Soldiers are regularly taking DNA test (4)
I believe the answer is:
ants
'soldiers' is the definition.
(soldier is a type of ant)
'are regularly taking dna test' is the wordplay.
'are' becomes 'a' (short for 'are', historical unit of measurement).
'regularly taking' indicates alternate letters (letters removed at regular intervals).
'dna'+'test'='dnatest'
The alternate letters of 'dnatest' are 'nts'.
'a'+'nts'='ANTS'
(Other definitions for ants that I've seen before include "workers found returning" , "Hard workers" , "Tiny insects that live in colonies" , "Inhabitants of a formicary" , "Termites" .)