Stereo Smelling and Comparison Shopping
Scent Signposts
I trailed after my dog through the woods today. As always, I find observing his behaviour potentially educational. Towards the end of the walk, he came across a scent. He tracked it for a few yards to one side before rapidly turning and hurrying in the opposite direction, nose on the ground. Crashing and yelping came from deep in the bushes. Five minutes went by before he returned.
Obviously, he’d found a fox or a deer or something else to chase. But when he trotted into view, up on his toes, looking very pleased with himself, I began to wonder: how did he work out which way the prey went? Left or right? I use signposts when I come to a ‘T’ junction. What did he do?
It turns out that animals use a small variety of methods to follow scent trails towards a mate or food or just their way home. Scientists refer to such trails as ‘scent plumes’. The problem animals face is that such plumes don’t remain still. Think of cigarette smoke. It begins going straight upwards, then it oscillates and finally tumbles around in a chaotic manner. How can animals make directional sense of this?
It's not reliable to follow the strongest trace of scent – the wind might have concentrated a smell away from its source.
Male moths use ‘anemotaxis’. They assume the female is upwind, so follow the pheromones in that direction. If the trail breaks, they cast around until they find it again.
Land-bound insects use ‘tropotaxis’ or ’smelling in stereo’. They turn towards whichever antenna gets the strongest signal.
Mammals with narrowly-spaced nostrils (like my dog) take a comparison-shopping approach, named ‘klinotaxis’. They turn their head one way and then the other, sampling the air to decide the source of the strongest scent.
The learned article I found on Google then waxes lyrical about how scientists are building robots to mimic and beat this behaviour. Surely there are more worthy quests deserving of our tax dollars and pounds?
Fortunately, my own need for tracking does not depend upon plumes of scent or any kind of ‘taxi’. I just follow the glistening trail of slime. I don’t mind finding a dead-end crevice and having to reverse towards the target gastropod before deploying my repurposed picnic fork to guide it into my plastic bottle.
The radio this morning joined in my moaning about this season’s glut of slugs. But my ears perked up when some expert said there are many species of slug in the UK, some of which are carnivorous. Which means they eat other slugs.
Have I been killing them too? Damn!
It’s time for a quick reminder: Book 4 in my Al Sharika series is published today. You can find it on Amazon https://www.amazon.co.uk/Saved-Colonel-Book-Al-Sharika-ebook/dp/B0D52ZRTWK/ in the UK and https://www.amazon.com/Saved-Colonel-Book-Al-Sharika-ebook/dp/B0D52ZRTWK/ in the USA. Those links will take you to the three earlier books too if you want to find out how Patrick Field’s story started!
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