Genus Tetrathemis

 

The genus Tetrathemis includes two very small species (hw, 18-21 mm): :

Tetrathemis irregularis  It is common and  widespread in lowland swamp forest and sluggish forest streams, particularly in more disturbed areas, but is quite local. It is found at altitudes up to 500 m. Males guard tiny pools and remain perched on station for most of the day. Tetrathemis irregularis eyes are a strikingly brilliant blue/green.

Tetrathemis flavescens is rarer, and may be distinguished by an extensive basal yellow suffusion best developed in the hind wing. Risiophlebia dohrni (Plate 19b, Fig. 157) is of similar appearance and size but can be recognized at a glance by its enormously expanded second abdominal segment, which in the male bears the secondary sexual apparatus. However even in the female the second segment is strongly swollen and distinguishable at a glance from Tetrathemis. It is a common but local inhabitant of peat swamp and alluvial forest, hovering over tiny ponds in shafts of sunlight penetrating the canopy.

Both Tetrathemis and Risiophlebia are placed in the subfamily Tetrathemistinae because the forewing discoidal triangle is in fact a well defined quadrilateral. However this is not very evident in Risiophlebia and the condition occurs to some extent in many other genera in other subfamilies. Also in this group is the scarce Hylaeothemis dementia, another small black and yellow species. It inhabits alluvial swamps in the lowlands.

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INDEX OF DRAGONFLY