Alien Larva

Larvae are not produced by the pillar itself and nothing summons them. They exist because an Alien Queen died, which leaves two or three of them on the ground inside the Vortex Pillar's area during the Lunar Events. That makes them the tail end of the cycle rather than the start of it.

Left alone, each one crawls about until it becomes an Alien Hornet, and the hornets grow back into queens. Kill a queen, walk away, and shortly afterward you are fighting that same queen again for nothing. A later patch capped how many the family can hold, so a queen will not release larvae if enough hornets are already alive, but the loop still drags the pillar fight out if you ignore it.

This is the harmless stage and the cheap one to remove. They shuffle slowly along the ground, they cannot fly, and anything with area damage sweeps them up along with the rest of the wave. Do it right after every queen kill rather than sorting it out later.