Acknowledgments

The following people must be thanked for their contributions to this key.  Ben Gunn (CSIRO Entomology), for his contribution of taxa and character images.  Gunther Theischinger (NSW Environmental Protection Authority), for the loan of many of the specimens that were used for photography.  Richard Rowe (James Cook University) for providing a specimen of Calopterygidae.

General Information

Odonata (dragonflies and damselflies) occur in all types of inland water except saline lakes.  The adults are winged and can be found near their breeding sites or else (in some species) far from water.  The larvae, with one or two exceptions, are fully aquatic.  The larval stage lasts from a few weeks to several years, depending on species.  All Odonata are predatory in all life stages.

Species numbers usually are greatest where there is a variety of larval habitat.  A mosaic of stones, mud, and sand with a complex emergent vegetation yields the greatest range.  Some families occur across a wide range of larval habitat but others are restricted, eg to streams and torrents, to still or gently flowing water or to bogs, swamps and seepages.  Seventeen families are recorded from Australia.  One family, several subfamilies, about 60% of genera and 80% of species are endemic.

Identification

Damselfly larvae generally are similar to mayfly or stonefly larvae in overall body proportions.  Dragonfly larvae are stouter and more rounded.  Lateral abdominal gills are never present in the families known from Australia.  Identification to ordinal level is most simply achieved by looking at the underside of the head: the labium (lower lip) is developed into a large and obvious mask, hinged at its mid point and terminating in two large palps.  The mask is used as a grasping organ.  It covers  the underside and sometimes also the front of the head.  No other aquatic invertebrate has such a structure although some beetle larvae do possess a prehensile lower lip.

The two suborders, Zygoptera (damselflies) and Anisoptera (dragonflies) may be recognised from the caudal structures.  Zygopteran larvae carry three conspicuous appendages (gills) at the tip of the abdomen: one dorsal, two lateral.  Anisopterans have three small triangular projections in corresponding positions.  Unfortunately, the gills of Zygoptera are rather readily lost or damaged.  Regrown appendages often are of abnormal shape.  However, it rarely happens that all three appendages are lost in the same specimen except by rough handling post-capture.

Identification to the family level may be based on characters of the gills and mask together with other external characters.  Small specimens without partially developed wing pads (ie. specimens up to about instar 6-8, depending on species) may not be identifiable beyond the superfamily level.

References:

Allbrook, P. (1979) Tasmanian Odonata. Fauna of Tasmania Handbook No. 1. Fauna of Tasmania Committee, Tasmania, Australia.

Hawking, J.H. (1986) Dragonfly larvae of the River Murray system. Albury-Wodonga Development Corporation Technical Report No. 6., Wodonga.

Watson, J.A.L. and O’Farrell, A.F. (1991) Odonata. pp. 294-310.  In: CSIRO, Insects of Australia. Melbourne University Press, Carlton, Victoria.