Magnetic dirt particles?

[Ratmosphere]

Collected massive amounts of substrate in the woods. Few days in the warmth there were these little magnetic looking dirt particles on the walls of my closet. 
 

Tried to get the best pics I could of them. Never seen this before, what could they be?

 

[Goliathus]

The size and shape of the objects is so regular, that they certainly appear to be either organisms themselves, or structures created by organisms (possibly small dipteran larvae of some kind).  If they're moving out of the substrate on their own (probably in response to the temperature change), they must be alive.  Can you get any sharper a photo of them?  Are these attached to glass?  Did you sterilize the substrate?

 

[Ratmosphere]

No, I did not sterilize. They are attached to the plastic part of the lid. 

 

[Goliathus]

My guess is that they might be desiccated fly larvae of some kind, or possibly, dried up nematodes.  Really though - that's only a guess.  I do seem to recall having seen something similar in my own enclosures, at times.