Insect - call it the beginning of the end (7)
I believe the answer is:
termite
'insect' is the definition.
(I know that termite is a type of insect)
'call it the beginning of the end' is the wordplay.
'call' becomes 'term' (to term something is to call it something).
'the beginning of' suggests taking the first letters.
The initial letter of 'end' is 'e'.
'term'+'it'+'e'='TERMITE'
(Other definitions for termite that I've seen before include "White ant" , "Six-footer" , "Mound builder" , "Social type" , "Ant-like insect that feeds on wood" .)