Small insects (4)
'small insects' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ants that I've seen before include "Hard workers" , "Industrious insects" , "workers found returning" , "Small social insects" , "Inhabitants of a formicary" .)
(Other definitions for bugs that I've seen before include "Secret listening devices" , "Small crawling creatures or disease-germs" , "Errors in computer programs" , "Software problems" , "Insects or faults in a system or machine" .)