Tau emerald
Male
Female
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Odonata
Infraorder: Anisoptera
Family: Corduliidae
Genus: Hemicordulia
Species:
H. tau
Binomial name
Hemicordulia tau
(Selys, 1871)[2]

The tau emerald (Hemicordulia tau) is a species of dragonfly in the family Corduliidae.[3] Corduliidae is the only family not a clade within the Infraorder Anisoptera. The species was first described by Edmond de Sélys Longchamps in 1871.[2]

Description

Adult

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.[4] The 7th abdominal tergum is extensively black above and yellowish at the sides.[7] The top of the frons are yellow with a dark T-mark.[8] The species exhibits a linear relationship between head width and body length. [9]

Nearly all of the dragonfly's head is eye, allowing incredible vision that encompasses almost every angle except right behind them.[10] H. tau has a particularly large and well developed compound eye with two principal regions, the dorsal eye and the ventral eye.[11] The dorsal eye is principally sensitive to short wavelength light, while the ventral eye has 3 or more spectral types of photoreceptors.[11]

Larval stages

The length of time each larval stage of H. tau requires can decrease as the temperature of the water it inhabits increases.[9] It is capable of completing its life cycle from egg to adult in less than 6 weeks.[12] 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.[13] 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.[8]

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.[9]

Ecology

H. tau is found in all parts of Australia except northern Queensland and north-western Western Australia[8] and is one of Australia's most abundant dragonflies.[9] It is considered a dry-country dragon fly, often inhabiting the arid Australian inland.[14] The adults are vagrants[8] and highly opportunistic users of habitat for breeding.[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 nymph are able to tolerate the high temperatures found in temporary shallow ponds.[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.[9] They are also able to overwinter in cold permanent refuges,[9] and have been observed in water with a salinity between 7.8g/L to 13.9g/L.[16]

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.[14][4] Larval habitat is typically leaf litter and weeds.[9] Many aquatic invertebrates with terrestrial adult stages require a snag extending above the water surface for emergence to the adult stage.[17]

Predators primarily include fish[9] and birds.[18]

Conservation status

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.[19] Population trend is classified as unknown and no conservation actions are recommended.

References

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  1. ↑ Dow, R.A. (2017). "IUCN Red List of Threatened Species: Hemicordulia tau". IUCN Red List of Threatened Species. Retrieved 2021-06-16.
  2. 1 2 Selys-Longchamps, Edmond (1871). "Synopsis des Cordulines". Bulletin de la Classe des Science, Académie Royale de Belgique. 2 (in French). 31: 256 – via Biodiversity Heritage Library.
  3. ↑ "Species Hemicordulia tau (Selys, 1871)". Australian Faunal Directory. Australian Biological Resources Study. 2012. Retrieved 28 January 2017.
  4. 1 2 3 Watson, J.A.L.; Theischinger, G.; Abbey, H.M. (1991). The Australian Dragonflies: A Guide to the Identification, Distributions and Habitats of Australian Odonata. Melbourne: CSIRO. ISBN 0643051368.
  5. ↑ "Tau Emerald Dragonfly - Hemicordulia tau". www.brisbaneinsects.com. Retrieved 2021-06-17.
  6. ↑ Devi, M.; Indirakumar, K. (2020). "Why Insects are Dominance in the Biosphere?". Biotica Research Today. 2 (11): 1174–1178. ISSN 2582-6654.
  7. ↑ Theischinger, G., Endersby, I. (2009). Identification guide to the Australian Odonata. Dept. of Environment, Climate Change and Water. ISBN 978-1-74232-475-3. OCLC 535321248.{{cite book}}: CS1 maint: multiple names: authors list (link)
  8. 1 2 3 4 5 Günther Theischinger and John Hawking (2006). The Complete Field Guide To Dragonflies Of Australia. Collingwood, Victoria: CSIRO Publishing. p. 249.
  9. 1 2 3 4 5 6 7 8 9 10 11 Faragher, R. A. (1980). "Life Cycle of Hemicordulia Tau Selys (odonata: Corduliidae) in Lake Eucumbene, N.S.W., with Notes on Predation on It by Two Trout Species". Australian Journal of Entomology. 19 (4): 269–276. doi:10.1111/j.1440-6055.1980.tb00985.x. ISSN 1440-6055.
  10. ↑ Zielinski, Sarah. "14 Fun Facts About Dragonflies". Smithsonian Magazine. Retrieved 2021-06-14.
  11. 1 2 Yang, E.C.; Osorio, D. (1996). "Spectral responses and chromatic processing in the dragonfly lamina". Journal of Comparative Physiology A. 178 (4). doi:10.1007/BF00190184. ISSN 0340-7594. S2CID 24838606.
  12. ↑ "Odonata | What Bug Is That?". anic.ento.csiro.au. Retrieved 2021-06-17.
  13. ↑ Theischinger, G. (2006). The complete field guide to dragonflies of Australia. John Hawking. Collingwood, Vic. ISBN 978-1-4863-1375-4. OCLC 1252724816.{{cite book}}: CS1 maint: location missing publisher (link)
  14. 1 2 Watson, J.A.L. (1982). "Dragonflies in the Australian environment: taxonomy, biology and conservation". Advances in Odonatology. 1 (1): 293–302. ISSN 0168-0161.
  15. ↑ Hodgkin, E. P.; Watson, J.A.L. (1958). "Breeding of Dragonflies in Temporary Waters". Nature. 181 (4614): 1015–1016. Bibcode:1958Natur.181.1015H. doi:10.1038/1811015b0. ISSN 1476-4687. S2CID 4272949.
  16. ↑ Rutherford, J.C.; Kefford, B.J. (2005). "Effects of salinity on stream ecosystems: improving models for macroinvertebrates". CSIRO Land and Water Technical Report. doi:10.4225/08/58597507b8552. Retrieved 2021-06-14.{{cite journal}}: CS1 maint: date and year (link)
  17. ↑ Davies, Peter (1998). "Large woody debris are important habitat in rivers" (PDF). Western Wildlife. 2: 14–15 – via Wetland Research.
  18. ↑ Lenz, Michael (2018). "Mass Emergence of Dragonflies Attract Large Numbers of White-Faced Herons" (PDF). Canberra Bird Notes. 43: 290–293 – via Canberra Ornithologists Group.
  19. ↑ Dow, R.A. (2017). "IUCN Red List of Threatened Species: Hemicordulia tau". IUCN Red List of Threatened Species. Retrieved 2021-06-16.
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