Fatter Worms make better bait. Fattening your worms up makes for bigger fishing bait, or if you are selling them, less worms per pound.
A cautionary note, if too much of your worms' diet is grains, they can develop what is called acid poisioning making the worms lumpy, otherwise known as "string of pearls"
 
I've included several other recipes I've collected. To use these dry foods, be sure to keep feeding your worms a normal diet and just add a sprincle of this to the top of the bin each day.
If they eat it all, add a bit mor ethe next day, if not, skim off the excess and add new feed in a smaller amount.
 
For the purposes of these recipes eggshell, garden lime and diatomatious earth all provide similar effects of adding calcium and grit. Feel free to substiture based on what you have available.
 
Here's the recipe I use.
2cups oats (ground)
1 cup cornmeal
1/4 cup ground eggshells
 
Below, I've including all the other recipes I've found in my internet travels over the years as well.
 
Alternative Recipe #1
1 part cornmeal
1 part wheat flour
1 part oats (ground)
 
Alternative Recipe #2
5 parts chicken layer mash
2 parts wheat or rice bran
1 part agricultural lime
1 part wheat flour
1 part powdered milk
 
Alternative Recipe #3
5 cups chicken layer feed
1 cup cornmeal
1 cup powdered whole milk
2 cups wheat bran
1 cup agricultural lime.