The Bogong Moth, once observed in their thousands on the Border during their annual migration, is now on the global endangered species list.
The moth was among Australian species added to the International Union for Conservation of Nature Red List late last week.
The Australian Conservation Foundation nature campaigner Jess Abrahams said reduction in populations was also threatening the critically endangered pygmy possums.
"The reason for the moth's sudden decline is not entirely clear, but scientists believe a mix of extreme droughts, pesticides and changes in agricultural practices may be responsible," he said.
"The Bogong moth's population crash - and its cascading impact on other species - should concern every Australian."
In February, a research team including Monash University found food remains of Bogong moths on a stone tool in the Alps from 2000 years ago.
Traditional land owners describe ceremonies to feast on the Bogong moth going back thousands of years, and have held a festival at Albury's Mungabareena Reserve.
The study also found the Bogong moth, known to have been in decline, continues to be a key dietary item for the possum.
The International Union for Conservation of Nature Red List is separate to the Commonwealth's threatened species list.
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