[2] The tau emerald is a medium-sized, black and yellow dragonfly with long legs,[4] reaching a body length of about 50 mm.

[5] As is unique to dragonfly and mayfly species, H. tau has flight muscles attached directly to the wings,[6] and in both the males and females the inboard edge of the hindwing is rounded.

[11] The length of time each larval stage of H. tau requires can decrease as the temperature of the water it inhabits increases.

[9] In addition to rivers, lakes and swamps[8] H. tau has the ability to breed in temporary waters due to its short larval stages.

[15] Nymph have a high thermal growth coefficient and details of its life history may vary with their location.

[9] The ability of H. tau to utilize temporary waters and reduce its larval life with increase in temperature contribute to its abundance and wide distribution.