimes useful to leave it for some days to burn up the fat reserves but in most cases I would freeze them as soon as possible to preserve them in the best possible condition :)

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Cyanide:o I don't think I would ever contemplate carrying this or even having it anywhere near me. Strictly for the brave. For larger flies I just give them a bigger dose of ethyl-acetate, in a smallish tube. It always seems to work.

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No one has mentioned using crushed laurel leaves. Collect the leaves in April/May(only the young newly emerged leaves will do) and put them through a mincer. When the two layers of the leaves combine, they will give off weak cyanide gas (harmless to humans) but kills flies quickly. The crushed leaves will last from 6-12 months in the bottom of a large jar, or you can put them in the bottom of a small tube under wadding, where they won't last so long. The flies remain relaxed for 2-3 days, and I never pin them straight away. Also no mould will grow. This method was used by the Victorians, also famous dipterists such as J.E. Collin. And it is completely free!;)

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On the upside, cyanide has a very pleasant smell :D

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Why? A very nice thing! Especially if you need to have a large series for DNA and do not want to anesthesize every next of the 200 flies in the net with the carbon dioxyde before you decide if to pin it or to put in the tube with the alcohol. The only caution: do not open your killing jar in the tent; just in the open air not to be poisoned (it works exactly like carbon monoxyde!).

The other minus is that some insects like many weevils are absolutely resistant to cyanides...

And the last, - cyanide is very unstable; it evaporates as HCN very fast, so you must keep with you 2-3 eppendorf's tubes with 2 lethal doses each during the one-month trip. And I am not sure if you can manage to bring either EA or KCN aboard with you when fly somewhere by plane, even in your luggage... :(

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Some people like myself do not feel it smells at all! Just a headache...

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Hmm? If Finland cyanide is traditionally sold (with special permission by entomologist's societes) in ready-made killing jars. A gram of solid potassium cyanide is embedded in a thick layer of plaster, which keeps it from evaporating very fast and provides an extra security barrier. Once activated by a drop of water, such a jar lasts for years: I'm still using my first one bought in 2004.

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All this fuzzzz... freezing, okay. But nobody I know takes a freezer on a holiday... And forget the dangerous version of Cyanide; IF they catch you at the airport, you will need a damn good excuse not to land in jail.
So, use ethylacetate. But don't buy the expensive version, the lab-jars.
Just buy simple nailpolish-remover, containing ethylacetate (so NOT based on alcohol, the other version; read the contents carefully). This stuff is very cheap and without questions carried in your luggage (NOT handluggage though :o ).

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Yeah, trying to smuggle cyanides aboard a plane is definitely a major no-no :D

Personally I have simply poured the small amount is ethylacetate needed for a short trip into an empty plastic bottle of mosquito repellent.