Those teeny, tiny, barely there ones, of which I would doubt there is anything capable of weighing them them!
Somehow they find their way in and, if didn't fall victim to my vacuum, would hang in a corner (high or low) till they finally deceased themselves.
Tried to grab one just now but somehow it escaped, and I've never seen one move and christ could it shift!
Despite the fact they are so small, they must have eyes, and a mouth, and stomach etc, but the real mystery is from where did they come, and how do they survive on nothing, and how do they procreate?