I wish that we could see the other side.....insect larvae are difficult to ID from their tummies. It's a beetle larvae of some kind.

I checked the other photos.

Not a lot of identifying features, I will admit.

I am trying to feed it, but I haven't had a lot success in this area in the past.

It is a vegetable garden, so nothing too toxic.

Do I need to get a big syringe and inject the ground under the plants?

I had the leaves fall off some pepper plants last year. Then they died. Maybe it was due to these grubs eating their roots.

As big as they are, I don't think that I am going to find any natural predators unless I could import some sand worms from the planet Dune.

The Wiki page says that they roll onto their backs and propel themselves upside down, so that would be a photo of his belly that I took.

You live and you learn, I guess.

Slug, for ONE grub you do nothing....absolutely nothing. Feed it to the birds while it is still alive so it won't 'die in vain ', lol.

No to pesticides being injected into the soil for several reasons. For one, you don't know what it is. You can't even be certain of what it feeds on. We don't use pesticides without a much better idea of the identity of the culprit.

More than likely it;s the larva of the green fruit beetle.

If so, it doesn't damage living plants.
It is common in compost piles or highly organic garden beds.