Come Hither

It’s not news to anyone that many animals, if not most, possess a far more sophisticated sense of smell than we. For us English-speakers, even the word “smell” conjures malodorous scents before it reminds us of fresh-baked bread. “You smell,” for example, is never a nice thing to hear, unless it’s qualified with “…nice,” or “…like fresh-baked bread.” Though it is the sense most associated with memory, and the larger part of our ability to taste, we tend to ignore our day-to-day scents and only appreciate them when they are new, or particularly wonderful or evil. A dog, for example, seems much less judgmental about the smells in its world, being equally appreciative of flower gardens and strangers’ butts.

But most animals, despite their superior noses, are simply highly attuned to one or a few scents. Bears have the greatest senses of smell, about seven times greater than a bloodhound’s and over 2,000 times better than a human’s, and can smell a carcass from 20 miles away, if the wind is right. But bears are generalists, so they are attuned to a wide range of things. A specialist, like a turkey vulture — the best nose in the bird world, though most birds have little to no sense of smell — can detect rotting meat from several miles away and several miles in the air, but only rotting meat. A shark can detect a single drop of blood in the water from half a mile away. A salmon can smell the particular melange of moss, roots, and soil of its native stream in the ocean at a ratio of one part per trillion. But when it comes to the scent of a woman, there is no bloodhound like a Saturniid moth.

The Saturniidae are a family better known as wild silk moths, for their silky cocoons. But their fame among lepidopterists is won for their enormous size and their breathtaking beauty. These are the largest of the moths and butterflies, making them some of the largest insects in the modern world. The Saturniids include the world’s largest moth, the Atlas Moth of South America:

He shrugs.

And the largest moth in North America, the Cecropia:

The most beautiful moth, in my opinion, the ethereal Luna Moth:

And the star of our show, the Polyphemus:

Named for Polyphemus, the giant cyclops in the Odyssey (though I keep counting two false eyespots, no matter how I squint), this king of the night wears an equally impressive crown of antennae, far larger than his queen’s. As a caterpillar, he was voracious, but now that he is an adult, he lacks both mouthparts and a digestive tract. So the feathery antennae are not to find food, but a mate. She will be resting against a tree somewhere, producing a perfume of pheromones from her abdomen, each long-stranded molecule swirling in the tiny eddies of wind created by the leaves and branches. It is siren song to a male Polyphemus. The 60,000 sensilla — the sensory hairs — on each antenna bear 150,000 receptor cells, all programmed both to recognize individual parts of a pheromone molecule and to send impulse signals to the part of his brain that controls behavior. Upon touching any part of a single molecule of her scent, the moth is irresistibly drawn to her, body and soul. He is no longer in control of himself, but commanded by a single silent word sent to him over a long dark distance, a whisper on the wind.

In fact, if you whisper the word “love,” that one exhaled syllable is a wilderness of scents to a moth. One note of air in the symphony of the night forest is excruciatingly loud: it might contain particles of pine and oak pollen, the bouquet of mildew and skunk and wild rose, fruiting mushrooms and dirty water and bobcat scat and the stink of every other desperate, lovelorn insect tonight. But the Polyphemus moth isn’t listening for these, only the chemical voice of his future beloved. He is so attuned to her come-hither scent that he can detect a single molecule of her in a cubic yard of air, picking it out of trillions of molecules like a diamond earring from the sand. He can smell her from seven miles away. If it is raining, he will fly through the rain to her. If the storm blows against him, if there are cliffs to climb, he will still sail the merciless night to find her.

He does not fly directly into the wind, instead using a fairly sophisticated technique called anemotaxis: by measuring wind speed and direction against his own movements and the increasing potency of her, he can effect a beeline for her even if she’s not directly upwind. The two antennae work like a witching rod or a snake’s tongue, and the moth zig-zags the way a bloodhound sways its head from side to side, nose buried in the criminal’s tracks. When we walk, the grass catches part of us, and so the female moth leaves her pheromone fingerprints on leaves and the surface of water, clues and hints for the male to trace. She is not here, but she touches the treetops and stoops to the closed trilliums. She is not here, but he can hear her ghost singing in the forest. Drop by drop, molecule by molecule, he struggles towards her, crashing through the undergrowth, drumming his enormous wings against the beech leaves. The great yellow owl eyes on his wings flicker, searching. There are real owls here, hungry owls listening for him in the night like stethoscopes listening for the beating of a poisoned heart. But he cannot stop. He has heard her name, found just an iota of this moth he has not met yet, and he is no longer his own. He is hers, and he will collect the drops of her one by one as he swims to her, thrashing like a killer’s mind, a beautiful delirium, the drowning man’s breaststroke. It is not his journey; it is her command. It is not his mystery to solve, but her seeking him. She beckons, as if with a crooked finger, across the treacherous river of night. He leans in over the miles, a living kiss without a mouth.

