Killing jar
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A killing jar is a device used by entomologists to kill captured insects quickly, humanely and with minimal damage.
The jar, typically glass, must be able to be hermetically sealed and usually has a 0.5-1.5 inch layer of hardened plaster of paris on the bottom to absorb the killing agent.
Previously, potassium cyanide was used as an active ingredient; because of the obvious risks this is now usually considered obsolete. The potassium cyanide was put under the plaster of paris and slowly decomposed, giving off hydrogen cyanide fumes. Certain millipedes give off hydrogen cyanide as a defensive mechanism, and placing some species in a jar is sufficient to make a killing jar, although the millipede itself will eventually be killed by the fumes.
Ethyl acetate (fingernail polish remover), sprinkled on the bottom of a tightly sealing jar into which some plaster of paris has been poured and has hardened will provide effective results. If the jar is no longer effective it can be replenished with another few drops. It is important not to have fluid sloshing around in the jar or the insects will get sticky and hairy insects will get matted fur or lose hairs or wing scales (butterflies).