The Attraction of Blood: What Component Lures Carnivorous Animals

What does blood smell like to predatory animals? While humans find the smell unpleasant, for carnivores it smells like food. Now, scientists have taken a look at which substances of blood trigger behavioral reactions in predatory animals.

"For predators, food scents are particularly attractive, and much of this has to do with blood," said Matthias Laska, one of the researchers, in a news release. "We wanted to find out which chemical components create the scent of blood."

In this case, the researchers searched for the contents of volatile substances in mammalian blood. Yet at first, they found nothing.  Then, a master's student analyzed mammalian blood with the help of gas chromatography and mass spectrometry, which could separate and identify chemical compounds in a sample. The machine detected 30 substances in total, and some of these were decomposition products from fats. The researchers also employed human scent experts who identified additional smells that the gas chromatograph missed.

One substance in particular stood out, an aldehyde called trans-4, 5-epoxy-(E)-2-decenal. This substance emits the typical metallic scent that humans associate with blood.

In order to test whether this was the scent that predators were attracted two, the scientists infused wooden logs with four different liquids-aldehyde, horse blood, fruit essence and a near-odorless solvent. Then, the researchers exposed four predator species-Asian wild dogs, South American bush dogs, African wild dogs and Siberian tigers-to the scents.

The scientists found that the logs containing aldehyde were just as attractive as those containing blood. The two remaining logs aroused little interest. The most common behaviors included sniffing, licking, biting, pawing and toying. In the end, it seems that a single component can be just as attractive as a complex odor.

"How this developed through evolution is an interesting question," said Laska. "Perhaps there is a common denominator for all mammalian blood."

The findings are published in the journal PLOS One.