Insects of a native grassland

Insects of a native grassland

We ventured a short drive north this week, exchanging our usual forest environment for an open, grassy woodland and rocky creek. On a hot Summer's afternoon we were treated to a photographic feast of insects.

The conservation value of this small patch of Lowland Grassy Woodland was recognised some 20 years ago and has been carefully managed since. A regular, planned fire regime maintains the plant community of native grasses and forbs that makes this site special. 

But I was distracted from the plants by the plethora of insects - particularly the dragonflies! They no doubt gather at this site to take advantage of the abundant prey insects. And the river and its tributary creeks are habitat for their larvae.

Throughout this post, simply click on any image to view.

DRAGONFLIES

1. Common Archtail

We had barely begun the walk and were crossing a small creek when we made our first exciting discovery. An extraordinary yellow and black dragonfly with the most amazing green eyes. And not one insect ... there were at least six, flitting about from perch to perch just above the water surface.

Eyes like this are what make dragonflies the darling of insect photographers worldwide. That, and the fact that many dragonflies will sit obligingly still for a photograph!

Plus, when it comes to species identification, dragonflies are much easier than most other insects - particularly bees! There are fewer of them, for a start. Australia has just 324 Odonata species across 30 family groups. And based on their reported distributions, there are no more than 100 species that we could expect to see in our part of NSW. 

This green-eyed dragonfly was so different to anything we'd seen before, it was clearly a new one for our insect list. Back home, with photos in hand, I set out to identify the species*.

The distinctive, arched shape of the abdomen narrows the field, and the particular pattern of yellow patches along the swollen end of the 'tail' confirms it - Nannophlebia risi, the Common Archtail. Their eggs are laid in gravelly rivers and streams.

2. Scarlet Percher

Among some dragonflies, such as the Common Archtail, there is no real difference in the body colour between males and females. In many species, however, the sexes are quite distinct.

Along the grassy tracks we saw numerous yellow dragonflies like the ones above. It wasn't until we reached the creek that we saw any red males. The common name of Scarlet Percher is apt - the red is quite brilliant. The males were clearly holding territories, flying short sorties and battles with other dragonflies and then returning to particular roosts. I assume each male was waiting for receptive females to visit his stretch of creek to deposit her eggs. 

A closer look at the photos showed that some of the yellow dragonflies we saw away from the creek were not females at all. They were immature males. 

The telling differences include: yellow at the wing base, not wing tip; the secondary genitalia beneath abdominal segments 2-3; and the shape of the primary genitalia at the tip of the abdomen ... but you have to look quite closely to pick that difference.

3. Yellow-striped Hunter

Another new species for our list! Austrogomphus guerini. And actually the first time we've seen any species from this family (Gomphidae).

The genus Austrogomphus is endemic to Australia. Of the 15 species, there are just four that we might see in this region. None of the others have a yellow dorsal stripe running along the length of abdomen. The widely spaced eyes are characteristic of the family. There is little obvious difference between the sexes. 

We saw Austrogomphus guerini throughout the reserve, including one territorial male at the creek, waging a continual boundary dispute with a Blue Skimmer (the pair in the images below).

DAMSELFLIES

The most numerous dragonfly species at the creek was actually a damselfly. The term 'dragonfly' can be used to refer to all Odonata species, or to just the 18 families of the sub-order of 'proper dragonflies', (Epiproctophora/Anisoptera). The other sub-order, Zygoptera, contains the 12 families of damselflies.

Damselflies tend to be smaller and more delicate (but not always), have equal-sized fore and hind wings, and tend to fold their wings at rest (but again, not always).

4. Common Bluetail

This is another species with a marked sex difference. In fact, most of the damselfly species we see have brightly coloured males and rather drab females. 

This female is strongly 'pruinose'. That is, she has developed a very heavy waxy coating over her body which is masking her underlying colour. It often tends to make the insect look bluish. Such waxiness is common among damselflies in the families Lestidae and Coenagrionidae, and among male dragonflies of the family Libellulidae (such as the Blue Skimmer, shown earlier).

5. Aurora Bluetail

Another Bluetail, but this one is more rarely seen. I presume it is less common, but perhaps part of the reason for the rarity of sightings is simply its size. Ischnura aurora is a truly tiny damselfly. 

I spotted this beautiful male moving amongst the grasses at the edge of the creek. Each time he flew off I struggled to keep an eye on where he went ... if I didn't see him land I really had no chance of spotting him hidden away in the vegetation. I only saw one, and no females. Perhaps they were there, but their drab colours ensured they remained hidden from view.

OTHER INSECTS

The following images do not do justice to the number and diversity of insects that we saw during our short wander about the reserve. A confession ... I was a bit fixated on the Odonata, and simply promised to return another day to spend more time watching the myriad of other insects. Most of these images are Paul's - at least one of us was open-minded in their choice of subjects!


 1. More information about Bemboka River Reserve . Special thanks to Jackie Miles for joining us on the walk, and for providing an informal guided tour as well.

2. This field guide is always my first port-of-call for dragonflies and damselflies.
Theischinger, G. & Hawking, J. 2006. The Complete Field Guide to Dragonflies of Australia. Reprinted with corrections in 2012. CSIRO Publishing, Collingwood.