From where they came?(instects & worms)?

Question

We usually see that if any flour remains long time, there is small worm and instects in it.
Initially there is nothing in flour but as time passes worms appears, from where they came?

Answer 1

moths got into your flour containers & lays eggs. they have got in from the shop or warehouses b4 u brought it.

Answer 2

Their egges were present already or were laid by insects.