Shorts: A UV fluorescent isopod

On a remote volcanic island in the middle of the South Atlantic ocean, a familiar yet alien isopod calls St Helena home. The bright yellow colour and spikes are not the only remarkable things about these woodlice, they also glow under UV light!

It’s 2017. After 6 days on the RMS St Helena from the west coast of the African continent, you finally arrive. Hoisting your backpack onto your shoulders you jump from the boat onto dry land and take in the island before you. This 47-square-mile island is 1,200 miles west of Angola and 2,500 east of Rio de Janeiro, so “remote” is quite an apt description for this island. Formed 14 million years ago from a volcanic eruption, like many isolated islands St Helena holds a whole host of endemic flora and fauna.

Psuedolaureola atlantica

If you were hoping to spot the endemic spiky yellow woodlouse (colloquially named Spiky’s, species name Psuedolaureola atlantica) you would be incredibly lucky if you managed to. These woodlice are not found on the ground like other woodlice, but up in trees and ferns. Their bright yellow colouring disguises them well among the foliage they inhabit, but only 50 are in existence and all inhabit a small patch of black cabbage tree woodland named The Dell in the island cloud forest. The fragility of this ecosystem combined with the number of individuals makes this species critically endangered.

However, 2017 is a year for good news for the spiky yellow woodlouse. During field surveys in 2017, it was found that the Spiky’s have the remarkable ability to glow under UV torchlight (wavelength 395nm). This feature is more commonly seen in scorpions but has only been seen in one other woodlouse, a terrestrial cave-dwelling Mesoniscusgraniger.

Suddenly transects that appeared to host few to no Spiky’s in previous surveys were bustling with life. Spiky’s were not found on other species of flora outside of the narrow list they were thought to inhabit, and in multiple different locations outside of the small area, they were seen to inhabit before. It has also helped provide a more accurate population number, which is now thought to be around the 1000 mark.

Although their “critically endangered” label still applies, these wonderful spiky glowing isopods are not as dangerously close to extinction as we had thought. With the conservation work the St Helena National Trust has planned, hopefully, the mysterious spiky yellow woodlouse will continue to flourish and remain part of the 400 endemic invertebrate species on the island.

Papers and further information:
UV fluorescence in a critically endangered isopos, Pseudolaureola atlantica, Dutton A & Price D, 2018
Spectroscopic parameters of the cuticle and ethanol extracts of the fluorescent cave ispod Mesoniscusgraniger, Giurginca A et al,  2015
St Helena National Trust website