"Army Ants" Invade Clinic

During an examination yesterday morning, Sebastian pointed out that ants were flooding into the room under the door. An area for a foot or so in front of the door was swarming with tiny black ants about 1.5 cm long. 

Behind the door on the wall was an "army" of ants, moving in formation,down to the floor underneath the door. The rearmost portion of the army went up and over the wall. 

In the pharmacy on the other side of the wall, the ants marched up a corner in the room.

The start of the invasion was one of the ventilation holes in an opposite wall. Why the ants chose the direction they took is not evident.

The forward most ants were brushed away and the leaders of this formation acknowledged defeat and the army quickly dispersed, presumably outside the clinic. They seemed to appear and then disappear within a half an hour or so!