The dead butterflies, wrapped in paper and stuffed into a cardboard box, belonged to species listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora, meaning that special licences are needed for their trade.
"After checking with the services of the Solomon Islands... it was determined that the person who received the shipment had attempted to illegally sell the butterflies with forged documents," the office said in a statement.
The office, which issues licences for import and export of endangered species, said the estimated value of the rare insects was 10,000 euros. It is believed they were destined for a collector in Serbia.