Blue Riverjack (Metacnemis valida)

Blue Riverjack, Metacnemis valida, Blourivierjuffer

Short description:

Blue Riverjack, Metacnemis valida, Blourivierjuffer is medium sized, stout, strikingly primarily pale blue, with black stripes on thorax, and conspicuous black rings on abdomen.

Also known as Kubusi Streamjack or Blue Streamjack

Family Platycnemididae (Yakobson & Bianchi, 1905 Stream Damsels)

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Male

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Key identification features:

Male:

Face dull black with a little brown. Labrum pale blue dull black with a little brown. Labrum pale blue with a central black spot. Anteclypeus grey. Postclypeus grey with two lateral streaks. Head above, black Neck pale blue with wide central black stripe.
Eyes dull pale blue, with some brown
Thorax pale blue, strongly marked with narrow black stripes.
Wings clear with black veins. Pterostigmas light brown, almost square in shape.
Segments 2 to 6 with striking incomplete black rings against light blue background. Segment 7 with black stripe running along top. Segments 8 to 10 with fine black rings against light blue. Segments 8 and 9 with small black spots on either side. Superior appendages long, black.

Female:

Patterning similar to male.
Eyes light brown above with distinct brown light brown lower margin.
Black is replaced by brown black, pale blue not so vivid, except lower half of synthorax
Strong pale white/light brown stripe running across side of thorax;
Abdomen with brown saddle-like markings at hind margin of segment. S 9-10 distinctly bulbous
Thorax has light brown white stripe wat lower thorax. Dorsal thorax greenish brown with dark brow dorsal carina stripe
Head, neck,thorax and segments 9 to 10 greenish brown above.

Habitat:

Rivers and streams in open landscapes, but sometimes shaded by gallery forest. Usually with rocks and probably often submerged roots and/or dead trunks or branches.
Inferred to occur from 0 to 1400 m above sea level.

Behaviour:

Powerful flyer that hawks out over fast flowing rivers or stream

Compared with other species:

Colouration, stout body, and its short pterostigmas make this species unmistakable
Only in the ECP, with few records from southern KZN
Spesbona angusta (Spesbona) is much lighter blue than, and much larger and more robust.
Mesocnemis singularis (Savanna Riverjack) has similar behaviour, but is all pale blue,distinctly pruinescent, and inhabits savanna rivers.
Blue bands on abdomen may be similar to Africallagma sapphirinum, (Sapphire Bluet)

Distribution

South Africa:

Endemic to South Africa.
ECP, with few records from southern KZN. The species may be more abundant as previously assumed More records required