Hill builders (4)
I believe the answer is:
ants
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hill builders</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ants that I've seen before include "Soldiers" , "Six-foot insects" , "Industrious insects" , "Tiny insects that live in colonies" , "workers found returning" .)