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Hello! Mostly I keep millipedes but I also enjoy keeping Gymnetis caseyi because they're so easy and pretty. I recently discovered about 30 larvae and pupal cells of a large scarab in a rotted tree in my yard. Not knowing how to ID the larvae, I set each larva up in its own enclosure filled with the wood in which i found them.
 
The first pupa has eclosed into a Hermit Flower Beetle, I'm pretty sure it's Osmoderma scabra due to the rough elytra. I love how this beetle looks and behaves!
 
It's hard to find detailed information online about Osmoderma husbandry, though every reference I find states that they are "very easy." :)
 
I thought I'd inquire with the brain trust here to see if anyone has any advice. Here's the setup I plan for the 20 larvae I have now:
 
- A single communal enclosure for all the grubs.
 
- A large tub with deep substrate of tightly packed, decomposed wood of the tree I found them in, with some decomposing hardwood leaves mixed in.
 
- Supplemental food of dog kibble and fruit offered at the surface.
 
- Keep the substrate damp but not wet.
 
- I'd go through the whole substrate every 6 months to separate out any pupal cells and move the batch into a new identical enclosure if the substrate is used up.
 
- Keep pupal cells in a separate enclosure for adults to eclose into, then feed them bananas and fruit juice, and hope they mate and lay eggs in there.
 
I say all this to see if anyone with experience raising this or a related genus might like to chime in to affirm or correct anything in my plan. I've discovered another well rotted tree on my property to investigate and I may collect another 10 larvae or so. Any thoughts or tips would be appreciated. Thanks!

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Hello! Mostly I keep millipedes but I also enjoy keeping Gymnetis caseyi because they're so easy and pretty. I recently discovered about 30 larvae and pupal cells of a large scarab in a rotted tree in my yard. Not knowing how to ID the larvae, I set each larva up in its own enclosure filled with the wood in which i found them.
 
The first pupa has eclosed into a Hermit Flower Beetle, I'm pretty sure it's Osmoderma scabra due to the rough elytra. I love how this beetle looks and behaves!

Yes - definitely Osmoderma scabra.  Along with O. eremicola, it's among the largest cetoniine scarabs found in the US.  Members of this genus also occur in Europe.
 
It's hard to find detailed information online about Osmoderma husbandry, though every reference I find states that they are "very easy." :)

Rather easy, yes.  I reared O. eremicola for some years, and never had any problems with them.
 
I thought I'd inquire with the brain trust here to see if anyone has any advice. Here's the setup I plan for the 20 larvae I have now:
 
- A single communal enclosure for all the grubs.
 
- A large tub with deep substrate of tightly packed, decomposed wood of the tree I found them in, with some decomposing hardwood leaves mixed in.

A communal enclosure is fine for the larvae of this species, so long as it's spacious enough that they don't get in each other's way when building pupal cells.  The cells of this genus are typically built at about a 45 degree incline, with the head end facing up.  Presumably, it's important that the cells be maintained in this orientation, in order to avoid eclosion issues.  The cells taper to a small point at the head end - no idea what purpose it serves, but the cells of some other Cetoniinae (such as Euphoria fulgida) have similar projections.  Ordinarily though, these structures will only be visible on cells that have had all of the loose, adhering substrate brushed away from their surfaces.

There's probably no need to pack the substrate.

 
- Supplemental food of dog kibble and fruit offered at the surface.

They will probably accept apple placed on the surface, but they seem to mainly focus on eating well-decayed wood.  Dog food could possibly lead to mite problems.  If you try dog food, I suggest only offering just a few pieces at first, to see if they are even interested in it.
 
- Keep the substrate damp but not wet.

Yes - same humidity level as is used for G. caseyi should work well.
 
- I'd go through the whole substrate every 6 months to separate out any pupal cells and move the batch into a new identical enclosure if the substrate is used up.

It will depend upon the size of your enclosure and how many larvae are in it, but I think you'll find that even a small number of Osmoderma larvae will convert substrate into frass at a rather phenomenal rate!

- Keep pupal cells in a separate enclosure for adults to eclose into, then feed them bananas and fruit juice, and hope they mate and lay eggs in there.

Use caution when handling the cells - Osmoderma cells are rather thin-walled and delicate.  Also, when transferring them, try to place them at roughly the same incline at which they were originally built; it doesn't need to be absolutely exact - just approximate.
 
I say all this to see if anyone with experience raising this or a related genus might like to chime in to affirm or correct anything in my plan. I've discovered another well rotted tree on my property to investigate and I may collect another 10 larvae or so. Any thoughts or tips would be appreciated. Thanks!

Wishing you success in your efforts!  I think you'll find that this species isn't difficult.  Osmoderma tends to be rather productive in captivity - almost as much so as Gymnetis caseyi.  One major difference is that a small percentage of Osmoderma larvae tend to diapause for a while at the end of stage L2.  They'll make a small chamber in which to do this, usually right at the bottom of the enclosure, and remain inactive for months.  This seems to happen regardless of the temperature at which they are kept.

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I also discovered some of these bad boys. Information has been absolutely sparse. I heard they spend 3 years as larva and only 1 month as beetles.

 

Something else I heard  - dont ever handle the papal cells if you can help it. These beetles will not develop or emerge properly of their pupae cell is broken. 

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