As the mealworms grow, they shed their skins. All these skins will accumulate on the top of the substrate. You can blow them off outside. When it is very windy, I take the drawers outside and the wind takes care of all those skins. The worms are white when they first shed the skin, and that is when the finches like them best, as then they are nice and soft.
Eventually, the worms turn into pupae, sort of cream colored things that look dead, but if you touch them, they will wiggle. From that stage, they turn into beetles. The beetles lay eggs, the eggs turn into mealworms, and the cycle is on again.
Some people lay a few sheets of newspaper on top of the substrate, and the worms collect there. I just scoop out a big bunch of substrate, and sieve it thru a fine strainer--just keep shaking it till most of the substrate falls thru. The tiniest of worms will also fall thru, so don't throw this out, just add it back into your drawer.
The best way to do the beetles is to put them in a clean drawer with fresh substrate, so they can lay their eggs in this substrate. Then, when the beetles die off, leave that drawer to rest for a while. One day, you will notice the whole substrate seems to be moving--you have worms!!
I give the drawers that have beetles or mealworms some raw potato--just slice a small potato in half. They will eat this up.
Also, you will notice that as the substrate gets used up, you will see a slightly darker, very fine material--that is mealworm poop! Wonder if that would make a good fertilizer, like earthworm poop?
