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Mealworm health issues

Several of my mealworms appear to have clumps of excrement stuck on the tip of their tail, to me they appear to me constipated, is this normal or is there concern that something is wrong with the mealworm environment?


  • I have also been replacing the vegetable every day at the same time as looking for pupae, and dead ones. I have noticed some of the mealworms that have the excrement on their tail act like they can wiggle but not crawl, are they pupating? Every day of shifting around the bran for pupa, I end up finding a few dead ones, is this normal to expect a few days after their arrival? Could I have shaken them too much when trying to sift out bran?

  • Hi Nukedpenguin, - You are currently rearing mealworms that grew up conditioned to temperature/humidity/feed/moisture parameters which are unknowable. In your care they are dealing with adapting to conditions at your place.

    Your "environment" is probably fine & mealworm lineage you generate will be more adapted in tune with what born into. Don't worry if they seem immobile but wiggle - pupae emergence is your most likely next event.

    Also you do not know how old the breeding beetles for the larvae you received. They were likely breeders of adults of several ages among them.

    Eggs from older breeding beetles hatch at a lower %. Although young "hatchlings" from both old & young parents grew similarly after awhile the larvae from older parents grow faster &, depending on variables like temperature, molt fewer times.

    Add to this situation the fact that colony density influences the pupae. One way this plays out is that mealworm larvae will use pupae as a convenient moisture source. Those victimized pupae looked sucked dry & even blacken, as opposed to appearing chewed apart.

    My surmise is that the larvae from old parent beetles are the most likely pupal moisture sucking culprits. The larvae which are still needing more molts (those from young parent beetles) are, in my opinion going to be busy with all that entails. Of course it may be the other way around on who might be a "vampire" larvae.

    Even replacing the moisture source daily doesn't mean all the larvae are going to bother going over to the vegetable. "Lazy" ones (fast grown, from old parent's eggs?)might be content to suck on a pupae at hand even if senses pick up on a vegetable "over yonder."

    Daily vegetable exchanges may be unnecessary in your set up; not to mention time/money consuming. Just for future reference the carbohydrate they eat(bran/grain)metabolizes into energy & water; so larvae don't readily die of "thirst".

    I don't get an image of larvae with anything "sticking" on their tail. Although no research describe it I think they will purge their guts, as reportedly black soldier fly larvae do, prior to pupation. In their pupal phase they are reprogramming their form/structures & it would be counter-productive to be diverting energy to digestion when they can't "poop" out waste that could shut their whole system down. What you describe may be a transitional feature of pre-pupal gut purging.

  • edited August 2014

    Thanks gringojay, for all the useful tidbits. I did find a pupa today that was sucked dry, those damn rascals... Can Tenebrio molitor develop as a pupa alone like superworms? I am asking because I have been keeping those "pre-pupas" in with the pupas to prevent them from being victimized by the opportunistic mealworms.

  • @Nukedpenguin - tenebrio molitor will develop through their pupal stage just fine alone or in groups, unlike the superworms that have to be kept alone. If you're having a lot of cannibalism you can easily pull out the pupae into a separate container as you notice them emerging.

    The thing you notice sticking to the tail may be the previous moult (i.e. the old exoskeleton skin)

  • Hello, newbie molitor consumer and proud farmer. Ordered 1,000 mealies about a month ago. Now have 140 adults of various ages. I've had about 180 pupa make the leap to baby-maker but I've culled about 40 because of deformities. I've seen a lot of deformed elytra and many that only partially converted and we're mutated. I did some research on genetic bottlenecking due to inbreading with no luck related to deformations. What just hit me was chemical contamination from plastic off gassing as I know various plastics can disrupt hormone functioning in humans. I'm wondering if anyone else has seen similar deformities? Also, are people introducing new genetic stock to their farms regularly? Thanks and keep buggin'!

  • edited September 2014

    Hey Bamboom, I purchased 1000 mealworms online several weeks ago, and most turned into beetles/pupa by now, except for like 150 mealworms that I ended up feeding to my chickens. I bought 2000 mealworms from a local supplier, but they had been in the fridge which was something I didn't know before taking the hour long trip. Anyway, the refrigerated ones were in a much poorer condition, but they were closer to pupating than the ones I bought online. I estimate that about 300 of the 2000 died, and only about 100 of the 1000 died. I noticed that in the batch of 2000, there were a lot of deformed larval mealworms that had recently molted, they have extra bubbly fin shaped protrusions near their head that are prone to busting and sticking to the wheat bran (My guess is that they tried to pupate but the refrigerator stunted the process, and the mealworms molted instead). Also I did have a dozen beetles that didn't manage to fluff their wings/wing covers correctly, so I gave them to the chickens, but I still have like 300 pupa that haven't hatched. I think that all organisms are subject to genetic bottlenecking so it can never hurt to have fresh genes. Thats why I'm keeping all the beetles from both suppliers together. So far I have about 25 healthy looking beetles.

  • NP - I have see the bubbly fin shaped protrusions but not very many and I haven't tracked what happened to the ones that had that feature develop - I'll pay more attention to the ones I see in the future.

    My swarm has pretty much stopped pupating and the remaining larvae seem to be just eating, pooping, getting bigger, and looking better (I pull out one dead every other day). There was a flush of pupa over the course of three weeks getting 10-15 every day right after I received them but now I get one every few days. The pupa I'm getting now seem to be larger and look very healthy while the ones earlier were clearly smaller and some weren't able to fully shed the last molt, particularly around the anterior thorax and head but some just barely cracked the shell.

    I seem to have about 300-400 left as larvae and they are active and seem happy. Based on the pupation pattern, I'm now wonder if there was a stress/environmental response to the move to my house that triggered early pupation and that may have contributed to deformities. We'll see how the second generation fares. I'm going to be getting another several thousand more to kickstart some serious production and I'll be getting them from several sources to stir the genes a bit.

  • @BamBoom - transit and sudden environmental change is definitely high stress for the insects, even mealworms which are particularly hardy. We've experienced and heard recounts of similar issues like large die-offs shortly after receiving batches of new insects. Hopefully the fortitude of the survivors pays off in the genetics of their offspring. Will by interesting to hear if you find any similar patterns when additional batches arrive.

  • Bamboom, I noticed too that there is a pupation gap in both of the batches I got, but I have just been feeding the rest of my mealworms to my chickens as they congregate in the edges of the tank (they are beefy looking). My population is about 400 right now and I just separated from the egg bran, my only trouble is figuring out how much wheat bran to use with them in their new container. I weighed 20 beetles, then divided the weight of all the beetles by the weight of 20 beetles and multiplied it by 20, allowing me find out that I had about 411 beetles.

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