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Photo#415074
The big one is Trimitomerus riversii, but is the small one the same sp.? - Trimitomerus riversii

The big one is Trimitomerus riversii, but is the small one the same sp.? - Trimitomerus riversii
Picture Rocks, NW of Tucson, Pima County, Arizona, USA
June 19, 2010
Size: 6.5 and 17mm
I've collected 10 mm ones before. this 17 mm one is a giant and came to the light at the same time as the tiny one. I do not know what the females look like. I was told the ones that come to the lights are males

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The big one is Trimitomerus riversii, but is the small one the same sp.? - Trimitomerus riversii The big one is Trimitomerus riversii, but is the small one the same sp.? - Trimitomerus riversii

from D.A. Pollock:
"the fact that there is so much variation (indeed, even within sexes) in size tells me that the larva is likely living in rotting wood of some kind. I've seen size variation like this (albeit not quite so drastic) in Pytho. I think that the larva hits some kind of critical size and proceeds to pupation. Some larvae get well fed, while others don't. I'd really like to get down there again (presumably southern Arizona) and try to find larvae, or even collect live adults for rearing...
"Nice critter though. Still technically incertae sedis I think, but tending towards Pythidae. I think that Lawrence might have a candidate larva from tamarisk...."

 
He's of course welcome to try
we let a lot of palo verde wood decompose where it falls. So if that's where the beetles come from...We seem to get quite a few every year, but I can't get him females so far.
I'm surprised that they should turn out so differently if they develop in wood. That seems such a non-limiting resource. I was expecting brood-parasite or something like that.

 
quite the opposite
from experience, it is the wood borers, esp. those developing in dry wood/timber, who show the most amazing size variation

the size range is stunning but not impossible...
the genus is apparently monotypic; i alerted Dr Pollock who shall be able to shed some light

Moved from ID Request.

 
Yes, no other sp
in the genus...

 
both are males, btw

 
So I have yet to find a female

 
T.r.
not commonly seen, but when they come to lights, they can come in numbers. In June or July, 2007 (cant remember month), Bill Warner and I collected several off the Salt River outside Phoenix, in a mesquite bosque.

 
I get males every year
in early summer at our house

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