Did you figure out what the black ovals from the photograph in the recent Lasius post were?
Although aphids give birth to live offspring during parts of their life cycle, they also lay eggs during certain stages. Those stacks of black ovals are root aphid eggs tended by Lasius ants.
The following excerpt from Applied Entomology: An Introductory Text-book of Insects in Their Relations by Henry Torsey Fernald (1921) talks about the life cycle on one root aphid, the corn root aphid:
Note: This book is now out of copyright. The excerpt is from Google Books.
Have you ever seen ants tending the eggs of another species?