The knobbled weevil were apparently common over the Canterbury Plains in the 1870s. Possible causes for its disappearance were the removal by farmers of speargrass (Aciphylla), its host plant, and the arrival of predatory European rats. It was last seen in 1922, and was considered extinct until it was rediscovered in late 2004 by research students of the University of Canterbury at Burkes Pass near Lake Tekapo, South Canterbury, New Zealand. It is now listed as nationally endangered by the New Zealand Department of Conservation, and as critically endangered in the IUCN Red List. A detailed ecological study conducted by researchers at Lincoln University in 2009-2011 estimated the population size at Burkes Pass to be only 138 individuals in 2009, decreasing each year to 76 in 2011.