A 55-year-old man from Farmington was seriously injured in a motorcycle crash this afternoon on Tricky Pond Road in Naples.

Merle P. Sweetser apparently lost control of his 2005 Harley Davidson motorcycle while negotiating a curve around 3 p.m. The motorcycle skidded and struck a large rock.

Sweetser, who was not wearing a helmet, was transported to the Maine Medical Center by Naples Fire/Rescue with a head injury officials described as life-threatening.

The Cumberland County Sheriff’s Office believes speed was a factor in the crash.

A nursing administrator from Maine Medical Center said this evening that Sweetser is in critical condition.