Animals With the Best Sense of Smell

The African elephant has the largest set of smell receptor genes any species has been found to have. A 2014 study in Genome Research counted 1,948 working ones in its genome. Rats, which held the record before, have 1,000 to 1,200, dogs have about 800, and people have about 400. A gene count is not a nose test, so this page also covers what university, museum, park, and journal sources say about snakes, moths, bears, sharks, and giant pouched rats.

Which Animal Has the Best Sense of Smell?

It depends on what is measured. Counting receptor genes puts the African elephant first. The study's authors say it is unclear which part of olfactory ability that number reflects. They write that it is reasonable to assume a species with more of these genes can tell apart subtler differences between related odors, and that the count sets "the resolution of the olfactory world rather than the sensitivity to a given odor."

The authors assume a larger count lets a species tell apart subtler differences between related odors, and they say it says nothing about how faint an odor it can detect. No source on this page ranks every animal in one list, so each section below says what its source measured.

Animals With the Best Sense of Smell

Olfactory receptors detect odors in the environment, and the Genome Research paper counts the genes behind them in 13 placental mammals. The number of these genes varies greatly between species and reflects each species' lifestyle. The chart shows the counts the paper reports for four of them.

Two species with similar counts can still smell different things. The paper found that dogs and guinea pigs each had about 800 of these genes, but only about 51 percent of them were shared. Dogs have their own pages on this site, including how dogs can tell time with their noses and why dogs mark their territory. If you share your home with a dog, the dog shirt collection is one click away.

African Elephant

A study of 13 placental mammals puts the African elephant's repertoire at about 2,000 working olfactory receptor genes in its abstract and 1,948 intact ones in its full text. The paper calls that "by far the largest repertoire" of intact genes ever identified within a single species, and more than rats, which had the largest previously identified.

Behavior tests are a separate kind of evidence. In a test the paper describes, Asian elephants told apart 12 pairs of mirror-image odor molecules and 12 other odor pairs that differed by only one carbon. The authors say that shows elephants perform at least as well as mice and clearly better than humans, pigtail macaques, or squirrel monkeys in olfaction tests. They also write that no systematic studies of African elephants' smell have been published. African elephants reportedly can tell two Kenyan ethnic groups apart by smell, and can possibly recognize up to 30 family members from scent in mixtures of urine and earth.

Our post on the Great Elephant Census reports that African savannah elephant populations fell by an estimated 30 percent between 2007 and 2014. Our post on the Barnum elephants covers the end of the Bailey Circus elephant shows.

Snake

Snakes smell mostly with their tongues. Washington State University's Ask Dr. Universe explains that a snake pulls scent molecules from the air into its mouth with its tongue. The molecules then reach a part of the roof of the mouth called the Jacobson's organ, which decodes them into smells. The page adds that snakes also use their nostrils to take in odors, and that Rocky Parker, an assistant professor at James Madison University, said we are still learning exactly how snakes use their nostrils, tongues, and Jacobson's organs to smell the world.

The same page says lizards flick their tongues in different patterns to collect odors, and elk and deer lift their upper lips to move molecules into their mouths. Snakes also need their nostrils to breathe. Oxygen reaches the body through them, so the nose has a second job for breathing.

Moth

The University of Utah's page calls a moth's antenna "the nose, essentially." Odor is very important to a moth's life. The page says moths' sense of smell drives most of their behaviors, and biology professor Neil Vickers says what moths do "is predicated on odors." Male moths find females through pheromones, and females locate a place to lay eggs by following plant odors.

The university's page says each moth species develops receptors to pick up only the odorants it is interested in. In the study it reports, researchers took the cells that grow into antennae from more than 350 caterpillars of one species and transplanted them into another species. The adult moths responded to a pheromone blend that neither species makes naturally, according to the PLOS ONE paper.

Black Bear

The National Park Service's Yosemite page on black bears says the area inside a black bear's nose, called the nasal mucosa, is a hundred times greater than ours.

Great White Shark

The Smithsonian Ocean page on the great white says its most acute sense is smell. It says that if a single drop of blood were floating in 10 billion drops of water, a great white could smell it. The shark's nostrils are on the underside of its snout and lead to an organ called the olfactory bulb. The page reports that the great white has the largest olfactory bulb of any shark.

Smell is one of six senses the page lists for sharks: smell, hearing, touch, taste, sight, and electromagnetism.

African Giant Pouched Rat

Pet rats appear on our list of the best small pets for kids. The African giant pouched rat is a different rodent, and a National Geographic story on the African giant pouched rat covers its work with landmines. The Belgian nonprofit APOPO trains these rats for that job.

Researchers who used giant African pouched rats to find land mines in Mozambique chose them because they have an excellent sense of smell, weigh too little to activate mines, and are native to sub-Saharan Africa. In 2009 the rats searched 93,400 square meters of land and found 41 mines and 54 other explosive devices. People with metal detectors found no additional mines. The rats gave an average of 0.33 false alarms for every 100 square meters, which is below the threshold the International Mine Action Standards set for accrediting mine-detection animals.

Cows

It’s also said that they have a stronger olfactory sense than dogs in that they are able to differentiate scent particles from each other. This is particularly helpful when trying to avoid poisonous plants and other things which might harm them.

FAQ

How many smell receptor genes do humans have?

The Genome Research paper says the human genome holds about 400 functional olfactory receptor genes. It also says higher primates generally have much fewer of them than mice, rats, cows, and opossums.

Can pouched rats detect disease?

A review in The Behavior Analyst says giant African pouched rats have been taught to detect tuberculosis in human sputum samples. It says available data suggest the rats are sufficiently accurate in detecting TB to merit further investigation as a diagnostic tool.

Sources

• Niimura Y, Matsui A, Touhara K. "Extreme expansion of the olfactory receptor gene repertoire in African elephants and evolutionary dynamics of orthologous gene groups in 13 placental mammals." Genome Research, 2014. pubmed.ncbi.nlm.nih.gov.
• Washington State University, Ask Dr. Universe. "If snakes smell with their tongues, what do they do with their noses?" 2019. askdruniverse.wsu.edu.
• University of Utah, UNews. "What a moth's nose knows." unews.utah.edu.
• National Park Service, Yosemite National Park. "Bear Series, Part One: A Bear's Sense of Smell," 2014. nps.gov.
• Smithsonian Ocean. "Great White Shark." ocean.si.edu.
• Poling A, Weetjens B, Cox C, Beyene NW, and others. "Using trained pouched rats to detect land mines: another victory for operant conditioning." Journal of Applied Behavior Analysis, 2011. pubmed.ncbi.nlm.nih.gov.
• Poling A, Weetjens B, Cox C, Beyene NW, and others. "Tuberculosis detection by giant african pouched rats." The Behavior Analyst. pubmed.ncbi.nlm.nih.gov.
• Arew. "Are cows sensitive to smell?" arew.org.
• National Geographic. "Meet the Giant Rats That Are Sniffing out Landmines." nationalgeographic.com.
• APOPO. apopo.org.