I have read not to use spinach, I think it is thought to have an inhibitor of calcium or to that effect. I was in the grocery store so I started looking at vegetables. Spinach per serving seemed to be higher in calcium than the others, but whatever spinach contains or may contain makes me choose not use it. 1 Idaho potato that equals 1 serving has 2% calcium, but I found these Melissa's Dutch Yellow Baby Potatoes(about 2" X 1") and it takes 4 to equal 1 serving and they are 8% calcium per serving. I feed these to my crickets along with carrots; but when I am gutloading right before feeding I use carrots, collard greens, romaine and I am looking to begin using oranges too.I feed him crickets twice a day. The crickets are dusted with calcium and eat carrots and spinach.