About quantumbiologist

Christian Drake, AKA The Quantum Biologist, is a naturalist and poet formerly of Albuquerque, NM and currently living deep in the backwoods of the Connecticut Berkshires. He has worked in aquariums and planetariums, national parks and urban forests. When not birding or turning over rocks to find weird bugs, he enjoys rockabilly music, gourmet cooking, playing harmonica and writing dirty haiku. View all posts by quantumbiologist

21 responses to “Come Hither

  • Sir Pilkington Smythe

    I’ve always wondered on these ‘a dog’s smell is 2,000x better than a humans’ type comments… how are they measuring it? Amount of smell receptors? What about how much of the brain is used to process the info? Always strikes me as an odd thing to say…

    • Copernicus

      At least in the case of dogs, let us not ignore the role of the Jacobson’s Organ. The jury is out as to whether we humans still even have this organ after our fetal stage, but I swear I’ve seen guys display a flehmen response in some social situations.

      This vomeronasal function takes a dog’s “smelling” into a dimension that is almost beyond what we can imagine; indeed, their pheromone detection goes to a different area of the brain than does their routine odor detection.

      • Sir Pilkington Smythe

        Yes good point, and of course there are many creatures that can ‘smell’ electricity too. Though I thought the case was pretty closed on humans using the VNO, they don’t as far as I remember… you heard anything otherwise?

      • Copernicus

        Aug 2000 ENT Journal:

        Maybe some folks have and some folks don’t.
        Gary Busey, for example, can track you from 35 miles away.

      • Copernicus

        While my links “await moderation” for some reason, let me refer you to the Aug. 2000 edition of the ENT Journal.
        J.Won et al. Respectable authors. I do note that this research, which finds cellular evidence for the system in a certain percentage of individuals, does not speak to the issue you raise, which is whether human actually use the system. I suppose one can also ask whether, in humans where the cellular equipment is found, there has to be actual awareness of the sensory input, or whether it can be subconscious.

      • quantumbiologist

        Yes, but the Flehmen response might be an evolutionary tic at this point, left over from when we did have an active Jacobson’s organ, and now only activated in response to pain, displeasure, or Elvis impressions!

    • quantumbiologist

      It’s a brain size thing. The part of your brain that recognizes scent is called the olfactory bulb. A bear’s bulb has five times the surface area of ours, even though a bear’s brain itself is one-third the size of a human noggin. Also, their noses contain hundreds of muscles, giving them roughly the same range of motion and dexterity as a human finger; a sure sign of the bear’s reliance on its nose. Factor in some anecdotal evidence about bears traveling twenty miles for some Spam, and you come to the estimate of 2,100 times the smelling power.

      As for the VNO, my conversations with the owner of the Rattlesnake Museum here in ABQ have led me to understand that it does exist in humans, but only vestigially. I understand that it’s still quite active in prosimians, though.

      • Sir Pilkington Smythe

        oooh you is bold in your statements…
        yep naturally olfaction is controlled by the olfaction bulb in the brain, or in leyman’s terms ‘the smelly bit is controlled by the smelling section of the thinky bit’.
        but if the bear’s smelling section of its brain has a surface area five times the size of ours that certainly doesn’t mean its sense of smell is 14,000 times better than our sniffer… working on the theory of a bloodhound’s being 2000 times better than a humans, and a bears being seven times better than a bloodhound (equals 14,000)
        not least because;
        a) size of brain doesn’t denote ‘betterness’, the sperm whale’s brain weighs eight times the weight of a human brain, and he’s dreadful at boggle.
        b) using surface area as a demonstration of size is misleading, for example something that is tiny; 1cm by 1cm by 1cm has a surface area of 6cm , something that is still very small; 30cm cubed has a surface area of 27000cm, something still as small as 1m cubed is 1000000000 cm surface area… so yep not a clear way of demonstrating size
        c) my tiny mind has spent so much time doing sums (45 seconds) i’ve completely forgotten about c)
        moving on;
        the bear’s nose might have as many muscles as a finger (I haven’t checked) however fascinating that is, it has little relevance to whether it can smell a smelly smell
        gah, anecdotal evidence, and what the blazes do rattlesnakes have to do with VNO in humans…
        apologies QB, I’ve had a couple of G & T’s, am not trying to be a bother!

      • quantumbiologist

        Nothing. As a non-herpetologist (hell, I studied botany primarily), I only learned about the Jacobson’s organ a few years ago at my first visit to the Rattlesnake Museum, and pressed the herp guys there as to whether or not we have the same.

