Those look like baby slug embryos...some kind of larvae.

The ants are filling their bellies with the juices of the larvae and taking it back to the colony for ditribution to the queen.

Those slugs are prolly feeding on the stem itself sucking nutrients from the plant as it pushes them up the tubes of the stem.

I would get rid of them.

I slept in a Holiday Inn last night so I am pretty sure I am pretty correct.