It might not be pretty, but an obscure native bug found alive and well after being thought extinct is just as important as the kakapo, says an entomologist.

Canterbury Museum entomologist Peter Johns has found so many Canterbury knobbed weevils, Hadramphus tuberculatus, which previously had not been seen since 1922, that it has escaped a category one "critically endangered" Department of Conservation rating.

Mr Johns' search was prompted by University of Canterbury masters student Laura Young, who found a weevil in a reserve near Lake Tekapo while studying native speargrass - its favoured food. Mr Johns trapped three weevils in one evening.

"The results were so terrific, I recommended a reduction in the weevil's classification," he said. "It might not look very nice, but from a biodiversity point of view, it's just as important as the kakapo."

While the weevil was confined to areas of speargrass a new estimate of numbers meant it would get an endangered rating only, said DoC scientific officer Rod Hitchmough.

The weevil is between one and two thumbnails long and, unlike introduced weevils, was not a pest, Mr Johns said.