by Andreas Herrmann

Acetic acid works quite well, but where the proteins of the muscles have become hard due to denaturation, acetic acid will not relax specimens. In such cases, a chemical is needed which will break down the proteins. In Germany we use simulated gastric juice for this aim: 1% pepsin, 1% hydrochloric acid and 98% water. The solution (as well as the pepsin powder itself) should be stored at temperatures below 15 °C when not in use.

I use the same glass tubes (10 or 20 ml) as for killing specimens. Put a few beetles into a tube and fill it with pepsin solution. Then store in a warm place such as an airing cupboard or above a radiator (maybe at 30 or 40 °C) and leave for a few days. If the beetles are still stiff after a few days, they can be left for up to a few weeks but I rarely have to do this. More time is needed for larger beetles, or at lower temperatures. Discard the pepsin solution afterwards: it can only be used once.


  1. johan says:


    This seems an ideal solution but having spent most of the morning phoning round and googling I can’t seem to get hold of pepsin powder. This would help me a lot as I do photography of specimens – see the link.

    I am not much of a chemist – can anyone confirm that digestive aid vitamins containing pepsin and betaine HCL, dissolved in water, might have much the same effect?

    Many thanks for your time


  2. markgtelfer says:

    I recommend you ask Andreas Herrmann ( Please let me know the answer.

  3. Ian McClenaghan says:

    A long time ago a Japanese entomologist published in the AES bulletin that you could use the proteolytic enzyme in fig juice to relax insects. I have never tried it.

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