Hello spec:
I haven't found anything that stated oakmeal was bad for crickets but I did find the site where a receipe to make your own cricket food was. For convience sake, I pasted the receipe below, and the link to the site I got it from below that...there are also caresheets there for other feeder insects, including roaches and locusts:
"Cricket food must be of good quality - there are some good ones available, but you can make your own. This is the recipe:-
Rolled Oatmeal (4 cups)/ Dried Milk Powder (2 cups) / Dry Cat Food (low-protein), crushed (2 cups), Rep-Cal Calcium with D3 (2 teaspoon). Mix it all together and feed it to your crickets, it's a lot cheaper than buying it- don't forget fresh vegetables and half an orange!"
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