Short-lived insect (6)
I believe the answer is:
mayfly
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">short-lived insect</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for mayfly that I've seen before include "Ephemeral insect" , "Short-lived insect with delicate wings" , "Short-lived spring insect" .)