The "abundant gathering" of purple copper butterfly caterpillars was found at a location where there had been no recorded sightings since 2009.

They were discovered by volunteers and staff from Central Tablelands Local Land Services, according to senior land services officer Allan Wray.

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He said the location was one of a number of trial treatment sites where strategic ecological burns were conducted three years ago on small five-metre by five-metre patches of blackthorn, which is the only known feed source for larvae of the endangered purple copper butterfly.

"The aim of the cool burn technique is to promote the regrowth of native blackthorn and to reduce competition from grasses and weeds," he said.

"The low temperature burns singe the mature bush without destroying the plant, prompting regeneration and new soft leaf growth which is believed to be particularly appealing to the young caterpillars."

Mr Wray said many of the existing blackthorn shrubs were old and covered in lichen, which he suspects made them less appealing to the butterflies.

"The strategic burns promoted fresh regrowth and improved the general health of the shrubs, which in turn should enrich vital habitat for the purple copper butterfly," he said.

He said the sighting of so many caterpillars was a great result for everyone who had worked "tirelessly on this experimental project over the years".

"It's a positive start to the life cycle and we're all looking forward to September when the butterflies typically emerge and take flight," he said.

One of Australia's rarest butterfly species, the purple copper butterfly is only found in a few small pockets of native vegetation at elevations above 900 metres between Bathurst, Oberon and Lithgow.

For more information about the purple copper butterfly and advice on how to enhance native vegetation and remnant habitat, contact Allan Wray at Central Tablelands Local Land Services on 6333 2318.