The spiky yellow woodlouse is Critically Endangered and found on St Helena in the South Atlantic Ocean.
It is one of a number of endemic and rare species on the remote island.
The spiky yellow woodlouse is the only the second woodlouse species known to glow under ultraviolet (UV) light, a feature that is more commonly seen in scorpions.
As well as being an extraordinary find, the fluorescence has helped researchers to find the species during surveys.
The woodlouse is normally difficult to spot against the fern fronds, but the UV torch has enabled the surveyors to find it more easily and even find it in new locations.
“As many as 57 individuals have been counted in a five minute search,” said Amy-Jayne Dutton from St Helena National Trust. “An astonishing number for a species whose population was originally thought to number 50 in its entirety.”
With its striking prickly appearance and its tendency to live on trees and ferns, the spiky yellow woodlouse was already known to be quite unusual and this latest discovery adds to this species’ list of interesting characteristics.