Towards Hibernation

My two captive larvae coloured up ridiculously early this year. This one was photographed on 14th Oct and went into hibernation on or around the 20th - 

That's early, very early...  And they are on a bush which stays suitably green well into November.

I checked six in the wild last Sunday (the 19th), and found that they were colouring up fast.  

Looks like they're going into hibernation early, which is odd as they changed into the 3rd instar rather late.  

All this begs the question of what do they know which we don't?????