Science can measure the brain's olfactory lobe and count the smell receptor cells in there, but it still can't qualify a smell in the lab -- only the nose knows whether a scent attracts or repels, and reveals this perception by words or behavior. This makes it difficult, if not impossible, to identify an absolute best smeller.
According to the number of scent receptors, the bear has the best sense of smell of all terrestrial mammals. Black bears have been observed to travel 18 miles in a straight line to a food source, while grizzlies can find an elk carcass when it's underwater and polar bears can smell a seal through 3 feet of ice. It's not all about food, though -- male polar bears have been known to trek a hundred miles following the scent of a sexually receptive sow.
Since the great white shark (Carcharadon carcharias, a.k.a. "Jaws") reportedly has the largest olfactory bulb of all sharks, it should follow that it has the best sense of smell among sharks. However, recent research at Florida Atlantic University indicates that great whites can't smell any better than other sharks, and sharks in general can't smell any better than other fish -- but add in the shark's other senses of movement in water and electromagnetics, and it still may not be safe to go in the water.
Some animals have an extremely selective sense of smell and surpass others in the detection of a particular odor. Elephants, both African and Asian, have a superior sense of smell when it comes to water, and particularly to underground water. They can scent water as far as 12 miles away, and they can remember where they have previously found water. A herd will use feet and tusks to dig waterholes for themselves to drink and bathe, but they're willing to share, so the exposed water benefits other animals as well.
Experts differ on the sensitivity of some birds' sense of smell, such as the carrion-eating condors, but New Zealand's kiwi is accepted as having an unusually keen nose for a bird. They have developed this olfactory talent because they are flightless and must find their dinner of insects and worms on the ground. The placement of the kiwi's nostrils in the tip of its bill is an unusual adaptation that makes finding food easier.
Snakes have a highly developed sense of smell, but they don't use their noses for this. Instead, they "taste the air" with their tongues, using the damp surface to catch scent particles and carry them to a special organ in the mouth called Jacobson's organ, where they can be identified as food or danger. Many other animals have a similar organ, including bears.
The champion smeller of the insect world is the male silkmoth. He can scent his ladylove as far away as 6 miles or more, and he can detect as few as one or two of her pheromone scent particles at that distance. His ardor shows itself in his walk, which becomes a stagger, as if he were drunk on love. His powerful sense of smell has inspired scientists to begin developing an artificial brain based on it that may someday become the mover of scent-detecting robots to use against drug smuggling and chemical weapons.
- Brain Facts.org: Taste and Smell
- Rhinology: Olfaction in Rhinology – Methods of Assessing the Sense of Smell*
- Prolune: The Flair of Research
- The American Bear Association: Senses of the Black Bear
- SeaWorld: Polar Bear
- Smithsonian: Ocean Portal: Great White Shark
- Fox News.com: Shark's Incredible Sense of Smell? Myth Found Fishy
- Famous Questions Script: How Many Drops of Water Are In an Olympic Sized Swimming Pool?
- Science Informer: Elephants
- St. Louis Zoo: Asian Elephant
- International Fund for Elephant Welfare: Elephants Never Forget
- Science Daily: Birds Have a Good Sense of Smell
- Smithsonian National Zoological Park: Your Kiwi Questions Answered
- Animal Planet: Reptile Guide: Snake Anatomy & Physiology
- Reptile Expert: Snake Sensory Perception
- Neuroscience for Kids: Amazing Animal Senses
- Institute of Physics: Insect Drives Robot to Track Down Smells
- BBC Future: How Silkmoths Could Defeat Terrorism and Drug Smuggling
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