Hemicordulia tau
In 3 days ~20% 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 Sydney on a given day, based on 176 verified sightings from GBIF citizen-science data. It is the 81st most-seen of the 742 insects we can rate there. Over three days the chance rises to about 20%, and over a week to about 50%, if each day is a fresh chance.
September
In that month about 20% of wildlife watchers report a Tau Emerald in Sydney on a given day, against under 5% in May–July and December–March, the lowest months. That is one of Sydney's driest months, with about 45 mm of rain against 130 mm in February.
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.
3rd of 4
Of the 4 cities where we can rate Tau Emerald sightings, Sydney ranks 3rd at about 10%. The best odds are in Melbourne (Australia, about 20%) and Perth (Australia, about 10%).
GBIF citizen-science records
It is estimated from how often the Tau Emerald is recorded against all the insects logged in Sydney (176 verified sightings), 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.
