I live in a basement in the California Bay Area. A week ago I

holy FUCK

That shit nasty

there is a dead body behind that wall.

>>274398
This. Seriously.
Sounds like the larvae may be Rostrozetes foveolatus which are mites that feed on dead skin/tissues after most of the decomposition has occurred. Either that or Silphidae, aka Carrion Beetles.
With the stuff coming through the concrete, it sounds like the second. Silphidae are known to excavate and build tunnels, and it sounds like what you are getting is the waste soil, feces, and larvae that they clean out of the 'nest'.
You have a difficult choice to make here Does your landlord know about this? If not you may want to keep quiet about it. I mean obviously if there's evidence of a cadaver under/behind a concrete wall, that means somebody put it there. And how far would that person be willing to go to keep it quiet?
If they do know about it, I suggest watching your back. Possibly getting out of there and contacting the authorities.

One thing while I think about it, is there an odor to the stuff that's building up? If so what's it smell like?

>>274283
Are you dead OP? Give us updates when you get back.
>>274749
If larvae are still coming out of the wall wouldn't the body have to still be fresh? How could a body still be there with OP not noticing the smell for so long?
Maybe its a dead cat or raccoon that died recently.

>>274894
Depends on the type of insect.
Various stages of decomp will have various types. Flies, etc are usually the first, then as the body decays different species take over.
The last being Rostrozetes foveolatus and/or Silphidae.
There's been cases where these were found years after a body have been hidden.