The ants were Acromyrmex octospinosus and they were housed in an existing display which also had a large clear tube running around the room.
The lower two viewing windows each housed a colony of Acromyrmex ants with access to the top foraging area where two islands are separated by water and where food could be placed.
This was housing for a long displayed Atta cephalotes colony which declined over a period of time. Although not our first choice for public displays, Acromyrmex can grow to huge numbers and some displays we have seen of this genus have easily been as impressive as Atta. One of the benefits of Acromyrmex as a display subject is that they are more tolerant of dry conditions.
A classic Spanish zoo focusing on large marine animals but hosting a fantastic tropical house where we were asked to visit and bring colonies of Acromyrmex to set up in a display.