A fleecy fugitive from a bluegum plantation in WA's south has finally met its match in the shearing shed.

Brian the ram was carrying about five years of wool when it wandered out of the harvested plantation near Boyup Brook last week.

The animal was far from sheepish about joining the flock at a neighbouring property.

"It was there in the mob when we went to weigh the new season's lambs," livestock agent Brenton Tynan said.

Boyup Brook farmer John McKenna said Brian was one of half a dozen feral rams or sheep that had made a home among the gum trees in recent years.

"They were having a great old time in there," he said.

"We can remember seeing a lamb in there amongst them a few years ago, and we think this one is the lamb who's grown into a ram.

"By the look of the wool on him and his teeth we think he's about five, five and a half years old."

A local shearing contractor was called in to relieve Brian of its fleece, which weighed in at 18 kilograms and measured 4.5 metres.

The fleece will be donated to a charity auction for the local branch of the Royal Flying Doctor Service, and is expected to fetch about $200.

Mr McKenna said it would be quite the transformation for Brian.

"I just hope he doesn't get sunburnt," he said.