Grubby, immature youngster (5)
I believe the answer is:
larva
This clue might be a double definition.
'grubby' is the first definition.
The definition and answer can be both animals as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'immature youngster' is the second definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
Can you help me to learn more?
(Other definitions for larva that I've seen before include "Insect's feeding stage" , "Grub of e.g. beetle" , "Grub, caterpillar stage" , "Immature form of (insect) development" , "Insect's immature form" .)