deceit vs deception

Solution 1:

"Deception" is more closely associated with the accomplishment of purposeful misguidance or misdirection (which is often physical, as with your suggestions of mimicry and camouflage). "Deceit" is more closely related to the intention to mislead, and carries a (negative) connotation of willful malfeasance.

I think this is something of a case of "false friends," in which these similar terms are really only distantly derived from the same source, and probably should be viewed as being essentially separate, albeit related, concepts. The first ("deception") does not even necessarily carry any connotation of evil, whereas the second ("deceit") generally and usually does.

Solution 2:

To me, the answer happens to be very simple.

Just imagine the difference between "false" and "fraudulent". Just as a falsehood with criminal intent is "fraud", so is the "deception"; a "deception" with criminal intent is a "deceit".

This way, you will find "false" a bigger circle, while "fraud" finding a smaller place within that circle and so will you find "deception" taking in "deceit" and covering an area far beyond.