It takes place in 1983, so maybe they weren’t a thing yet?
If you look more into it, you’ll discover these are abandoned ant colonies. No ants were harmed.
Response to This 8-Year-Old Sent Her Mom A Very Cute Email Explaining Why She Needs To See The "Hunger Games":
I can understand why a mother wouldn’t want her child to watch the movie. It deals with very dark themes, and while it may go over the child’s head, it still is something that we shouldn’t let our children watch if we feel they are too young to understand it.