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Can Crocodiles Smell Blood? (Crocodile Olfactory System)

Yes, crocodiles can smell blood. Their sense of smell is well developed, and they can detect prey even if the carcass is far away. 

Crocodile eating meat
Crocodiles can smell food from a distance due to their highly developed sense of smell

Crocodiles use chemoreception for hunting for food. They can smell prey on both land and water. Crocodiles, however, cannot smell while underwater because they do not breathe during a dive. They close their nostrils when underwater, so smelling is not possible. 

How does a Crocodile’s Sense of Smell Work? 

Crocodiles have only one olfactory chamber and lack the vomeronasal organ (VNO), also known as Jacobson’s organ that’s present in some other animals like dogs. Because of its absence, the crocodile’s sense of smell relies solely on the olfactory chamber. 

The VNO is present in many animals such as cats, dogs, pigs, and even primates. Some humans have remnants of it, but these are not functional. 

Many experiments prove that crocodiles can smell chemicals in the air and water. It is this keen sense of smell that they use to hunt. When above water, they detect the smell that the water and wind carry. 

When underwater. The hunting technique of the crocodile is tactile, which means it uses its scales or skin to feel the surroundings.

In a study, scientists found out that extant crocodiles have valvular nostrils and that the crocodiles control these nostrils with smooth muscles. The crocs also have flaps that close the nostrils when underwater

Dark colored alligator
Crocodiles have to keep their nostrils above water to smell

Related Article: All 27 Types of Crocodiles

Can Crocodiles Smell Underwater? 

No, crocodiles cannot smell underwater. Unlike sharks and many species of fish, crocodiles do not have gills. Crocs also do not have the same olfactory system as sharks. 

Since a crocodile can not breathe underwater, they are unable to smell underwater.

Contrary to what people say, sharks cannot smell blood underwater miles away. Sharks have similar sell sensitivity as many other fishes. They can detect smells between one part per 25 million. Some can smell one part per one billion.

Water passes through the sensory cells of the shark, just within the skin folds. The sensory cells pick up the scents. Crocodiles do not have this function. Water does not pass over sensory cells for smell because they do not breathe underwater. 

Read More: Can Crocodiles Hunt Hippos?

How do Crocodiles Hunt Underwater if they Cannot Smell? 

Crocodiles hunt underwater through the tactile sense. Crocodiles have sensitive scales and skin. There are many pigmented domes on their skin that detect vibration. In alligators, these domes are located mostly on the face and the jaw. 

Since crocodiles cannot smell underwater, they rely on the sense of touch when hunting for fish. Movement underwater sends ripples, and the crocodiles can feel it.

A study reveals that these spots or domes have touch sensors. They are sensitive to pressure and vibration and are more sensitive to human fingers. 

Scientists who have studied these sensors call them integumentary sensors or ISOs. Over many years of research, there were several hypotheses about what these sensors are for. 

Here are some examples: 

  • Source of oily secretions to keep the crocodile clean
  • Used for detection of electric and magnetic fields 
  • Used to detect the level of salinity in the water
  • Used for detecting pressure and vibrations in the surroundings

In a study of alligators, not crocodiles, scientists found out that the gators faced the location of a drop of water, even if the pool had white noise. It means that they can detect where the drop came from.

Crocodiles are likely to do the same, but no experiments have been done to prove it yet. It is likely that they could. And if they have this detection ability, they can easily spot the location of fish or turtles swimming underwater.

Crocodile eating fish
Crocodiles hunt fish and other aquatic animals using tactile sensors called ISOs that detect movement

How is a Crocodile’s Sense of Smell so Powerful?

Crocodiles have a multi-chambered nostril and millions of olfactory receptors which can detect not only smells but the direction they are coming from. Crocodiles can smell a carcass from over four miles away using this powerful ability.

When crocodiles are on the prowl, they activate their most acute sense, which is the sense of smell. Their two nostrils have protective flaps that seal underwater.

Only the tip to be above the surface for the crocodile to breathe. It has a built-in snorkel—they have a chamber in the nostril where they can smell. There are two regions in their brain that can detect a smell that comes from the air. 

Since there are two regions, they can detect if the smell is coming from the left, right, or in front of them. 

They pick up olfactory cues from their nostrils, and then that smell travels to the brain. For scavenging, this technique is highly important. 

The scent goes in the crocodile’s nostrils, and it travels into the sensory chamber. It is in this chamber that the crocodile analyzes the smells. The chamber has millions of receptors. 

The receptors are so sensitive that they can detect airborne smells and chemicals in the water that rotting carcasses release. 

Once the crocodile has filtered the air, it continues to the lungs, and the crocodile exhales it. The power of a crocodile’s nose, or olfactory sense, is so powerful that it can detect a smell from over four miles away. 

American Crocodile
Crocodiles leave their nostrils exposed above the water to detect the scent of nearby animals

Can Crocodiles Smell Humans?

Crocodiles can smell most land animals, including humans. Some crocodiles like Saltwater crocodiles and Nile crocodiles even use this ability to hunt humans.

Nile crocodiles, in particular, are ferocious. They consider humans as prey and are not afraid to venture into human territory to find a meal. 

Since crocodiles can smell humans and detect vibrations, they can easily spot a human in the water or people doing chores by the riverbank. 

Summary

Crocodiles can smell blood in the water and in the air. However, they can only smell blood if they are on the surface. Crocodiles do not breathe underwater, which means they cannot smell when they are submerged.

If the crocodile’s snout s above the surface, it can detect smells in the water, which the air carries. Crocodiles can smell carcasses from far away, and they use this ability to find carrion, which they would eat.

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