Blue Riverjack (Metacnemis valida)

View the above photo record (by Stewart Bruce MacLachlan) in OdonataMAP here.

Find the Blue Riverjack in the FBIS database (Freshwater Biodiversity Information System) here.

Family Platycnemididae

Metacnemis validaBLUE RIVERJACK

Identification

Medium sized with a robust build.

Length reaches 41mm; Wingspan attains 56mm.

Unlike any other South African species. Males are strikingly coloured in bright blue with bold black bands and stripes.

Males are distinctive and easily identified. Females are similar to those of Mesocnemis singularis (Savanna Riverjack), but that species lacks the pale diagonal band on the sides of the thorax. The two species are not known to co-occur.

Click here for more details on identification.

Metacnemis valida – Male
Near Port Elizabeth, Eastern Cape
Photo by Andre Marais

Habitat

The Blue Riverjack has a preference for rocky, fast-flowing rivers and streams. It requires clean, clear and shallow water with an abundance of rocks.

Behaviour

Perches on rocks, close to the waters edge in exposed sunny locations. Less often on overhanging or emergent plant stems. Often sits in the midstream and the females are frequently found alongside the males. Flies low and fast over the water.

Most active from November to March (See Phenology below).

Status and Conservation

Metacnemis valida is rare and localised. It is listed as Endangered in the IUCN Red List of Threatened Species. The Blue Riverjack is not tolerant of habitat degredation. It is severely threatened by habitat loss within its restricted distribution. Negative impacts on its habitat include turbid water from soil erosion and copses of alien trees along the river banks that shade out rivers.

Distribution

It is endemic to the Eastern Cape province of South Africa. Ranges from near Humansdorp in the South to Bizana in the north.

Below is a map showing the distribution of records for Blue Riverjack in the OdonataMAP database as at February 2020.

The next map below is an imputed map, produced by an interpolation algorithm, which attempts to generate a full distribution map from the partial information in the map above. This map will be improved by the submission of records to the OdonataMAP section of the Virtual Museum.

Ultimately, we will produce a series of maps for all the odonata species in the region. The current algorithm is a new algorithm. The objective is mainly to produce “smoothed” maps that could go into a field guide for odonata. This basic version of the algorithm (as mapped above) does not make use of “explanatory variables” (e.g. altitude, terrain roughness, presence of freshwater — we will be producing maps that take these variables into account soon). Currently, it only makes use of the OdonataMAP records for the species being mapped, as well as all the other records of all other species. The basic maps are “optimistic” and will generally show ranges to be larger than what they probably are.

These maps use the data in the OdonataMAP section of the Virtual Museum, and also the database assembled by the previous JRS funded project, which was led by Professor Michael Samways and Dr KD Dijkstra.

Phenology

Dragonfly Atlas: Megan Loftie-Eaton, Sally Hofmeyr, Ryan Tippett & Les Underhill
Dragonfly Atlas: Megan Loftie-Eaton, Sally Hofmeyr, Ryan Tippett & Les Underhill
Megan Loftie-Eaton is our communications, social media and citizen science coordinator. Prior to her work for the BDI, she coordinated OdonataMAP, the Atlas of African Odonata. Sally Hofmeyr has many years' experience in the academic world, writing her own material and editing the work of others. Her academic background is in the natural sciences: her PhD and first postdoc in ornithology and environmental change (Animal Demography Unit, University of Cape Town). Ryan Tippett is an enthusiastic contributor to Citizen Science and has added many important and interesting records of fauna and flora. He has been a member of the VMU since 2014 and has currently submitted over 11000 records. He is also on the expert identification panel for the Odonata Map project. Prof Les Underhill has been Director of the Animal Demography Unit (ADU) at the University of Cape Town since it started in 1991. Although citizen science in biology is Les’s passion, his academic background is in mathematical statistics.