Nesiobius gracilis is a weevil species endemic to the island of St Helena, present in the high altitude cloud forests. In its indigenous habitat it has been found under the bark and in dead wood of endemic Cabbage trees: Black Cabbage Tree (Melanodendron integrifolium – Vulnerable), She-cabbage (Lachanodes arborea – Extinct in the Wild) and He-cabbage (Pladaroxylon leucodendron – Critically Endangered) (Lambdon and Ellick 2016)) and from beating St Helena Dogwood (Nesohedyotis arborea – Critically Endangered) (Lambdon and Ellick 2016), but it has also been found in the dead wood of Thorn Tree (Erythrina caffra), which is widely planted around the island. One hundred and one specimens were collected between 1966 and 1967 during extensive survey work on the island. Specimens were recorded from five sites surveyed by Mendel, Ashmole and Ashmole in 2005–2006 (Mendel et al. 2008) and Pryce (2021) recorded five specimens from three sites in 2016.

There are challenges associated with identification within this genus. This species is not restricted to the cloud forest. Populations in the cloud forest are under threat from climate change, invasive non-native species of trees and shrubs, as well as New Zealand Flax (Phormium tenax) (impacting host trees), invasive non-native invertebrates, and the recent spread of fungal diseases, including Phytophthora spp., on cloud forest trees will seriously threaten this species. Populations present on non-native plant species are under threat from habitat deterioration and loss from drivers of change including climate change. Non-native vertebrate predators, such as rodents and the African Grass Frog (Strongylopus grayi) may also negatively impact this species. Its extent of occurrence (EOO) and area of occupancy (AOO) are both 20 km², it is only known from a single location (from multiple sites but only one area of habitat affected by the same threat processes of invasive species and climate change), and there is continuing decline in habitat due to the threats described above. Further survey work is required for this species. Meanwhile, this species is assessed as Critically Endangered

Nesiobius gracilis is a weevil endemic to the island of St Helena, in the South Atlantic. This species is recorded from high altitudes on the island. This species was commonly collected at high elevations by Wollaston from between Grapevine Gut and up to Cuckold's Point/Mt. Actaeon/Diana’s Peak and along Stitch’s Ridge. It was also recorded from Halley's Mount. Thirty four specimens from H Roberts collection are in the British Museum. Surveys in the 1960s collected 101 specimens of this species from the High Central Ridge, Rural Retreat Gut, Upper Fisher’s Valley, Cason’s Gate, and High Peak. Surveys in 2005–2006 collected specimens of this species from Cuckold’s Point, Cabbage Tree Road, Osborne’s (She cabbages), High Peak and Mount Vesey. In 2016, five specimens were collected by Pryce (2021) from three sites from hand searching and Berlese extraction from dead wood and leaf litter.

Note: there are historical changes with the site names for Diana’s Peak, Cuckhold’s Point and Mt Actaeon and as such, we are including all the names in this assessment for the location of the records; see St Helena Government (2020).

This species was commonly collected at high elevations by Wollaston from between Grapevine Gut and up to Diana’s Peak, Actaeon and along Stitch’s Ridge. In the 1960s 101 specimens of this species were collected from the High Central Ridge, Rural Retreat Gut, Upper Fisher’s Valley, Cason’s Gate, and High Peak. In 2016, five specimens were collected by Pryce (2021) from three sites from hand searching and Berlese extraction from dead wood and leaf litter.

Wollaston considered this species to be associated with endemic Cabbage trees: Black Cabbage Tree (Melanodendron integrifolium, assessed as Vulnerable), She-cabbage (Lachanodes arborea, assessed as Extinct in the Wild) and He-cabbage (Pladaroxylon leucodendron, assessed as Critically Endangered) (Lambdon and Ellick 2016). Surveys in the 1960s recorded this species from Cabbage trees but also other native and non-native species, such as Thorn tree (Erythrina caffra), under the bark and dead wood of Cabbage trees and from beating St Helena Dogwood (Nesohedyotis arborea, assessed as Critically Endangered) (Lambdon and Ellick 2016).

This species was last recorded in 2006 in the cloud forest on endemic species such as Cabbage trees, but also on non-native species such as Thorn tree (Erythina caffra). The cloud forest host trees have ongoing threats including climate change, intense competition from invasive non-native plant trees, shrubs and other plant species, including New Zealand Flax (Phormium tenax). The recent arrival and spread of fungal tree diseases, including Phytophthora spp., on cloud forest trees, will seriously threaten this species, although this may be preceded by a temporary boom in the beetles’ population if a large number of endemic trees die and decay, likely followed by a disastrous collapse. Species of non-native predatory invertebrates living in decaying wood, such as ants, rove beetles, spiders and centipedes, and saproxylic species that modify the dead wood habitat, such as powder-post beetles, millipedes and woodlice, are likely to impact this species negatively. Populations present on non-native plant species are under threat from habitat deterioration and loss from drivers of change including climate change. Non-native vertebrate predators, such as rodents and the African Grass Frog (Strongylopus grayi) may also negatively impact this species.

This species is on the Environmental Protection Ordinance on St Helena, which indicates protected species. The Peaks are currently within a protected area and part of the government’s Nature Conservation Area (NCAs). This species will benefit from the habitat improvement outlined in the Peaks National Park Management Plan (2019). There is currently no specific action plan for this species, but its conservation and further research will be supported through the St Helena Invertebrate Strategy 2023–2027 (St Helena National Trust and St Helena Government 2023).