The rare sight was captured on an infrared camera as the beaver - native to North America - sank his teeth into a large trunk.
Filmed by a retired scientist, it is thought to be the only sighting of a wild beaver on these shores since they were hunted to extinction in the 16th century.
Conservationists have introduced several small groups back into captivity in the UK - but this is said to be the first example of one found living in the wild.
Environmental scientist Tom Buckley set up his specialist equipment after a string of sightings around Ottery St Mary, near Exeter, Devon, in recent months.
He used a 'trail-camera', which automatically takes photos when it picks up signs of movement, and positioned it at several points around a small island owned by local farmer David Lawrence.