tau emerald

The tau emerald is a medium-sized, black and yellow dragonfly with long legs,{{Cite book|title=The Australian Dragonflies: A Guide to the Identification, Distributions and Habitats of Australian Odonata|last1=Watson|first1=J.A.L.|last2=Theischinger|first2=G.|last3=Abbey|first3=H.M.|publisher=CSIRO|year=1991|isbn=0643051368|location=Melbourne}}

reaching a body length of about 50 mm.{{Cite web|title=Tau Emerald Dragonfly - Hemicordulia tau|url=http://www.brisbaneinsects.com/brisbane_dragons/TMark.htm|access-date=2021-06-17|website=www.brisbaneinsects.com}} As is unique to dragonfly and mayfly species, H. tau has flight muscles attached directly to the wings,{{Cite journal|last1=Devi|first1=M.|last2=Indirakumar|first2=K.|date=2020|title=Why Insects are Dominance in the Biosphere?|url=https://bioticainternational.com/ojs/index.php/biorestoday/article/view/564|journal=Biotica Research Today|language=en-US|volume=2|issue=11|pages=1174–1178|issn=2582-6654}} 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.{{Cite book|author1=Theischinger, G.|author2=Endersby, I.|url=http://worldcat.org/oclc/535321248|title=Identification guide to the Australian Odonata|date=2009|publisher=Dept. of Environment, Climate Change and Water|isbn=978-1-74232-475-3|oclc=535321248}} 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.{{Cite web|last=Zielinski|first=Sarah|title=14 Fun Facts About Dragonflies|url=https://www.smithsonianmag.com/science-nature/14-fun-facts-about-dragonflies-96882693/|access-date=2021-06-14|website=Smithsonian Magazine|language=en}} H. tau has a particularly large and well developed compound eye with two principal regions, the dorsal eye and the ventral eye.{{Cite journal|last1=Yang|first1=E.C.|last2=Osorio|first2=D.|date=1996|title=Spectral responses and chromatic processing in the dragonfly lamina|url=http://link.springer.com/10.1007/BF00190184|journal=Journal of Comparative Physiology A|language=en|volume=178|issue=4|doi=10.1007/BF00190184|s2cid=24838606|issn=0340-7594|url-access=subscription}} 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 of the water it inhabits increases. It is capable of completing its life cycle from egg to adult in less than 6 weeks.{{Cite web|title=Odonata {{!}} What Bug Is That?|url=http://anic.ento.csiro.au/insectfamilies/biota_details.aspx?OrderID=24130&BiotaID=40294&PageID=families|access-date=2021-06-17|website=anic.ento.csiro.au}} Nymphs reach a total length of 22–24 mm. No mid-dorsal abdominal spines are present unlike other Hemicordulia, but humps may be present on segments 4–9 and the lateral spines are very small.{{Cite book|last=Theischinger|first=G.|url=https://www.worldcat.org/oclc/1252724816|title=The complete field guide to dragonflies of Australia|date=2006|others=John Hawking|isbn=978-1-4863-1375-4|publisher=Csiro Publishing|location=Collingwood, Vic.|oclc=1252724816}} The nymphs have a ladle-shaped labium with premental and palpal setae, and well-developed palpal dentations bearing groups of setae. The prementum has a distinct ventro-basal midline/groove.

An analysis of head width frequencies of samples from Lake Eucumbene suggest there is at least 9 instars in the life history of H. tau, however the number of larval instars is known to vary between, and within, Odonata species.

H. tau is found in all parts of Australia except northern Queensland and north-western Western Australia{{cite book|title=The Complete Field Guide To Dragonflies Of Australia|year=2006|publisher=CSIRO Publishing|location=Collingwood, Victoria|pages=249|author1=Günther Theischinger|author2=John Hawking}} and is one of Australia's most abundant dragonflies.{{Cite journal|last=Faragher|first=R. A.|date=1980|title=Life Cycle of Hemicordulia Tau Selys (odonata: Corduliidae) in Lake Eucumbene, N.S.W., with Notes on Predation on It by Two Trout Species|journal=Australian Journal of Entomology|language=en|volume=19|issue=4|pages=269–276|doi=10.1111/j.1440-6055.1980.tb00985.x|issn=1440-6055|doi-access=free}} It is considered a dry-country dragon fly, often inhabiting the arid Australian inland.{{Cite journal|last=Watson|first=J.A.L.|date=1982|title=Dragonflies in the Australian environment: taxonomy, biology and conservation|url=https://natuurtijdschriften.nl/pub/593043|journal=Advances in Odonatology|language=en|volume=1|issue=1|pages=293–302|issn=0168-0161}} The adults are vagrants and highly opportunistic users of habitat for breeding.

