Threat Thursday stays in the Swartland: as aristocratic as Wallengren's Silver-spotted Copper might sound, it is "Critically Endangered"
Last week, Threat Thursday focused on Schlosz's Opal, which occurs on just one hill near the village of Koringberg in the Swartland region of the Western Cape. The butterfly for this weeks's Threat Thursday occurs on just two hills, also in the Swartland. Today's species is the "Critically Endangered" Wallengren's Silver-spotted Copper Trimenia wallengrenii wallengrenii. Neither the silver spots or the long aristocratic-sounding name are helping this butterfly now. It is going to need a serious conservation intervention to save it from extinction.
Wallengren's Silver-spotted Copper has two remaining localities, neither of which can be described as strongholds. One is on the Kapokberg and the other on the Contreberg, south and south-east of Darling, respectively. Each locality is about 700 m2 in extent. The two sites are 7.5 km apart. The Kapokberg locality has had very few specimens in the last 10 years (probably no more than 50 adults per flying season). The Contreberg site has shown considerable fluctuations in population numbers; there were about 100 adults here in November 2003. No adults have been observed at another recent locality north of Mamre for nearly 15 years, so we can assume that they have become extinct there.
The habitat in which this butterfly currently occurs is known as Swartland Granite Renosterveld. In the past, the butterfly was also found in the ecotone between renosterveld and Sand Plain Fynbos. No life cycle information has so far been published. The larvae are probably aphytophagous, with an obligate ant association. Adult butterflies were noted to fly low and fast, in open areas. Autecological studies are urgently needed to determine the critical resources needed by the butterfly.
This subspecies is threatened by habitat destruction and degradation from agricultural activities (wheat farming) and invasive alien vegetation. Fires, when the adult butterflies are on the wing, can also be devastating. Originally it occurred near Stellenbosch and a number of other places closer to Cape Town, but extensive agricultural activities have led to the extinction of all these colonies. The two places where it has survived are a few places situated on higher, rough or rocky ground, which have escaped the plough. In some cases cultivated areas extend right up to the borders of the existing colonies. Severe fragmentation of its habitats near Darling has already taken place and the lack of dispersal routes and connecting corridors have become major concerns for the long-term survival of the butterfly. These last two subpopulations are both on privately owned farms. Urgent monitoring of this taxon and research into its ecological requirements and life history, followed by design and implementation of a habitat management plan are essential if extinction is to be avoided. The LepSoc "custodian" of this species is Jonathan Ball. These three photos are by Steve Woodhall; the top one shows a male, and the photo below shows the underside of a male. The photo at the bottom is a female.
You can learn all about the butterflies of South Africa, Lesotho and Swaziland by purchasing a copy of the "butterfly atlas." The window of opportunity to buy this book closes on 31 March. We will print as many copies as are ordered. To buy your copy, go to adu.org.za/sabca_book.