Tetracanthagyna waterhousei McLachlan, 1898

A female resting under a large leaf, at Ba Vi NP. A perfect umbrella.

Tetracanthagyna waterhousei is a dragonfly of great size and robust build, equalling in this respect the largest known living dragonflies. It is known to be crepuscular, coming out in forest after sunset – as many Aeshnids. But all the females I spotted were well active during the day. The male have hitherto eluded me. 

Female, Tam Dao.

T. waterhousei is one of the 4 Aeshnids I encountered the most in the Hanoi area (sensu lato, i.e. within a 60-70 km radius) - with Gynacantha subinterrupta, Anax guttatus and Polycanthagyna erythromelas. As the latter, T. waterhousei is a strict forest stream dweller. 

The two sexes are similar in appearance. Both have dark reddish-brown abdomen and thorax, the latter marked with bright citron-yellow as follows : oblique narrow antehumeral stripes converging strongly on mid-dorsal carina, two rather broad stripes on each side, the anterior close to the humeral suture, the posterior traversing the middle of metepimeron and broadest of the two. 

Note the head very massive, globular, the eyes very broadly contiguous, the face warm brown, the frons not elevated and blackish on upper surface.

Female have a short, cylindrical, very robust abdomen, but tapering very gradually towards the anal end. Segments 2 to 7 with very narrow yellowish apical annules, narrowly interrupted on mid-dorsum; S8-10 unmarked. 

End of abdomen, female.

Ovipositor is very massive, extending nearly to end of abdomen ; segment 9 with the apical dorsal spine more robust than in the male; segment 10 prolonged into a 4-spined dentigerous plate below, the two medial spines longer than the others.

This dentigerous plate is an adaptation to enable the insect to oviposit in dry soil, the robust pitchfork-shaped organ being employed to scoop holes or to fix the end of the abdomen whilst the ovipositor is driven home in the ground. This habit is shared by many other Aeshnids. 
The female deposits her eggs in mud or dry soil along streams. I also spotted it ovipositing in branches.

A female resting after ovipositing.

Female ovipositing in a (dead?) branch, 5-6 meters above a stream (you can clearly see the ovipositor protruding).

T. waterhousei is widely distributed in tropical and subtropical mainland Asia, with records from eastern India to Laos, Vietnam and southern China.

I encountered this gorgeous species in both pristine forest (Cuc Phuong NP) and degraded secondary forest (first slopes of Mount Ba Vi and Tam Dao); it don't seem too fussy.

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