Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

Archives for February 4, 2008

Dead River Red Gums (Part II)

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Yesterday I posted some photographs of healthy Blue Gums in the Grose Valley.

I suggested in the comment thread that followed, that River Red Gums are more suseptible to fire, and that a fire in October 2006 in the Barmah forest destroyed many trees.

River Red Gums are also susceptible to drought.

The following photographs were taken in the Murray Valley last November.

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West of Koondrook before the Kerang turnoff, November 21, 2007

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West of Koondrook before the Kerang turnoff, November 21, 2007

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West of Koondrook before the Kerang turnoff, November 21, 2007

Trees along the Murray River were healthy, but this isolated stand of trees on a farmed section of the floodplain appeared mostly dead – I assume from drought.

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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