A balanced diet for feeder insects, enriched with vitamins to improve the nutritional content of the bugs (gut loading) before feeding them to your reptile or amphibian.

Here's what the manufacturer says about their product:

We have spent several years working with our insect feeds BUG GRUB and GRUB GRUB to develop a single product which covers the needs of both groups (hoppers and mealworms) and to produce the best gut loading effect we can.

Now we have NUTROGRUB - based on a fine vegetable flour enhanced with our world leading supplement NUTROBAL and its superfine calcium. This has been a roaring success and has resulted in increasing calcium levels in crickets by MORE THAN TENFOLD ie x 10, and in mealworms MORE THAN SEVEN FOLD ie x 7. The tests were carried out by an independent laboratory and impressed even us!

The protein level is low enough that the mealworms don't mature too quickly, but more than adequate for support of the feeder insects.

Gut loading is useful in increasing calcium levels but for belt and braces we still always recommend dusting with Nutrobal as well.