Jacobson’s organ is found in the roof of the mouth in reptiles and mammals. It is also called the vomeronasal organ. This organ works by detecting chemicals such as pheromones.
Some species of bats do not have a fully functioning Jacobson’s organ.
Pheromones are the chemical substances that a living organism emits and that organisms of the same species can detect. Scientific research has revealed that plants, vertebrates, and insects communicate in this chemosensory way. For example, the female silkworm signals potential mates by releasing the pheromone bombykol, first discovered in 1959 by Adolf Butenandt. When bees form a swarm, it is in response to other bees that they emit pheromones as an alarm.
Elephants play the Jacobson organ with their trunks.
Reptiles and mammals use Jacobson’s organ to detect pheromones. Elephants touch this organ with the tip of their trunk to carry out their chemosensory perception of things. A lion uses it to detect sex hormones and often opens its mouth to smell the pheromones it detects.
Jacobson’s organ also helps some animals perceive chemical compounds other than pheromones emitted between species. For example, snakes find their prey using it. A snake places its tongue in the two nostrils in the roof of its mouth after having its tongue in the air to allow it to properly sense the direction of its prey. The reason snakes have forked tongues is so that the tongue can touch these holes. The deeper the fork goes into the snake’s tongue, the more the snake uses its Jacobson’s organ.
Snakes have a fully functional organ, but humans and some bat species do not. The vomeronasal organ develops in the fetus but does not continue to fully develop. Researchers have found that some people may have at least one partially functioning organ, but other researchers consider that only a fully functioning Jacobson’s organ has one, so these results are controversial.