Insect larva to provide food on tall upright rock (11)
I believe the answer is:
caterpillar
'insect larva' is the definition.
'provide food on tall upright rock' is the wordplay.
'provide food' becomes 'cater' (I've seen this before).
'on' means one lot of letters go next to another.
'tall upright rock' becomes 'pillar'.
'cater'+'pillar'='CATERPILLAR'
'to' is the link.
(Other definitions for caterpillar that I've seen before include "Tiny creature" , "Butterfly/moth larva" , "Heavy tracked earth-moving vehicle" , "He made do with a mushroom" , "Lepidopteran larva" .)