Mackenzie's Most Wanted

In the early autumn weeks in the Mackenzie Basin, Canterbury, the array of life that is so present in summer begins to dwindle. As it seems that all life forms have finished blooming and arising from the earth, a small moth begins to emerge from its hidden cocoon, to begins its adult life. It lives in the mix of rank and dry grasses along the Haldon Road, near where the Grays River flows. Locally, it is abundant, with large gatherings of these moths resting on the grasses, moving like flaky skin when disturbed. This is Orocrambus fugitivellus, a small grass moth endemic to the Mackenzie Basin. It is considered rare as it is specifically only seen here, along the Grays River and surrounding lands. They flutter laboriously, with short little wings and a small body.

So, what’s so special about this small moth? Firstly, it’s only found in this area of the Mackenzie Basin, which is a very small area. Secondly, it is a relatively new species to science, only being named in the 1950s – by George V. Hudson, from the grave as the species was included in the publication called Fragments of New Zealand Entomology. Hudson died before he got the chance to name the species, however his family published the last of his unfinished work after his death. Orocrambus fugitivellus is one of them. The specific name, fugitivellus, comes from the word “fugitive” – referring to James Mackenzie, the infamous sheep stealer who went on the run through Canterbury in the 1850s – where after the Mackenzie Basin was named after him. Orocrambus, the genus of O. fugitivellus, is completely endemic to New Zealand and are known as the New Zealand grass moths – as they are generally associated with the grasses their caterpillars depend on for food. Currently 52 species are described and are found in a range of different habitats, such as lowland grasslands, sub-alpine and alpine tussock grasslands, bogs, swamps and slow-flowing streams.

The area where Orocrambus fugitivellus is found is a mix of dry and wetlands, with the reserve we visited, Glen Rock Conservation Area, being quite dry in early March, due to the lack of the rain that summer. Regardless of the drought, the moth was exceedingly abundant, seemingly pouring out of grass swards when disturbed. This area, along the Haldon Road and opposite the Grays River, is quite simple in vegetative composition. A matrix of exotic and native grass dominates, with some relic native shrubs scattered about. Some of these shrubs, such as Olearia odorata, were evidently grazed by livestock. On a nearby hill, small boulders are present, with dryland lichens and mosses inhabiting this space. Other lepidoptera fauna in the area include Lycaena tama, the Canterbury alpine boulder copper, other Orocrambus species such as O. vulgaris, O. lewisii/ordishi and the currently undescribed species, O. “mk” – first noted in the area in the 1990s and also endemic to the basin. Some other endemic moth species here seen flying in March were Tawhitia pentadactylus and Asaphodes abrogata.

It is most important for the survival of this species and others like it, to conserve adequate habitat. Unfortunately, questions about Orocrambus fugitivellus are still left unanswered. The primary host plant of the species is not known – it is assumed to be some sort of grass, but the caterpillar has never been observed. Sometimes endemic moths even depend on exotic grasses for nutrition at the caterpillar stage. So, study needs to be done on various habitat types around the Grays River and where it is most likely to encounter this moth. It is peculiar that this species is only found around this part of the Mackenzie Basin. What makes this specific area suitable for this moth? The female adult, although we did not see it, is apparently flightless with reduced wings (brachypterous). How does this affect the distributional limits of the species? The Glen Rock Conservation Area seemed to host a strong population of these moths, but management of loose stock, potential weed threats and adequate access to the reserve needs to be addressed. If habitat can be adequately conserved, and some more questions answered – the species could be steadily conserved and cherished as a characteristic species of this landscape. Hopefully next season and seasons to come, this fugitive moth can be caught on the wing yet again.

Posted on May 26, 2024 11:00 PM by noahfenwick