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Mealworms turning black and dying

Some of my mealworms are turning black and dying, is this normal? I would guess anytime you get a new batch of insects some are going to die. I have my temperature at 80 degree F and my humidity at 85%. I have them in wheat bran with some carrots. Just wondering if this is normal or am I doing something wrong. thanks



  • It's pretty normal for a newly received batch of mealworms to suffer a few casualties from transit, and there will always be a few that don't survive until pupation. It sounds like you have the conditions just right, so just pick out the dead ones and keep an eye on the situation - the rate of attrition should go down over time.

  • Cool, thanks for the info

  • Hi, I'm Alessandro, I'm from Italy and I'm a new member in this forum. I would to attach some pictures for show you the trouble: I breed my mealworms in my cellar, temperature is from 22° to 30°C, and humidity is quite hight, from 65 to 90%. I separate colonies in small plastic boxes (28x30 centimeter, in the pictures are more small) in wooden shelves. I feed my mealworm with dried bread, carrots, leaves cabbage and apple. I tried to not use any bran substrate; sometimes I feed them with bran in small quantities because in Italy bran is not cheap. My goal is to breed mealworms mostly with vegetable waste and dried bread waste. Every week I separe bugs by poop with a metal mesh. This is the fifth cycle. I have 2 problems: in every cycle there is a moment when suddenly little mealworms, before they become darken and then died (60% of dead). Lately I can see another thing: before to pupate, they die as if they were eaten by another insect. He eats their tail or their head and mealworms become dry and not dark. Mealworms die not everybody, but one box a time, and in some box mealworm don't die. The percentage of died is about 50% in every box. Sometimes I can see also paw of an other insect into the box (I thinks It's impossible taht are adult mealworm paw because adults can't fall in an other box). I can say that in my cellar there are some little spider and some little flies. Those flies are also in the bran bag All the mealworms eat some feed and they are bred in the same climatic conditions I want to thank you for your advices and I ask sorry for my english

    Attached some pictures with little flies, mealworm eaten ONE FLIES EATEN

  • Hi aleq, - I just read your message. There are probably 2 things giving you problems.

    1) - To prevent mealworms getting eaten regularly in your cellar you may have to design a screen cover to protect them. My guess is, as you mentioned, there are spiders eating your larvae.

    2) - When there is a large percentage of dying mealworms that has no easy explanation it may be from pathogenic fungus that got into them; the fungus growing over time is why problem not seen until late.This requires the bins being sanitized. I would then only breed beetles coming from the bin(s) where less % of larvae died & also not breed in just one bin in order to see which population does best for you.

    There are some mealworm larvae/pupae that get eaten by other mealworm larvae. This does not sound like your main problem.

    About feeding them:

    You can feed mealworm larvae in vegetable waste if give them carbohydrate, like old bread. I press out vegatable juice waste before put it on top of my carbohydrate (bran). I do not mix everything up for them & do not spread the vegetable waste all over the top of the bran.

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