Holcaspis brevicula, the Eyrewell ground beetle, is a species of carabid beetle native to New Zealand, one of a number of small black flightless beetles in the genus Holcaspis that inhabit the dry eastern lowlands of the South Island. H. brevicula is very rare—only ten specimens have ever been collected—and critically endangered: the species was found only in Eyrewell Forest, a single plantation of exotic pine trees currently being converted into dairy farms.
Description
H. brevicula was named and described in 1984 by Michael Butcher in a revision of the genus Holcaspis. At that point it was known from only two male specimens, both collected in Eyrewell Forest on the Canterbury Plains in 1961. H. brevicula can be distinguished from its slightly larger close relative H. algida by the patterns of punctures and setae on its pronotum and elytra, and by the male's shorter aedeagus. It is a small (10–11 mm long) shiny black ground beetle, and is flightless, predatory, and probably nocturnal. As adults have been collected during winter months, H. brevicula probably lives for over two years – relatively long for a beetle.
Distribution
The Eyrewell Forest area has dry, stony, free-draining soils, and its original vegetation area was probably kānuka (Kunzea serotina) shrubland and forest up to 10 m high, with some tōtara (Podocarpus totara). This habitat was widely burnt off by Polynesian and European settlers, and now exists on the Canterbury Plains only as small fragments, less than 20 ha. There are several such fragments in the Eyrewell area, the largest being the 16 ha Spencer-Bower Reserve. All are on private land, some protected by a QEII covenant, except for the Eyrewell Scientific Reserve (2.4 ha), which is administered by the Department of Conservation.
The poor soil at Eyrewell was considered unsuitable for agriculture and used mainly for sheep farming. Between 1928 and 1932, the tall mānuka (Leptospermum scoparium) forest at Eyrewell was cleared and the 6764 ha Eyrewell Forest plantation of introduced Monterey pine (Pinus radiata) was established. Most of the area has been in plantation forestry ever since, with blocks of trees being felled in rotation approximately every 27 years. Some of the older blocks had an understory of kānuka up to 4 m high and most included native shrubs, herbs, and mosses, despite regular tree felling and replanting.
Holcaspis brevicula was present in kānuka forest at the time it was knocked down and interplanted with pine trees, and has persisted in the regularly-felled plantation forest. At the same time it has disappeared from the remaining fragments of nearby kānuka forest, which appear to be too small, increasingly degraded, and browsed by sheep to support populations of the beetle. Intensive searching and pitfall trapping in remnant kānuka forest, pine plantation, and adjacent pasture, comprising 57,494 trap days over 2000–2005, captured five more specimens of H. brevicula. All were found in the pine forest. Three more specimens, collected between 1956 and 1967, were located in the Forest Research Insect Collection. All the ten known specimens of this beetle came from the Eyrewell Forest, which thus contains the only known population of this species.
Conservation
Because of its rarity and single locality, H. brevicula is classified as "nationally critical and under acute threat of extinction". It was chosen as one of the 150 priority species in the Department of Conservation's 2017 Threatened Species Strategy. The beetle has no legal protection under the Wildlife Act, and in New Zealand plantation forests on private land can be felled, even if they are the only habitat of a threatened species.