The spiky yellow woodlouse, Pseudolaureola atlantica, is one of the rarest invertebrates in the world. It has long been considered a flagship species for St Helena’s highly threatened invertebrate fauna, and is well known amongst islanders for its bright colours and unusual appearance. However, very few people have seen one in recent years. In fact, numbers have declined alarmingly since the 1990s.
Woodlice are not insects but ‘isopods’, more closely-related to shrimps and other crustaceans. Almost all species feed on dead organic matter, but the spiky yellow woodlouse is a remarkable exception: It virtually never visits the ground, but lives its entire life clambering amongst fern fronds, where it probably feeds on spores. No one yet knows what the vivid colours and elaborate ornamentation are for, but they could confer a degree of camouflage or provide a bold statement to ward off predators.
A habitat under threat
The species appears to be restricted to the understorey of black cabbage tree woodland, a habitat unique to St Helena. Black cabbage is one of the island’s endemic ‘tree daisies’. Its spreading canopy drips with ferns and mosses, and provides a very dark and humid environment ideally suited for ferns to flourish. The cloud forest environment is also ideal for an isopod very vulnerable to drying-out. The remaining individuals are restricted to only the dampest of micro-habitats, where the relative humidity remains almost constantly above 90%.
Unfortunately, extensive stands of black cabbage tree have almost disappeared. Only a few tiny fragments remain near High Peak, providing home for approximately 100 woodlice. The last vestiges of forest are vulnerable to high winds and deteriorating at an alarming rate.
The rescue plan
In order to save the spiky yellow woodlouse and the other special species which are associated with black cabbage tree woodland, action is urgently needed. In response to the critical situation, the St Helena National Trust and a number of project partners have combined to initiate a rescue plan. This commenced in 2012, when the Flagship Species Fund (Flora & Fauna International/DEFRA) provided a small grant to obtain basic data on the species’ biology. Surveys were conducted in an attempt to find more colonies, and hours of painstaking observations made to study the animals’ daily behaviour. The scientific study provided the basis for a larger scale conservation project, which is currently being implemented thanks to a grant from the Darwin Plus Initiative. Efforts are under way to restore a larger area of suitable habitat and to link the main site with other isolated black cabbage trees scattered around the High Peak area. A captive breeding programme is also in development, to be housed at St Helena Government’s conservation nursery facility (‘Scotland’, in the island’s St Paul’s district). It is too early to say whether this will be a success, but the population is now so small that we cannot afford to leave its survival to chance. Thanks to the extensive research efforts, we are hopeful that we can provide for the exacting needs of this thoroughly unusual and intriguing animal.
The conservation programme has been supported by the Royal Society for the Protection of Birds, the Zoological Society of London, Buglife UK and the St Helena Nature Conservation Group. We also owe thanks to St Helena Government’s Endemic Plant Nursery who have supplied plants for habitat restoration.