Are "giant" mealworms really sterile?

I have heard conflicting accounts of whether or not "giant" mealworms are truly sterile. I am talking about the larvae of "Tenebrio molitor" that is labeled as "giant", not "Zophobas morio" larvae, or superworms.

Some accounts state that such mealworms are actually given bran that is laced with growth inducing hormones, that in turn, force the mealworm to forgo pupating and to keep on growing and shedding their exoskeletons until they are about twice the size of an average mealworm. If they do somehow pupate, they will emerge as sterile adult beetles (which are the exact same size as normal, non hormone treated "Tenebrio molitor" adults), and no further generations will crop up.

However, I've also read that if they do pupate, and emerge as adult beetles, they will breed like normal adult "Tenebrio molitor" and their resulting offspring will either be of average size, or "giant" like their parents were (its not clear what size the offspring will actually be). I have read a few accounts of people who have gotten their "giants" to successfully reproduce, and the resulting offspring are also fertile and will continue the lifecycle and create further generations.

So, are the "giant" mealworms sterile or not? What is the actual truth?

If they aren't sterile, future generations won't be any larger than normal, as it is not possible for an acquired characteristic to be part of the parental genome.

I have successfully bred giants. The offspring are "normal". This colony is in its 3rd generation.

JZC said:

If they aren't sterile, future generations won't be any larger than normal, as it is not possible for an acquired characteristic to be part of the parental genome.

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I thought so. Thanks.

SamuraiSid said:

I have successfully bred giants. The offspring are "normal". This colony is in its 3rd generation.

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Ah, good to know. I have a "batch" of "giants" right now, that I bought without actually realizing it. I saw that they were "Tenebrio molitor" and stopped reading the label on the lid of the tub after that. Only after getting into the car and looking into the tub, and then actually reading the label on the tub's lid, did I realize that they were "giants". I am eager to see if they pupate and if so, how many offspring I'll get.

Do "giants" produce as many offspring as "regular" mealworms? Fewer? Or is the difference not really noticeable? I am interested to how "giants" became known as possibly being sterile in the first place.

Ive done three colonies from scratch. Each time I get a tub of 100 mealworms from the lps, but dont count them or use any for feeders. One of these colonies was giant mealies, the other two were regular. I never noticed any difference in the number of offspring.

I have bred these before , what i got is a few big larvaes , and many original mealworms.

I always thought these were two different species. o-o So how exactly are the giants achieved? Growth hormones for sure or does it just happen naturally?

Belle Fury said:

I always thought these were two different species. o-o So how exactly are the giants achieved? Growth hormones for sure or does it just happen naturally?

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While the reply is late, I still made it, as of now.

The "giant" mealworms are fed bran laced with special growth enhancing hormones which delay the mealworm from pupating and thus, it sheds it skin a few extra times and grows larger than it normally would.

I am happy to reply that my "giants" have successfully made it to adult hood. Whether or not they will produce young is still undetermined.

artchic528 said:

While the reply is late, I still made it, as of now.

The "giant" mealworms are fed bran laced with special growth enhancing hormones which delay the mealworm from pupating and thus, it sheds it skin a few extra times and grows larger than it normally would.

I am happy to reply that my "giants" have successfully made it to adult hood. Whether or not they will produce young is still undetermined.

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Same. They have eventually pupated and matured into adults, but I haven't gotten the to reproduce.

khil said:

Same. They have eventually pupated and matured into adults, but I haven't gotten the to reproduce.

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if you have a large number of beetles , you will have larvaes after a month , if you have a few you will get larvaes after 2-3 months. Theyre not as proliofic as the mealworms. I just harvest 2 batch of giants in my bin after 5 months.

I have been raising giant mealworms for a little over a year. I must have got lucky with mine because as you can see in the attached photo they do grow much larger than regular mealworms without chemicals. I didn’t use anything for my mealies but oats as substrate and I keep several fresh big chunks of potato in each bin. The worm on the left is a regular mealworm and the one on the right is a giant mealworm that has not been altered with chemicals but the parents of this offspring had been. I bought the starters from the pet store in a box of 100 a year ago and this is the results I have had.

Scaldwell63954 said:

I have been raising giant mealworms for a little over a year. I must have got lucky with mine because as you can see in the attached photo they do grow much larger than regular mealworms without chemicals. I didn’t use anything for my mealies but oats as substrate and I keep several fresh big chunks of potato in each bin. The worm on the left is a regular mealworm and the one on the right is a giant mealworm that has not been altered with chemicals but the parents of this offspring had been. I bought the starters from the pet store in a box of 100 a year ago and this is the results I have had.

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Awesome findings! I just found my first larva in my giant mealworm batch tonight. I found this thread a month or so ago since I was curious, and came back here to see what people experienced.

I'll be curious if mine also keep their size, or if they'll revert to normal sizes. I'm also curious to see if the offspring are still fertile as well. These ones had a lot more trouble and deformations with eclosing, and so there were a number of badly shaped adults, with a couple deaths. But it very well could also have been just their conditions or environment they had during this phase compared to my normals (which all turned to adults beautifully).

What I might consider trying is making a colony with half-half giants and normals. If they could interbreed, I don't think anything remarkable would happen, but it could help keep create some diversity at the very least lol. But it'd be cool if any particular characteristics would be inherited at all.