Blood Odor Chemical Leaves Predators Drooling

We've seen it in the movies: a man-eating carnivore staring down its prey while saliva drips from its fanged mouth. Now, new research says this isn't exactly accurate, as it's not the smell or sight of prey that gets a hunter drooling. Instead, it's a chemical in blood that carnivores find mouth-watering.

The chemical is called trans-4,5-epoxy-(E)-2-decenal, and it's apparently found in almost all mammal blood, giving the sometimes sticky substance its own distinct odor. This odor, while alarming for some animals, signals to predators that it's meal time, prompting a boost in activity from a carnivore's salivary glands to aid in the digestive process.

To make sure that it was the smell of blood, not the sight of injured and easy prey, that drove predators wild, a team of researchers and odor experts assessed the behavior of several large carnivores. They presented with a log that was soaked with mammal blood - a pure blood-odor chemical, a fruity odor chemical, or a odorless solvent.

After observing captive Asian wild dogs (Cuon alpinus), African wild dogs (Lycaon pictus), South American bush dogs (Speothos venaticus), and Siberian tigers (Panthera tigris altaica), the researchers determined that the animals were far more likely to start excitedly sniffing, drooling and biting when exposed to a blood a blood chemical infused log.

"Most importantly, no significant differences were found in the number of interactions with the wooden logs impregnated with mammalian blood and the blood odor component in any of the four species," the researchers noted.

This, they argue, implies that trans-4,5-epoxy-(E)-2-decenal may be a universal "character impact compound" of mammalian blood odor for all predators, no matter the size, shape, or region.

This can also explain who some predators, like sharks, evolved to detect the scent of blood from even great distances away.

The results can be found in a study published Monday in the journal PLOS One.