Can anyone ID this bug eating my plants roots?

Or what in the name of all that is agent orange are these things?

See here for some pics of a nasty looking critter. It is sat in a 55mm lens cap if you need some scale.

I was digging up some plants that were either on their last legs or had actually shuffled off from this green an pleasant world, and replanting some others ready for summer. All around the dead plants, burried to a depth of about 10 cm (4-5 inches) where these little critters,which I suspect had munched away on the roots and killed the plants.

They are about 3 cm long and appear to be hibernating (it is the tail end of winter here in Argentina). The star of our show started moving when I brought it inside in the warm, and certainly tried to chew down on the chop stick I was prodding it around with for its photo shoot. I thought it was a catapiller but it only has six legs only up at the front and a fine set of jaws.

Anyone any ideas?

Looks like a beetle grub
Where these agaves, by any chance?

Damn this place is fast
Those are the little buggers, white grubs of the may or june variety I think.
The plants were not Agarve, just some leafy bushy plants that were planted last year. Looking at the text these things may explain why my lawn is is such bad condition. It was laid down last year (new house) so I geuss the parent beetles may have burrowed into the new earth.

Anwyay, thanks for that

The reason i asked about the agave is I once had a pretty good sized one that died a rapid death. When I dug it up, it was a veritable zoo of different types of grubs - I should have taken a photo.