Insect — call entomologist initially to capture it (7)
I believe the answer is:
termite
'insect' is the definition.
(I know that termite is a type of insect)
'call entomologist initially to capture it' is the wordplay.
'call' becomes 'term' (term can mean to call something by a name).
'initially' suggests taking the first letters.
'to capture' is an insertion indicator.
The initial letter of 'entomologist' is 'e'.
'term'+'e'='terme'
'terme' enclosing 'it' is 'TERMITE'.
(Other definitions for termite that I've seen before include "Woodworm of warmer regions" , "Ant-like insect that feeds on wood" , "Whitish antlike insect" , "White ant" , "Mound-dweller" .)