Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

neil

Robber Flies

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Beauty, it is said, is in the eye of the beholder … so behold, the beautiful Robber Fly. These predatory insects launch into attack from an established perch and catch their prey on the wing. Strong, heavily barbed legs grasp the prey, which is lanced with modified mouthparts in the form of a stabbing proboscis, injecting saliva containing neurotoxic and proteolytic enzymes.

Robber Flies are somewhat intimidating in close proximity. Unlike March Flies, they do not seem interested in human fare, but they are invariably given wide berth, nonetheless.

I associate the presence of Robber Flies on nocturnal vegetation with the change from cold and secretive to hot and revealing.

Lichen Spiders (Part II)

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In an earlier entry, Lichen Spiders (October 18, 2007), Jennifer described the images of the spiders as intriguing and asked how difficult/expensive it would be to develop the seven images as separate posters/pictures.

I have since accumulated a collection of eight high quality poster size images (30 x 45 cm @ 240 dpi), presented in the thumbnail mosaic below. Interested inquiries should be directed to neil@ccwild.com

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As can be seen within the collection, Lichen Spiders vary in conformity with their background occupancy. However, according to the Queensland Museum Inquiry Centre:

Spider colour is fixed at its previous moult. A slight exception being the abdomen with its much thinner walls which may change especially according to accumulated waste products or what it has eaten. So they can’t change colour like a frog, gecko or squid. Some species of spiders that camouflage on tree bark have multiple colour forms however.

So far as is known, a lichen spider would not be selecting a background according to colour as these are like most (but not all) spiders in having poor vision. It is expected that they would have other ways of detecting a nice lichen-covered background to sit against however.

Under closer scrutiny, the eight images (fully magnified), reveal variation to spider appearance through differential combing of hairs, which appear to have reflective qualities. In the eighth (bottom right) image, much of the blending is also complemented through the shared occupancy of its offspring (see enlargement).

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The Giant White-tailed Rat

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One of Australia’s largest native rodents, the Giant White-tailed Rat (Uromys caudimaculatus) has such formidable teeth and jaw strength, they have been known to eat through steel garbage bins. They are also capable of dispersing large-seeded tree species in Australian tropical rain forests, including some that have no alternate vector, such as the magnificent Yellow Walnut (Beilschmiedia bancrofti) (Lauraceae).

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When I first settled into the Daintree rainforest, I was surprised by the local council’s provision of free rodenticide for “vermin control”. Never mind that these were protected species and inhabitants of World Heritage estate, apparently they were rats first and foremost and therefore vermin.

There is quite a diversity of native rodent fauna in the Daintree rainforest, but as far as I know, no introduced species. The Bush Rat (Rattus fuscipes coracius) looks most like the notorious Black Rat (Rattus rattus) of bubonic infamy, but even these are protected by legislation.

Over the years, newcomers settling into the rainforest have expressed dismay at the intrusion of rodents with not the slightest regard for the meticulously installed barriers of fly-wire mesh. Aggrieved home-owners almost invariably resort to trapping the trespassers, as sensitively as possible, and transporting them to a remote corner of the Daintree for release. Like-minded counterparts could very possibly be doing the same thing, from the opposite direction and it would be interesting to know how this shuttling of rats around the rainforest affected their social dynamics, for it most certainly does not affect the continued breaching of residential boundaries. Residents either accepted the inevitable or leave.

Weblog Cost-Recovery

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Do you see what I see? There is a new ‘Donate’ feature on the home-page of The Politics & Environment Blog. Its purpose is self-evident and it is hoped that members of our weblog community will consider availing themselves of the facility to help share the load, as it were.

Since the 14th April 2005, when the site was first launched, over 1,515 entries have been published eliciting some 41,440 comments. It has become quite the gathering place for our community of interest. Whilst we are often conflicted by ideology on issues raised, we also embrace strong environmental values, which for many would include sustainability and ‘user-pays’. It could be said that expenditure and environment often make for strange bedfellows, but the fact is, there is a growing cost to the maintenance and operation of the weblog.

In another popular gathering place, visitors to the Daintree rainforest consistently express strong expectations that the destination will reveal sightings of some of Australia’s most unique wildlife in natural habitat. Unfortunately, the majority are unsuccessful and not because the ecological values of the landscape fall short of the mark, but that the travel-style is so completely contradictory.

Three-quarters of the half-million (or so) travellers per year are bound to the travel-intensive itineraries of day-visitation out of Cairns or Port Douglas; only a quarter stay overnight. There is also a significant destination bias, with summer holidays from the northern hemisphere and escapees from the winter chill of southern states, supplying the largest numbers of overnight visitors to the winter rainforest at is most dormant.

Elusive encounters with rainforest beauties, like the (above) male Orange-thighed tree-frog (Litoroia xanthomera), are few and far between. Visitors would be well-advised to travel into the rainforest at the hottest, wettest time of the year and to engage the expertise of a local inhabitant, to maximise prospects for successful sightings. However, to do so they would need to stridently go against the flow and direct their travel dollars more purposefully.

Perhaps the same could be said of the weblog; a purposeful direction of economic support might bolster the vitality of the forum even more substantially than the rigour of free comment.

Australia’s Largest Lepidopterans

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The Bleeding Heart (Homalanthus novoguineensis) is the preferred food plant of the caterpillar (above), which attains a length of 12 cm and produces Australia’s largest moth: The Hercules (Coscinocera hercules).

The female moth has a slightly paler and larger wing area than the male (below), whose wingspan reaches up to 27 cms.

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The female Cairns Birdwing (Ornithoptera euphorion) (below) is Australia’s largest endemic butterfly species, reaching a wingspan of up to 16 cm. Males are usually a few centimeters smaller.

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The caterpillar of this species (below) prefers to feed upon the native rainforest vine Dutchman’s Pipe (Aristolochia tagala).

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More Male Crocodiles in a Warmer World?

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This dominant 4.5metre male Estuarine Crocodile (Crocodylus porosus) resides a kilometre or so downstream from my own abode on Cooper Creek; a proximity that we never forget!

It has long been known that crocodile gender is determined by temperature. If the temperature of egg incubation is cool, around 30 degrees C, the hatchlings are all female. Warmer temperatures, around 34 degrees C, hatch all males. There is also strong population bias towards females; often as high as 10 to 1.

For about thirty years, this skewed ratio was thought to provide an evolutionary advantage, whereby sex ratio optimises survivorship considerations.

In a recent News in Science article by Dani Cooper, entitled ‘Sex-change lizards settle a hot topic’, Professor Rick Shine of Sydney University and his former student Dr Daniel Warner, now of Iowa State University, report that they have proven this 30-year-old theory.

Studying the relatively short-lived Jacky dragon (Amphibolurus muricatus), which produces off-spring within one year of hatching and lives no longer than four years, the researchers found that hormonal manipulation of gender determination had no effect on the health and survival of the hatchlings, but the natural males were five to 10 times better in terms of mating and producing offspring, while the natural females produced four to five times more offspring.

It was therefore shown that the incubation temperature that produces that sex in nature optimised reproductive success of each sex.