Mecodema howittii

Mecodema howittii is a species of ground beetle in the genus Mecodema that is endemic to New Zealand. It is only known from Banks Peninsula in the Canterbury region. It is the largest of the endemic carabidae found on the peninsula. Because of a significant reduction in its distribution, it is considered to be a declining species. M. howittii is most commonly found underneath logs during the spring and summer, primarily in forest and grassland habitats including pasture. The species is nocturnal and known to prey on other invertebrates.

This species was originally described in 1867 by Francis de Castelnau from a specimen collected near Christchurch. The specific name refers to the collector, Australian entomologist Godfrey Howitt, and de Castelnau noted it was the largest Mecodema species he had encountered.^[1] Although the specific name chosen by de Castelnau was Howitii, later entomologists have often referred to it as M. howitti.^[2][3][4] The type specimen is stored in the Genoa Museum.^[2] The species was described again just a year later by Jules Putzeys as Mecodema rectolineatum, and then again as Mecodema walkeri in 1904 by Thomas Broun.^[5][6] These species names were later synonymised in 1874 and 1949 respectively.^[7][2] The species was most recently given an updated description by Britton in 1949, when was assigned to the costellum species group.^[2]

M. howittii is the largest of the 10 endemic ground beetle species that can be found in Banks Peninsula, measuring 26–31 mm (1.02–1.22 in) in length.^[3] Similar in appearance to other Mecodema, this species can be distinguished by the structure of the elytra and the presence or absence of setiferous punctures (depressions in the body with a hair in them).^[2]

The overall body colour is black. The vertex of the head has a smooth texture with a depression and faint (or in some cases absent) punctures. The basal section of the labium has three punctures on either side. The margins of the pronotum have ten to twelve punctures on the lateral margin. The third and fifth elytral intervals are flattened, the second, fourth, sixth and eighth intervals are smooth with two rows of punctures each, and the first, third and seventh intervals are smooth with fine wrinkles.^[2]

M. howittii is endemic to Banks Peninsula in the Canterbury region of the South Island. The species is only known to occur in the central and eastern parts of the peninsula, although historical records it they used to occur as far west as the Port Hills. It is possible this range contraction is due to nineteenth-century deforestation and predation by introduced mammals. They can be found at both lowland and higher altitudes.^[3]

They are known to occur in podocarp and hardwood forest remnants, and grassland (and are apparently most common in the latter), but can also be found even in heavily-modified habitat such as pasture.^[3][8] The distribution of this burrowing species is linked with the presence of fallen logs to hide under, and it is more common in areas with more logs and less disturbance.^[3][4]

M. howittii is most active during spring and summer months (when it apparently breeds), being most common in November. Gravid females have been observed from December to January.^[4] This is a common activity pattern for other Banks Peninsula carabids.^[4]

These beetles are nocturnal, but can be seen during the day in some conditions.^[8][4] Like most crabids, they are active predators, observed preying on the larvae of Holcaspis suteri, crane flies, and Tenebrio molitor (in captivity).^[9] They are thought to be less active when soil temperatures are below 6.5°C and are also known to be slow runners.^[4][8]

Native predators are presumed to include the morepork, large species of spider, and weka (although this species is no longer present on the peninsula).^[9] They are probably preyed upon by introduced mammalian predators.^[3] An undescribed species of mite from the genus Micromegistus has been associated with M. howittii; these mites primarily latch onto the pronotal and metasternum areas and are most common around the coxae.^[9]

Under the New Zealand Threat Classification System, this species is listed as "Declining" with the qualifiers of "Range Restricted" and "Sparse".^[10] It has a fragmented range in eastern and central Banks Peninsula, which may still be contracting.^[3]

• iNaturalist observations of M. howittii