BackPolydesmus ribeiraensis Demange, 1970

Polydesmus ribeiraensis Demange, 1970


  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Diplopoda
  • Order: Polydesmida
  • Family: Polydesmidae
CR Critically Endangered
IUCN Red List Status:

Countries of Occurrence:
Portugal - Azores


Russell, N.


Facilitators / Compilers/s:

Assessment Rationale:

Polydesmus ribeiraensis is endemic to Sao Miguel (Azores, Portugal). It has a very small Extent of Occurrence (EOO = 16 km²) and Area of Occupancy (AOO = 16 km²). There is a continuing decline in the EOO, AOO, extent and quality of habitat as well as the number of mature individuals as a result of the invasions of non-native plants and displacement by exotic millipedes. Increasing tourism in the island might also impact its habitat, being a scenic destination. The species occurs only at one location, and so it is assessed as Critically Endangered (CR). We suggest as future measures of conservation: (1) regular monitoring of the species; (2) control of invasive species namely Hedychium gardnerianum, and (3) measures to mitigate possible impacts from increasing tourism. 

Geographic Range:

Polydesmus ribeiraensis is a single-island endemic millipede species restricted to S. Miguel island (Azores, Portugal) (Borges et al. 2010), known from a single disturbed location. The Extent of Occurrence (EOO) is 16 km² and the maximum estimated Area of Occupancy (AOO) is 16 km².

Portugal - Azores
Extent of Occurrence (EOO):
16 (km2)
Area of Occupancy (AOO):
16 (km2)
Elevation Lower Limit:
10 (m)
Elevation Upper Limit:
300 (m)
Biogeographic Realms:
Endemic Azores


The species is very rare and only known from a single subpopulation. A continuing decline in the number of mature individuals is inferred from the ongoing habitat degradation due to invasions of alien plants (Hedychium gardnerianum) and other arthropods (Ommatoithus moreletii).

Current Population Trend: Decreasing 

Habitat and Ecology

Little is known of the ecology and traits of this species. It is present in the moist soil and leaf litter in Ribeira Quente, a valley with streams and rivulets of geothermal origin. This area is degraded and under threat by invasive plant species and human activities.

Systems: Terrestrial

Major Threat(s):

In the past, the species has probably strongly declined due to major historical land use changes in surrounding areas. The most important ongoing threat to this species is the spread of invasive plants (Hedychium gardnerianum) which are changing the habitat and soil structure, and displacement by invasive millipede species like Ommatoithus moreletii. Human activities like tourism and urbanisation are also affecting part of the habitat. Based on Ferreira et al. (2016) the habitat quality will also decline as a consequence of climate change (increasing number of droughts, and habitat shifting and alteration). 

Conservation Actions

The species is not protected by regional law, but its habitat is partially in a regionally protected area (Natural Park of S. Miguel). Degraded habitats should be restored and a strategy needs to be developed to address the future threat from climate change. A habitat management plan is needed and one is anticipated to be developed during the coming years. Education and awareness is also needed to avoid negative impacts of touristic activities. Further research is needed into its ecology and life history and to obtain information on population size, distribution and trends; and it is also necessary to develop an area-based management plan and a monitoring plan for the invertebrate community in this habitat in aid in the production of a potential species recovery plan. Monitoring every ten years using the BALA protocol will inform about habitat quality (see e.g. Gaspar et al. 2011).