At what the group described as a demonstration, leafcutter ants - a species indigenous to the world's biggest forest - were seen carrying leaves bearing slogans cut out by WWF (World Wide Fund for Nature) activists such as "Save the Amazon" and "Help, Merkel".
The action organised by the zoo in Cologne aims at calling on the German leader to push for the protection of the Amazon when she meets Brazil's President Dilma Rousseff on Thursday.
"The German government should use this meeting to redouble collective efforts at protecting the Amazon tropical forest," said Christoph Heinrich, a board member of WWF Germany.
The Amazon, the largest forest in the world, has been slowly eaten away by deforestation as well as illegal mining.
Ants carrying a leaf reading "Stand up!". Photo: DPA.