The 220-square metre (2,400-square foot) greenhouse in Lisbon's botanical gardens currently houses around 100 butterflies from eight different species and the goal is to eventually display 20 different butterly species, the director of the gardens, Maria Amelia Loucao, said.

"There are many other greenhouses in Europe that display tropical butterflies in heated environments but this is the only one dedicated only to European species that is open to the public," she told AFP.

The aim of the project is to educate the public about the life cycle of European butterflies, which varies among different species, and their interaction with the environment.

The sprawling botanical gardens, a quiet refuge in central Lisbon founded in 1874, attracts 60,000 visitors each year, mostly in spring and summer.