Australian Emerald and Tau Emerald Dragonfly: A Comparison

Tau Emerald Dragonfly
Hemicordulia australiaeBrownish eyes
Inverted T mark on the frons
Orangish leading veins on coastal margin
Brown pterostigma
Yellow mark on 10th abdominal segment
Black 7th abdominal segment

Location: South Western Australia

Season: Summer, December

Order: Odonata 

Family: Corduliidae 

Genus: Hemicordulia 

Hemicordulia Tau

Hemicordulia is a common species of dragonflies in Australia. Australian Emerald Dragonfly, H. australiae and Tau Emerald, H. tau are a bit tricky to distinguish in the field. However, I have learnt a few pointers towards identification. 

Similarities:

Size: Both are medium sized dragonflies, about 5 to 6 cms in length.

Perching pattern: H. tau and H. australiae both perch similarly. They hang on to the tip of the branches perpendicular to the ground. This feature makes it easy to distinguish the Hemicordulia dragonflies from other yellow dragonflies such as female Blue Skimmers, Yellow Striped Hunters which rest parallel to the ground. 

Hemicodulia species perch on higher branches and settle there for longer periods.

 Abdominal markings: Both have metallic dark green pattern over orangish yellow colour. This colour shines brilliantly in sunlight giving the name Emerald. The thorax is yellowish grey. 

Differences between H. australiae and H. tau 

Eyes: Mature H. australiae has bright greenish blue eyes that dazzle in the sunlight. H. tau has brownish eyes. 

Abdomen: H. tau has a yellow spot on the 10th abdominal segment (tip of the tail)

The seventh abdominal segment is darkly coloured in H. tau whereas the yellow marking is present in H. asutraliae.

Head: Inverted T shaped mark on H. tau is the telltale feature, hence the name. This is not present on H. australiae.

Wings: H. australiae has clear wings. The veins are black.

H. tau has brownish red to orange leading viens. The pterostigma is brown. 

Again, I present you with a not-so-spectacular image of H. australiae. It is about time I got a better picture of the Emerald, but some features are still remarkable in the photo below.

Australian Emerald
Hemicordulia asutraliae
Bright greenish blue eyes
No T mark on the frons
Clear wings with black veins.
Black/clear pterostigma
7th abdominal segment has yellow/orange marking

Reference: Wiki, Ecology Solutions, Esperance Fauna