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Why does the mealworm larvae turn black after death?

Hello everyone,

I have been breeding mealworms since almost a year now, and there is one question I keep asking myself, and could not find any answer online.

Why does the mealworm larvae turn black after death?

I kill them by freezing, or boiling. I found out that the boiling make them turn black, and freezing doesn't.

How do you prevent the darkening, when boiling them? Are they still safe to eat once black? Why exactly are they turning black? Oxidation? stomach explosion?

If you have some studies I could read, I would be glad!

Thank you for reading me :)


  • Hi Ozee, Are they all turning black? I wash my larvae, try to get rid of as much bran/carrot pulp as practical, pick out any that seem to be floating dead/damaged/blackening & then put them in already boiling water. They get poured out into a strainer for plucking out any unusual ones that passed 1st culling & otherwise they hold natural coloration.

    You observe freezing retains proper coloration so I assume you've quality control. Consider a trial using distilled water for boiling some larvae on the slim possibility your usual water is reacting in some way with either/or the metal/exoskeleton. I use reverse osmosis water because then put my boiled larvae into whey for storage & my tap water is quite high in dissolved solids. You probably could switch to bottled water if the distilled water trial makes a difference.

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