The Nose That Sniffs Underwater
Unraveling the Mystery of the Russian Desman
How a small, ancient mammal defies biological limitations with an ingenious bubble-sniffing technique
Introduction
Imagine trying to smell a flower while holding your breath underwater. It seems impossible—until you meet the Russian desman. For centuries, biologists believed that mammals couldn't smell beneath the water's surface. How could they? Olfaction, we thought, required air to carry scent molecules to olfactory receptors. But nature, as always, had surprises in store. This odd, ancient creature that looks like a star-nosed mole with attitude has been breaking the rules of sensory biology right under our noses.
The discovery that some mammals can actually smell underwater came not from the desman initially, but from its distant cousin, the star-nosed mole. Kenneth Catania, a biologist at Vanderbilt University, made the initial breakthrough when he noticed something peculiar: swimming moles were blowing bubbles while foraging underwater 8 . This observation would challenge long-standing assumptions about sensory limitations and open new doors to understanding how mammals perceive their world. The Russian desman, it turns out, shares this extraordinary capability, using a sophisticated biological system that functions like underwater sonar for scents.
The Aquatic Sniffer: Meet the Russian Desman
A Living Fossil with a Superpower
The Russian desman (Desmana moschata) is often described as a living fossil, a creature that has changed little over millions of years while maintaining unique adaptations from a distant evolutionary past. About the size of a large rat, this semiaquatic mammal sports a remarkable double-layered fur coat, webbed feet perfect for propulsion, and most notably—a bizarre, flexible snout that serves as both snorkel and sophisticated sensory apparatus 6 .
For this unusual creature, the ability to detect scents underwater isn't just a curiosity—it's a matter of survival. Desmans inhabit muddy ponds and slow-moving streams across parts of Russia and Ukraine, environments where visibility is often near zero. In these turbid waters, vision becomes virtually useless, leaving chemical senses as the primary means of locating prey, navigating territory, and avoiding predators.
The desman's habitat: murky waters where visibility is limited, making olfaction essential for survival.
Not Alone in the Underwater Sniffing Club
While the Russian desman's capabilities are extraordinary, it's not the only mammal with this talent. Research has revealed that several small semiaquatic mammals have developed similar mechanisms:
| Mammal | Habitat | Sniffing Mechanism | Primary Use |
|---|---|---|---|
| Russian desman | Murky ponds, slow rivers | Rapid bubble exhalation/inhalation | Locating prey in zero visibility |
| Star-nosed mole | Wetlands, marshes | High-frequency bubble blowing | Tracking scent trails underwater |
| Water shrew | Streams, riverbanks | Similar bubble technique | Foraging for aquatic insects |
The star-nosed mole, despite having a spectacular star-shaped nose packed with tactile sensors, still relies heavily on its bubble-sniffing ability. When researchers tested this capacity by creating underwater scent trails, moles successfully followed them with 75-100% accuracy, even when prevented from touching the trail with their sensitive noses 8 . This demonstrated that olfaction alone provided sufficient information for successful navigation.
How to Smell Underwater: The Science of Bubble Sniffing
The Mechanical Miracle of Underwater Olfaction
The Russian desman's technique is both ingenious and deceptively simple. When approaching a potential food source or investigating an object, the desman performs what researchers call "underwater sniffing"—a rapid series of exhalations and inhalations while submerged. Through high-speed videography, scientists have observed that these mammals blow bubbles out of their nostrils that make contact with objects or scent sources, then quickly suck the same bubbles back in 8 .
This process occurs at an astonishing rate—between five and ten times per second—which is comparable to the sniffing behavior of land mammals like rats and mice. The critical difference is that the desman is performing this action entirely underwater, creating a temporary "air bridge" that carries dissolved scent molecules from the aquatic environment back to its olfactory receptors.
From Water to Nose: The Chemical Translation
But how do scent molecules that are dissolved in water transfer into air bubbles? The answer lies in basic chemistry. As Kenneth Catania explained from his research on similar mammals, "Because the olfactory nerves in the nose are covered with mucous, odorant molecules are all water soluble" 8 . When the air bubbles make contact with a scent-laden surface or pass through water containing odor molecules, these compounds readily mix with the air in the bubble.
The process works as follows:
| Step | Action | Function |
|---|---|---|
| 1 | Desman exhales air bubbles through nostrils | Creates air-to-water interface for scent transfer |
| 2 | Bubbles contact object or scent trail | Odor molecules transfer from water to air bubble |
| 3 | Desman rapidly inhales the same bubbles | Returns scent-laden air to olfactory epithelium |
| 4 | Brain processes olfactory information | Identifies food, predators, or navigation cues |
This mechanism allows the desman to effectively "smell" underwater by temporarily bringing the aquatic scent world into an air-based olfactory system that evolution had already perfected for terrestrial life.
The Experiment: Proving the Impossible
Designing the Ultimate Scent Test
The initial observation of bubble-blowing was compelling, but the scientific community required more rigorous evidence. Researchers needed to demonstrate that these mammals weren't just blowing bubbles, but were actually gathering and processing meaningful olfactory information. The challenge was particularly acute for star-nosed moles, which have extraordinarily sensitive tactile organs on their snouts that could potentially provide the same information through touch 8 .
To address this, scientists devised clever experiments that separated the sense of smell from touch. They created underwater scent trails using pieces of earthworm and small fish—favorite mole snacks—then placed a fine grid between the moles and the trails. The grid openings were large enough to allow air bubbles to pass through but too small for the moles' sensitive star appendages to make physical contact 8 .