In addition to rivers, lakes and swamps H. tau has the ability to breed in temporary waters due to its short larval stages.{{Cite journal|last1=Hodgkin|first1=E. P.|last2=Watson|first2=J.A.L.|date=1958|title=Breeding of Dragonflies in Temporary Waters|url=https://www.nature.com/articles/1811015b0|journal=Nature|language=en|volume=181|issue=4614|pages=1015–1016|bibcode=1958Natur.181.1015H|doi=10.1038/1811015b0|issn=1476-4687|s2cid=4272949|url-access=subscription}} Nymph have a high thermal growth coefficient and details of its life history may vary with their location. The nymph are able to tolerate the high temperatures found in temporary shallow ponds. 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. They are also able to overwinter in cold permanent refuges, and have been observed in water with a salinity between 7.8g/L to 13.9g/L.{{Cite journal|last1=Rutherford|first1=J.C.|last2=Kefford|first2=B.J.|year=2005|title=Effects of salinity on stream ecosystems: improving models for macroinvertebrates|url=https://publications.csiro.au/publications/publication/PIprocite:c0930011-a85c-470f-aaa5-d579380600aa|journal=CSIRO Land and Water Technical Report|doi=10.4225/08/58597507b8552|access-date=2021-06-14}}

H. tau larva, similar to other Odonata species, are associated with clean water and it has been suggested they could be monitored to detect changes in water quality. Larval habitat is typically leaf litter and weeds. Many aquatic invertebrates with terrestrial adult stages require a snag extending above the water surface for emergence to the adult stage.{{Cite journal|last=Davies|first=Peter|date=1998|title=Large woody debris are important habitat in rivers.|url=https://wetlandresearch.com.au/wp-content/uploads/2014/08/Davies-Storey-LWD-1998.pdf|journal=Western Wildlife|volume=2|pages=14–15|via=Wetland Research}}

Predators primarily include fish and birds.{{Cite journal|last=Lenz|first=Michael|date=2018|title=Mass Emergence of Dragonflies Attract Large Numbers of White-Faced Herons|url=http://canberrabirds.org.au/wp-content/uploads/2018/12/CBN-43-3-final.pdf|journal=Canberra Bird Notes|volume=43|pages=290–293|via=Canberra Ornithologists Group}}

The tau emerald is listed as least concern under the International Union for Conservation of Nature and Natural Resources (IUCN) red list of threatened species.{{Cite web|last=Dow|first=R.A.|date=2017|title=IUCN Red List of Threatened Species: Hemicordulia tau|url=https://www.iucnredlist.org/en|access-date=2021-06-16|website=IUCN Red List of Threatened Species}} Population trend is classified as unknown and no conservation actions are recommended.

File:Tau Emerald Dragonfly - Flickr - jeans Photos (2).jpg|Tau Emerald Dragonfly

Tau Emerald inflight edit.jpg|Male in flight

Hemicordulia tau (12167423046).jpg|Female

Hemicordulia tau (15907938856).jpg|Female

Hemicordulia tau male 2.jpg|Male

Tau emerald dragonflies mating.jpg|Mating pair

Hemicordulia tau female wings (34248911003).jpg|Female wings

Hemicordulia tau male wings (34248917153).jpg|Male wings

File:Hemicordulia tau (5119858240).jpg|Hemicordulia tau

File:Hemicordulia tau in flight.jpg|Hemicordulia tau in flight

File:Hemicordulia tau dipping tail.jpg|Hemicordulia tau dipping tail

File:Hemicordulia tau.jpg|Hemicordulia tau

{{Commons|Hemicordulia tau}}

{{Wikispecies|Hemicordulia tau}}

{{Reflist}}

{{Taxonbar|from=Q2471088 }}

Category:Corduliidae

Category:Insects of Australia

Category:Endemic fauna of Australia

Category:Insects described in 1871