Lucilia hanging on the wall (12)
I believe the answer is:
greenbottles
'lucilia hanging on the wall' is the definition.
I can't tell whether this defines the answer.
'on the wall' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for greenbottles that I've seen is " Flies".)