I know when I buy crickets, I get little bugs in them that I was told were the larvae of carpet bettles. From what I understand, these are completely harmless and merely a sign that things are not completely clean in the cricket colony. Without seeing an actual picture of what you have, I can only guess that you are seeing the same thing. I used to have a high mortality rate with crickets as well, but since I simplified the enclosure, I have had much better success. I don't use any papertowel or ground cover with mine, especially anything overly moist. I feed a combination of predone gutload cricket food that I add crushed catfood and fish food too; cricket jelly for water; and baby carrots and some leafy greens for extra gutloading.