        Okay, let’s break this down. The average dog’s sense of smell is 100 times greater than a human’s. A bloodhound’s is three hundred times greater than a human’s. And a bear’s sense of smell is seven times greater than a bloodhounds, for a total of 2,100 times better than ours.

        Now, not only is the bear’s nose more muscular — which indeed could be said of most animals — but it also has hundreds of times more sensory receptors than ours, as well as a highly increased surface area. The nose muscles don’t quantify its ability to smell, only point out how important the sense of smell is, as I said.

        But that surface area absolutely IS relevant, as that determines the number of neurons you can pack in there. You talk about the weight of a sperm whale’s brain, and I say, what is the surface area of it, and more importantly, what’s the brain-to-body mass ratio? The sperm whale has a bigger brain but a much lower brain-to-body mass ratio — or “encephalization quotient,” an imperfect rule of thumb for estimating intelligence, to be sure, but a generally good one. But the sperm whale has an extra lobe, making it slightly more complex than ours, and indeed it is a very intelligent animal, like most cetaceans. Just ask Ahab.

        Anyway, you most certainly can judge a bear’s ability to smell by the size and surface area of its olfactory bulb!

      • Sir Pilkington Smythe

        ok to begin with the VNO is found in a whole host of creatures
        secondly, can you add any basis to why the animals you list have a ‘better’ sense of smell… (the whole point i was making in the first place)
        why is a dogs sense of smell 100x better than a humans?
        and a bloodhounds three times better than that?
        and a bears seven times better than that?

        surface area doesn’t determine the amount of neurons you pack in, volume however does

        as for the false science of ‘encephalization quotient’ according to this calculation the most intelligent creatures on Earth would be songbirds…


        ps apologies, I’ve been drinking…


      • Copernicus

        Dogs have 220 million olfactory receptors; humans have 5 million.

        But your main point is good: passerines rule.

      • Sir Pilkington Smythe

        Apologies, I came in from my birthday and had had a few!

        Anyway to continue arguing like a drunken buffoon;

        Surface area is a deeply misleading way of representing size, something that has five times the surface area is very likely to be less than twice the size of the original object… and it is the size of a part of a brain that will ROUGHLY determine how many brain cells (neurons) are in there.

        You can make a GUESS about how well a bear smells from the volume of its olfactory bulb, anyone who used its surface area would be practising terrible logic.

        I assure you that the sperm whale’s brain is not more complex than the human brain, even if it does have an extra lobe. While sperm whale’s are undoubtedly intelligent, and even have a culture, they aren’t even capable of even the simplest household chores…

        Sorry QB but if you are making these bold statements you are going to have to back them up!

        Copernicus – so a dog has 44 times more smell receptors than a human? Still doesn’t add up to me?!


        Sir P-Sx

      • Copernicus

        So when you say that a jumping spider has ten times better vision than a dragonfly…

      • Sir Pilkington Smythe

        Very good! Touche!
        Yep I can’t remember where I got that from, wrote it well over a year ago… I’ll try and dig it out…

  • quantumbiologist

    I might add, fellas, how amused I am that one of the most interesting scientific debates in any of my posts so far follows my attempt to write porn for moths.

    • Copernicus

      I thought commenting on, y’know, Jacobson’s Organ would be kind of a segue.

      • quantumbiologist

        Indeed! And for those of you wondering what this Jacobson’s Organ/VNO we’re talking about is, cue the following clip up to the 2:00 mark. Check out the blinded snakes of Carnac Island!

      • Copernicus

        What’s fascinating to contemplate is that the “smelling” capacity of an animal with VNO (or a Jacobson’s organ) is almost a distinct perceptual sense of its own. While it still relies on the perception of airborne molecules, the neural pathways and brain processing of the information is not the same as traditional “smelling.” In a way, it seems analogous to the visual perceptual capacities of the trigger shrimp; not just an enhanced sense but a sense expanded by several orders, and processed in ways that defy prediction.

      • quantumbiologist

        Absolutely! And it’s the same with the Saturniid moths. Using hypersensitive antennae instead of a nose challenges the perception of “smell,” and the fact that the antennae interpret the pheromone themselves and relay the message directly to the behavioral part of the brain instead of the interpretive part further blurs the definition beyond any sense of “smell” we can really imagine.

  • Bert

    Very much enjoyed your article, but two nits to pick. Atlas moths range SE Asia, not South America. I’m wondering if your Cecropia image is actually a Colombia Silk Moth. Cecropias are usually red-headed and grey-winged, where as the Colombia looks just about the same but usually has a more cinnamon and also cinnamon color scheme.

    • quantumbiologist

      Whoops! You are absolutely right, on both counts. Bugs are my weak suit, and I’ve become accustomed to pulling pictures off the internet, which isn’t all that reliable sometimes. Thanks for the corrections!

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