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You are not alone

September 11, 2018

I have recently purchased a new LED head torch which is so bright I reckon it could scorch the fur off a koala at 1000 paces. Walking at night I can now locate arboreal mammals at a great distance by their reflective eye-shine.

In the eyeball there are structures that detect light called photoreceptors. In some animals there is a reflective layer situated behind these photoreceptors called a tapetum lucidum. Once light has passed through the receptors, this layer reflects the light back through the receptors therefore making ‘double use’ of the available light. This is particularly useful for nocturnal animals to make the best use of the low light levels. This reflected light gives rise to what is commonly known as ‘eye-shine’, light reflected from animal eyes at night.

When spotlighting at night, particularly with a head torch, the location of arboreal mammals high up in trees can easily be detected by the eye-shine. I have found that frogs can also be found by their eye-shine (though it is much smaller). After a recent rain shower Pobblebonk frogs (Limnodynastes dumerilii ) on the driveway (pictured above right) or tree frogs floating in the dam (pictured left) could be easily located. In fact sitting on the edge of the dam I could see pinpoints of reflected light throughout the reeds, even though the frogs were quiet in my presence.

But what stunned me the most walking back to the house was the hundreds of reflected points of light as I passed by the cutting on the drive. Closer examination showed that the rock wall was riddled with tiny holes not obvious during the day. Sitting in these holes were Wolf Spiders (family Lycosidae). I don’t know if their eye-shine is from the same mechanism but once I got my eye in these spiders were everywhere on the ground through the bush, even floating on the surface of the dam.

So get a head torch and look for yourself. If you see nothing it does not mean that there is nothing there. They just may not be looking at you.

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