Experimental setup used to test underwater olfaction capabilities.
Remarkable Results and Implications
The findings were unequivocal. When the bubbles could pass through the grid, the moles successfully followed the scent trails with impressive accuracy. In tests with earthworm scent trails, five different moles achieved 75-100% accuracy in tracking the path to its reward. Similarly, in fish-scented trails, two tested moles scored 85% and 100% accuracy 8 .
The critical control condition confirmed the results: when researchers replaced the grid with one containing openings too small for bubbles to pass through, the moles' performance dropped to chance levels. They could no longer find the reward, despite their tactile star being equally unable to contact the trail in both conditions.
| Experimental Condition | Number of Animals Tested | Accuracy in Following Trail | Significance |
|---|---|---|---|
| Earthworm scent with permeable grid | 5 moles | 75-100% | Proves olfaction alone sufficient |
| Fish scent with permeable grid | 2 moles | 85-100% | Confirms ability with different scents |
| Scent trail with impermeable grid | Multiple moles | Chance level (no better than random) | Eliminates tactile explanation |
| No-scent control trails | Multiple moles | Chance level | Confirms scent is the cue |
Accuracy of moles following earthworm scent trails
Frequency of bubble exhalation/inhalation cycles
Performance when bubbles couldn't pass through grid
These experiments provided the first rigorous evidence that mammals could indeed smell underwater, opening new avenues of research into the sensory worlds of semiaquatic animals and challenging fundamental assumptions about olfactory limitations.
The Scientist's Toolkit: Essential Equipment for Studying Underwater Olfaction
Research into the Russian desman's extraordinary sensory abilities requires specialized equipment and methodologies. Scientists in this field rely on a combination of high-tech imaging equipment, specialized testing environments, and methodological creativity to unravel the mysteries of underwater smelling.
High-speed video cameras
Capture rapid bubble movements to document the frequency and pattern of bubble exhalation/inhalation cycles.
Glass-bottomed aquariums
Provide underwater viewing angles for observing precise interactions between bubbles and objects.
Scent trail apparatus
Create controlled odor pathways to test animals' ability to follow specific scents underwater.
Various grid barriers
Separate tactile from olfactory sensing to isolate the role of smell from other senses.
This combination of observational technology and experimental design allows researchers to overcome the significant challenge of studying sensory perception in animals that operate in two dramatically different environments—aquatic and terrestrial.
Beyond the Desman: Evolutionary Implications
Redefining Chemical Senses
The Russian desman's abilities force us to reconsider fundamental categories in sensory biology. The traditional distinction between smell (distance chemoreception) and taste (contact chemoreception) becomes blurred in aquatic environments. As one research paper noted, "Exactly the same volatile molecules, almost insoluble in water, would be considered at the same time as being smelled on land, and tasted by contact at sea" 3 .
This insight challenges the narrative that the transition from aquatic to terrestrial life required a dramatic shift in chemosensory systems, from detecting water-soluble molecules to airborne ones. Instead, it suggests that the same volatile, hydrophobic molecules that terrestrial animals smell have always played important roles in aquatic communication, just through different mechanisms 3 .
The desman represents an evolutionary middle ground between aquatic and terrestrial mammals.
An Evolutionary Bridge
The desman and other bubble-sniffing mammals may represent an evolutionary middle ground—creatures that maintained terrestrial olfactory systems while adapting to aquatic environments, rather than abandoning them as whales and dolphins did. Their solution is elegant: rather than evolving completely new sensory apparatuses, they developed a simple behavioral adaptation that allows their existing olfactory systems to function in water.
This evolutionary perspective helps explain why certain marine organisms produce volatile terpenoids—the same compounds that give many plants their distinctive smells on land. These compounds, previously thought to be useless for distance communication in water, may indeed serve important ecological functions through mechanisms similar to the desman's bubble-sniffing 3 .
Aquatic Ancestors
Early vertebrates relied on water-soluble chemical signals for communication and navigation.
Terrestrial Transition
As animals moved to land, they evolved olfactory systems for airborne scent detection.
Semi-Aquatic Adaptation
Mammals like the desman developed bubble-sniffing to use terrestrial olfactory systems underwater.
Full Aquatic Specialization
Marine mammals like dolphins largely abandoned olfaction for other senses like echolocation.
Conclusion: The Future of Underwater Olfaction Research
The discovery of underwater olfaction in the Russian desman and other mammals represents more than just a fascinating biological curiosity—it challenges our fundamental understanding of sensory perception across environments. As Kenneth Catania wondered after his initial discoveries, we might ask what other semiaquatic animals possess similar capabilities. "Do animals like otters and seals do anything similar? Or is there a size limit and it only works for smaller mammals?" 8 .
The implications extend beyond basic biology. Understanding how mammals can adapt existing sensory systems to new environments may inspire innovations in underwater robotics or scent-detection technology. Furthermore, as we face growing environmental challenges, comprehending the full sensory experience of aquatic mammals becomes increasingly important for conservation efforts.
The Russian desman, with its ancient lineage and extraordinary nose, serves as a powerful reminder that nature's solutions are often more creative than our scientific assumptions. What seems impossible—like smelling underwater—may simply require looking at the problem through a different medium, or in this case, through a carefully blown bubble.