Hemicordulia tau
In 3 days ~30% in a week ~50%
The tau emerald (Hemicordulia tau) is a species of dragonfly in the family Corduliidae. The species was first described by Edmond de Sélys Longchamps in 1871. The tau emerald is a medium-sized, black and yellow dragonfly with long legs,
reaching a body length of about 50 mm. As is unique to dragonfly and mayfly species, H. tau has flight muscles attached directly to the wings, and in both the males and females the inboard edge of the hindwing is rounded. The 7th abdominal tergum is extensively black above and yellowish at the sides. The top of the frons are yellow with a dark T-mark. The species exhibits a linear relationship between head width and body length.
Nearly all of the dragonfly's head is eye, allowing incredible vision that encompasses almost every angle except right behind them. H. tau has a particularly large and well developed compound eye with two principal regions, the dorsal eye and the ventral eye. The dorsal eye is principally sensitive to short wavelength light, while the ventral eye has 3 or more spectral types of photoreceptors.
The length of time each larval stage of H. tau requires can decrease as the temperature... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Grampians National Park | 🇦🇺 Australia | |
| 2 | Hattah-Kulkyne National Park | 🇦🇺 Australia | |
| 3 | Great Otway National Park | 🇦🇺 Australia | |
| 4 | Flinders Ranges National Park | 🇦🇺 Australia | |
| 5 | Booderee National Park | 🇦🇺 Australia | |
| 6 | Kosciuszko National Park | 🇦🇺 Australia | |
| 7 | Wilsons Promontory National Park | 🇦🇺 Australia | |
| 8 | Blue Mountains National Park | 🇦🇺 Australia | |
| 9 | Royal National Park | 🇦🇺 Australia |
With luck
About 10% of wildlife watchers report a Tau Emerald sighting in Wilsons Promontory National Park on a given day, based on 5 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 50th most-seen of the 60 insects we can rate there. Over three days the chance rises to about 30%, and over a week to about 50%, if each day is a fresh chance.
January and October
In those months about 20% of wildlife watchers report a Tau Emerald in Wilsons Promontory National Park on a given day, against under 5% in March–September and November, the lowest months.
Between noon and 3 pm
Across all the parks we cover, that three-hour window holds the most Tau Emerald sightings with a recorded time, and about 9 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
7th of 9
Of the 9 parks where we can rate Tau Emerald sightings, Wilsons Promontory National Park ranks 7th at about 10%. The best odds are in Grampians National Park (Australia, about 30%), Hattah-Kulkyne National Park (Australia, about 30%) and Great Otway National Park (Australia, about 20%).
Same order: Odonata
The closest relatives of the Tau Emerald that you can see in Wilsons Promontory National Park (order Odonata, Dragonflies and Damselflies) are Common Flatwing (about 20%), Multi-Spotted Darner (about 10%) and Southern Tigertail (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Tau Emerald is recorded against all the insects logged in Wilsons Promontory National Park (5 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
