hhhmmm....most grubs eat grass roots or wood pulp....

? look up soldier fly larvae and see if this is what you got?...segmented and sort of flat....there were literally millions of them in my mouse bedding pile years ago...when i had one....they look like blue wasps as adults....
I actually cannot remember anything under my rabbit pens...and I would make manure tea in 4 buckets everyday for my tomatoe plants ..there for awhile....(rabbit manure will NOT burn plants...it is great fertilizer...you can use it straight up or make a tea from it and pour it right on plants and all.....)...

....
-----
........JY