Petalura gigantea, wing span approximately 12cm
gigantea: an ancient bog-dweller in trouble
the early Jurassic Era, 190 million years ago, enormous dragonflies
of the anisopteran family Petaluridae lived in swamps and
bogs on the ancient continents Laurasia and Gondwana. Their fossil
remains, readily recognisable by a unique wing venation, have been
found at sites in Europe and the former USSR.
came and went, mammals radiated, birds discovered flight and plants
invented flowers. On swamps and bogs across the newly-formed continents
of America, Eurasia and Australasia the Petaluridae lived
on. Today the family is much reduced in range but essentially unchanged
in form and habit from those early times. Nine widely scattered
species survive: four in Australia, one in New Zealand, one in Chile,
two in North America and one in Japan.
Australian species two live in the rainforests of north Queensland
and one inhabits boggy seepages near Perth. But the best-known species
in the whole family, the type species, Petalura gigantea,
is found in NSW. With a wing-span of just under 140 mm, a body as
thick as a finger, and heavier than a fairy wren this brown and
yellow giant is one of our rarest dragonflies.
surviving species are threatened by human activities. P. gigantea
was recorded last century from marshes at Sydney and Cronulla but
these are gone. Today it is found on isolated swamps in the eastern
part of the State. Records plus a few unconfirmed sightings suggest
it survives in the Royal National Park, in the Blue Mountains, on
the Nightcap Range in the far north of the State and on Fraser Island
off the Queensland coast. However, the largest and probably the
most viable population is at the Wingecarribee Swamp near Moss Vale.
There it lives on untouched marsh adjacent to a peat mine. It does
not occur on open water or over the mine itself.
gigantea is a very unusual dragonfly, even apart from its great
size. Two features explain its vulnerability. First, surprisingly,
the adults are rather poor flyers and hopelessly bad at dispersing.
Emergence takes place in late October and the flight season runs
until January, but adults are never found far from their emergence
site. By night they roost in trees at the swamp edge. By day they
settle on the swamp itself where they perch on top of low vegetation
or hang vertically from a branch.
one will fly up and grab an insect to eat. Occasionally a male will
patrol across the swamp or a female will lumber in from the surrounding
area and with her short, curved ovipositor insert eggs one-by-one
deep into the mat of sphagnum and roots which covers the swamp.
Sometimes a mating pair flies together in the tandem hold; the male
in front, gripping the female by the back of her head and cloaking
her prothorax with the peculiar petal-like claspers at the tip of
his abdomen. But on the whole its a quiet life as an adult petalurid.
Within 10-20 km of Wingecarribee Swamp are several boggy seepages
and apparently suitable sites, but P. gigantea seems incapable
of finding them.
the larvae are very slow growing, very long lived and, for a dragonfly,
have very peculiar habits. Most dragonfly larvae are fully aquatic
but those of Petaluridae are semi-terrestrial. At night and in wet
weather they roam the surface of the swamp in search of insects
and other arthropods to eat.
of the time they retire to a permanent burrow, a long chambered
passage with its opening above water level but extending deep into
the swamp. Each year the burrow is made longer. The larval stage
in P. gigantea is known to last at least 10 years but estimates
based on burrow lengthening make a time-span of 20-30 years quite
likely. Most probably the time-span varies by several years, even
within a cohort.
the combination of poor dispersal ability, long larval life and
an absolute need for permanent swamp with a stable water-table which
makes P. gigantea so susceptible to human interference. Draining,
mining, flooding or infill simply destroy the larvae in their burrows
leaving no adult population to recolonise the swamp. One excellent
way to ensure that the 190 million year history does not stop right
now would be to preserve all known habitat - it wouldn't take much
effort, there isn't much to save. A State-wide search for unknown
populations would be very useful in order to better assess the situation.
very worthwhile activity, though potentially long term, would be
further study of the larval stages to identify habitat requirements
and better estimate the time from egg to adult. As with so many
of our native invertebrate animals there is much we do not know
about this unique dragonfly. We need to start finding out before
it is too late.
Trueman is a Lecturer, in the Division of Botany and Zoology, Australian
National University, Canberra.
by John Trueman, The "Giant Dragonfly", http://www.anu.edu.au/BoZo/trueman/labsite/petalura.htm,
2000 (More photos and info available at this site).
Trueman, Petalura gigantea, National Parks Journal, August