Friday, 20 November 2015

A living twig

A caterpillar - or a twig
lies on a mix of fallen bark, leaves and branches
While walking through the bush a few days ago, a few kilometers from the centre of Canberra, I found this caterpillar hiding amongst some cast bark at the base of a gum tree - a Scribbly Gum. The caterpillar's camouflage was superb, and it wasn't moving, which would have given it away. But my eye was scouring the leaf and bark litter for spiders, especially peacock spiders which are magnificent if not rather tiny and very tricky to spot. But more of them in a later blog, for now follow this link to read more on them: PeacockSpider

The caterpillar is the one on the right, no the left...
The caterpillar was perched on a fallen branch lying beside fallen bark and twists of twigs which it looked just like. I think it was the distinctive caterpillar shape of a long body, hunched up and ending with two pairs of feet at the rear that attracted my eye. Then once I focused on it, of course it was obvious, yeah that would be right.

I thought it would be a moth caterpillar, and probably of the Geometridae family, and it was. It is a Fallen Bark Looper moth caterpillar Gastrophora henricaria, and it is widespread across south-east Australia. The caterpillars eat gum leaves, up in the canopy during the night, then hide in the ground litter during the day, so that all fits with what I found.

Caterpillars have six true legs as in their adult morph - and they have ten prolegs. The true legs are positioned on the thorax, as in the adults, tight behind the head. The prolegs are spread down the rest of the body and in the Geometridae  three pairs have been atrophied, leaving just two pairs close to the rear. This gap in their leg layout causes them to walk with a looping action, hence the name looper.

A looping motion as it walks and two pairs of prolegs at the very rear - a looper caterpillar
There are quite a few gum trees in the forest I was in, it is several kilometers square, so I wonder how many Fallen Bark Looper moths and their caterpillars there were in the forest - thousands, many thousands - and I only saw one. So, yes they are very well camouflaged animals indeed.

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