Fear has its own smell. It comes from what scientists call an "alarm pheromone."
Animals produce it when they're stressed, but how it works has long puzzled scientists. Now, a team in Switzerland has discovered an organ in the nose of mice that detects alarm pheromones — in effect, it smells fear.
The organ, known as the Grueneberg ganglion, is a tiny bundle of cells near the tip of a mouse's nose.
Marie-Christine Broillet, a biologist at the University of Lausanne, collected air samples from cages where older laboratory mice were being euthanized. When researchers exposed a live mouse to that air, the neurons in the Grueneberg ganglion started to fire. And the mouse's behavior changed. "It would just go to the opposite end of the cage and freeze," says Broillet.
In another experiment, Broillet's team removed the detection cells from mice. Then, the pheromone didn't seem to scare them at all.
Another type of animal that uses alarm pheromones is fish. When a fish is attacked by a bigger fish, a substance called "schreckstoff," a German word that translates as "shriek stuff," is secreted from its skin.
Nathaniel Scholz, a zoologist with the National Oceanic and Atmospheric Administration, studies how pollution affects the ability of fish to smell fear.
"We're focused on this area because there are a lot of different pollutants that run off terrestrial landscapes in storm water and get into fish habitats," he says. "And because the nose is exposed to the environment, water pollution can effectively interfere with the normal functioning of the nose."
Scholz has found that copper in urban runoff prevents fish from smelling the alarm pheromone.