Destructive migratory insect (6)
I believe the answer is:
locust
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">destructive migratory insect</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for locust that I've seen before include "Large insect" , "Destructive winged insect" , "Grasshopper of warm regions" , "Migratory crop stripper" , "Sort of migratory grasshopper" .)