Harmful or Beneficial Grubs/Larvae?

Hi all!  I was evaluating my orchard today, when I discovered that there are hundreds of this type of grub just under the woodchip mulch under almost every tree in my orchard.  I googled what they are and it looks like they are either June bug or Japanese beetle larvae.  I read that they eat organic matter including roots.  My initial reaction was to bring the chickens over and have them feast on the little buggers, but after some closer examination it looks like they may actually be beneficial.  It looks like they are leaving a lot of grub castings behind, which I imagine is a great fertilizer.  I don't know how much damage they will cause when they become adults.  Anyone have any experience with them?  Beneficial or harmful?  Kill em or leave em?  Thanks!

Oh man. Japanese beetle larvae. Those grubs eat roots, generally grass roots is what they're known to eat. Sometimes lawns with high populations of them will have brown patches of grass in the summer when things get dry from grub activity eating the roots and the grasses can't get water from deeper in the soil. The adults are the enemy. They'll ravage annual garden crops and also perennials like fruit trees doing considerable damage and high populations can be devastating. I highly recommend turning those chickens loose to eat those grubs!

Ok, thanks James!  Unleash the chickens!!

Man those chickens are gonna have a good day. They'll make a mess scattering the mulch around scratching for grubs, but I'll take tidying up with a rake any day over japanese beetle infestation destroying a crop of something I was planning to eat.