These poor adult ants are struggling to move a pupa that is considerably larger than themselves. They are moving a future "reproductive" ant (either a queen or drone) that will help start a new colony. Note the large larva in the top of the photo.
They are called "acrobat" ants because they often raise their heart-shaped abdomen when disturbed. If these ants had not been so busy trying to move the pupa, they probably would have had their abdomens raised!