Water buggy?

Question

I don't get it. The measure of a bug that is assur is "nireh l'ainayim". It took a bug light to discover that there were bugs in the water. Until then no one in a population of 8,000,000 noticed them. That called "Nireh Laynayim"! Also, this means that the size of a bug is so small that we would all ingest it without knowing that we were ingesting something assur for many years until the invention of the bug light. Does it make sense to say that the shiur is set so small so as to trick us into doing something assur? And it's called "nireh l'ainayim"?