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5 Apr 2022

The chemistry of attraction

Written by Roddy Hamilton, ranger in the North East region
A close-up shot of a black Labrador sitting by a pond, its tongue hanging out. He looks as if he's smiling.
Your dog companion may have around 200 million scent receptors, opening up a whole new world.
We might be influenced, even driven at times, by our sense of smell, but our human response pales into insignificance when compared to that of the animal world. Ranger Roddy Hamilton puts his nose in the air and explains more.

In an early spring mini-heatwave, I found myself at the café in Crathes Castle Estate. I tell myself I followed the crowds funnelling uphill to the courtyard from the car park, but I know that’s not true. I followed my nose, quite literally, hijacked by the smell of freshly ground coffee and what smelt like lemon meringue pie. I got the coffee and realised it was not lemon meringue pie but lemon cake.

As I ate, I reflected that smell and appetite are very closely connected. I’m told that most of a good appreciation of wine comes from our sense of smell. But, above all the other senses, smell has an uncanny ability to evoke nostalgia – lemon meringue pie transports me to Christmas and the best school-dinner puddings.

I wonder if it’s like that for my dog companion. Do dogs experience nostalgia? Do they remember Christmas and lemon meringue pie? Certainly they glean much about their dog world from smell: a tree at a crossroads is marked and sniffed by so many pooches it becomes their version of Facebook.

But even a dog’s sense of smell, much admired and valued by humans, does not compare to other animals. Badgers, like dogs, have an additional cavity behind their nose with which to retain aromas for longer, so they make better informed judgments about smells. Is this food? Will this be bad for me? Walking near the Coy Burn in Crathes, my dog friend experiences a cornucopia of smells but only 100 metres away, screened from view, a roe deer is smelling even more accurately. We have 5 million scent receptors in our nose; roe deer have 250 million!

A roe deer stands in a flowery (possibly lavender) area with saplings. It has turned its head to face the camera. Its very large ears and white rump are clearly visible.
A roe deer – a scent champion!

Aroma helps humans learn about our surroundings, including other people. It’s well known that you form an opinion of someone in the first few minutes of meeting; it’s likely aroma, even when almost unnoticeable, plays a large part in influencing this. The perfume industry has latched onto this, of course; it markets perfumes with human chemicals and the claims of making you more attractive.

But it’s not just smell, either; it’s something even more powerful. If a smell can be defined as a collection of molecules that communicate something to another being, then there is another collection of molecules made in our sweat glands and the glands of animals that takes smell to a higher level: pheromones.

Quote
“Pheromones are basically smells that contain a secret ingredient – a chemical, usually a hormone – which provokes a response in another animal of the same species.”
Roddy Hamilton

This is what the perfume industry endeavours to capture – it’s the holy grail of human aroma: a scent that will make us attractive to others. The industry relies on the secretions of musk deer and a small tropical mammal called a civet to achieve this effect. As species have evolved over millennia, there are certain tricks in nature to ensure we reproduce. Scent and pheromones play a significant part in our attraction to one another – compatible people are often said to have ‘a chemistry’ – but in the world of nature, pheromones are an even more complex and intricate thing.

After I left the café, I walked down to the castle, and the scent of mahonia was heady in the air. I heard honey bees as I passed the bush. The bees were gathering nectar from the spring flowers and then would return to the colony for instructions from the queen on whether to breed, clean, or defend the nest – these instructions are delivered via pheromones.

A honey bee rests upside down on a bright yellow bead-like flower.
A honey bee collecting nectar

As we move through the summer, we can expect a bouquet of changing fragrances to excite our noses. These smells are pleasant for us but they’re absolutely crucial for attracting pollinators to the plant. I went into the walled garden, passing beneath a pergola and considered that, fine though these daytime fragrances will be, they may be outdone by their night-time counterparts. In my opinion there is nothing quite like the smell of honeysuckle and primrose on a balmy evening. It’s difficult to envisage now, but as the light fades, the scents of the garden change. The silhouettes of shrubs grow darker, until the world is navigable only by the stars and moon.

Enter the moths. And these insects, in the world of scent and pheromones, are genuinely first-place contenders. In a garden like this, the size of a football pitch, just one female moth can be found by a male, in almost pitch dark. How does it do it? With a pheromone scent. As little as one molecule of female-produced pheromone in a pocket of night air is all that’s needed for the male to detect it and fly towards it. As long as he keeps picking up the scent, he is compelled to move towards it.

A garden tiger moth rests on a green leaf with its wings spread wide. It has a brown and white mottled pattern on its upper wings, and orange lower wings with black spots.
Moths rely on pheromone communication for survival

Later, I returned to the courtyard area by the café. I noticed a spot of dropped ice-cream on the paving and an ant extricating itself from it – the first I’d seen this spring. Ants love sweet foods, which is why they are never far from us. This ant, like me, was drawn here by a scent. I left, and the ant left too. It will return to its underground nest, no doubt, delivering a message in the form of pheromones which says ‘ice-cream here’, and showering others with complex instructions to find it. We humans are far from alone in being driven by scent.

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