Mecodema antarcticum

Mecodema antarcticum is a carnivorous carabid beetle that burrows in sand above the high tide mark on New Zealand sandy beaches. First described by Francis de Laporte de Castelnau in 1867 as Brullea antarctica, it has since been reassigned to Mecodema.^[3]

Mecodema antarcticum
Specimen from Castlecliff Beach, Whanganui, New Zealand
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Suborder:	Adephaga
Family:	Carabidae
Genus:	Mecodema
Species:	M. antarcticum
Binomial name
Mecodema antarcticum (Laporte, 1867)
Synonyms[1]
Brullea antarctica Laporte, 1867 Mecodema antarctica (Laporte, 1867)[2]

Description

Mecodema antarcticum is large (up to 25 mm), glabrous reddish brown to black with a distinct "waist" or narrowing between thorax and abdomen (peduncle), like all Mecodema.^[4] Indeed, recent DNA analysis places it within that genus, a sister group to Mecodema curvidens; its distinctive differences in body shape may be adaptations to burrowing in sand.^[5]

This species legs are well-adapted for digging in sand with greatly expanded coxa, femur and tibia: all tibia are greatly expanded at their distal ends, and the middle and hind pairs are also strongly curved.^[6] Other features consistent with dwelling in and on sand are the short antennae, large curved mandibles, and a rather boxy shape in contrast to the longer and more elegant forest Mecodema species. The abdomen of M. antarcticum is covered in long setae to further protect it from abrasion. Its larval form was unknown for some time, and was first described in 1978.^[7][8]

Ecology

Mecodema antarcticum is found in the supralittoral or splash zone of sandy beaches around the New Zealand coast, underneath logs or stones, hiding in the sand during the day and emerging at night to feed.^[9][10] It was described by George Hudson as "usually rare",^[9] but is a secretive burrowing beetle, and occasionally is discovered in reasonable numbers.^[11] It was rediscovered by schoolchildren on the Whanganui coast in 2006 after not being recorded for many years.^[12]

Mecodema antarcticum has been recorded being heavily preyed on by katipō spiders,^[11] and it may be threatened by the introduced South African spider Steatoda capensis, either as a predator or competitor.^[13]