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| Barry Kenway with 'Annette' (a net!) |
It has taken
some time for the club to capture the ever-busy Rod for this presentation. He
and Barry, Rob Ashdown and Chris Burwell spent many hours together catching and
studying dragonflies locally.
In 2012,
when I was speaker convenor, Barry approached me and said that he would like to
do a talk. I asked him about the subject and he replied, "Dragonflies of
course!” I thought it only one of several possible replies. Those of us who had
spent any time with Barry on walks or outings will recall that his range of
interests was well beyond dragonflies. Frogs was what I first knew him for, but
spiders and butterflies were well up the list, and it would be true to say that
every creature and plant, and their connections to the environment were his
interests.
Unfortunately, Barry passed away in early 2013,
with his talk still in the planning, but his enthusiasm was now shared with us
by Rod.
Dragonflies belong to the insect order
Odonata (meaning 'tooth jaw') which includes dragonflies (Epiprocta) and damselflies (Zygoptera). There are 29 families and 320
known species in Australia. The Order can be traced back to the Upper
Carboniferous and Upper Permian, and the two groups diverged about 230 million years ago.
The largest insect known from the fossil record is a dragonfly-like insect (Meganeuropsis
permiana of the Order Protodonata) with a 70-centimetre wingspan. This insect would be
clearly recognisable as a dragon-fly today.
All Odonata are hemimetabolous, meaning
that they undergo incomplete metamorphosis i.e. egg hatches to a nymph (known
as a naiad) which grows and emerges as an adult at its last ecdysis (skin
shedding) i.e. there is no pupal stage as seen between caterpillar and
butterfly.
All Odonata are formidable predators at
both stages of their life cycle.
The nymphs
are aquatic and are ambush predators, capturing prey (including other insect larvae,
small fish or tadpoles) by means of the labium, an elongated
extensible and retractable lower jaw structure armed with hooks. They breathe
via gills. Damselfly naiads have three leaf-like gills protruding
from their rear, while those of dragonflies have gills inside the rectum,
where water is pumped around by muscles, and oxygen absorbed into the
respiratory system.
Mature
larvae emerge from the water, cling to vegetation and shed their skin to emerge
as winged adults. Some species remain as naiads for up to two years, shedding
their skin up to 15 times.
Adults,
especially dragonflies, are swift and powerful fliers and hunt on the wing,
capturing any suitably sized flying prey, including other Odonata. The aptly
named northern American 'Dragon Hunter' has even been photographed eating a
Ruby-throated Hummingbird!
The thorax
is large to accommodate powerful muscles; the wings are strong and superbly co-ordinated.
Each of the four wings has a thickened dark patch near the tip at the leading
edge; this is termed a pterostigma, and is often found on the wings of fast
flying predatory insects. It assists with stabilising the wings at high speeds,
and during gliding.
The compound
eyes are extremely large and have up to 30,000 facets, and vision is 360
degrees in most species. There are three simple eyes between the two compound
eyes. Prey is captured and encased by spiny legs and crushed by powerful
mandibles.
Mating and
reproduction in odonata are distinctive to say the least. The male grasps the
female behind the head with a pair of claspers at the end of his abdomen. (He
is usually more brightly coloured and patterned than the female). He has
previously transferred sperm to a specialised organ just behind his thorax, and
the female now bends the tip of her abdomen forward to connect with this. This
contortion results in the of the pair making a heart outline shape. When
copulation is complete the female frees her abdomen from the male's, and they
take off with the female carried behind. The male then dips down repeatedly to
water and the female lays one egg at a time in the water or attached to
submerged vegetation.
Males are territorial and will drive off
competitors.
There are many photographs and videos of
this online for those interested.
Dragonflies
and damselflies are harmless to humans. They are not poisonous or venomous, do
not sting or cause damage or disease, but are rather considered as important
environmental indicators. They are sensitive to pollutants and poisons, and to
changes in the habitat such as siltation or water loss. They consume large
numbers of larvae and adults of mosquitoes and other biting insects.
They have
been important to Japanese and Chinese art, and were popular in the Art Nouveau
Movement. In Japanese culture they represent autumn and summer, and symbolise
power, agility and victory. Japan was once termed Akitsushima (Dragonfly's
Island) due to the large numbers flying over paddy fields (and the symbolic
connection with the importance of rice in the Japanese culture).
I will not attempt to list all the species shown in Rod's well-illustrated
presentation, but their common names are whimsical and worth listing....Scarlet
Percher, Blue Skimmer, Australian Emperor, Gold-fronted River-damsel, Unicorn
Darner, Jade Hunter, Royal Tigertail, Graphic Flutterer, Sapphire Rockmaster,
Elegant Wire-tail, Wide-faced Forest Darner, Mosquitohawk, Evening Darner,
Southern Vicetail, Pygmy Percher, Water Prince, Short-tailed Duskdarter, Common
Flatwing, Variable Tigertail, Slender Skimmer
- should be made into a song or poem.
Special
mention is due to The Australian Southern Giant Darner which achieves speeds of
50km/h; the migra-tory Wandering Glider (also aptly called Globe Skimmer), the
most common dragonfly on earth, which migrates between India and Africa flying over
the Himalayas at over 6000 metres altitude, and occurring in Australia, the
Americas and southern Europe. Some of the rarest – the Superb Emerald, and the
Thylacine Darner – are threaten by habitat loss in coastal Queensland.
Then lastly,
said to be Barry's favourite...a damselfly, the Southern Whitetip Episynlestes
albicauda.
Thanks
to Rod for a fine tribute to his and our friend Barry, and acknowledgement to
Rod, Robert Ashdown, Chris Burwell and the late Barry Kenway for photographs
used in this presentation.
(Report by Cheryl Haxen)
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