In humans, the sense of smell often seems to play a lesser role than sight, hearing or touch. However, its performance is noticeable when olfactory perception is lost, for example when you have a cold.
Such a condition would be life-threatening for many wild animal species, since they rely on their sense of smell in a number of ways. Because the smells or scents that can only be perceived with this serve to identify food, spoiled (rotting) or decomposed (carrion odor), to distinguish one's own body odor from that of familiar group members (stable odor) and from that of foreign conspecifics as well as from that of other species , the warning of enemies (predator) or the assumption of prey (prey animal).
Olfactory perception is therefore not only important for food intake, but also plays an important role in social behavior and mating behavior. The sexual maturity of females is signaled to males by pheromones (sexual attractants). In addition, fragrances also help with spatial orientation. Many animals use scent marks to demarcate a territory or, like ants, follow the scent trail of their predecessors. In addition, chemical signaling substances can also be used for communication between different species. For example, the flowers of many plants emit fragrant substances that attract insects, which they then pollinate (allomon) or just collect nectar (kairomon) or do both (synomonic). The effect of pheromones is used to combat pests in orchards, for example to limit the mating of plum moths.
Various sensory systems can be involved in olfactory perception: in addition to the actual olfactory system (smell stimuli), the nasal-trigeminal system (tactile and chemical stimuli) and influences of the gustatory system (taste stimuli).
The sense of smell is the most complex chemical sense.
The olfactory sensory cells are equipped with specific olfactory receptors and are usually located in the nose in vertebrates. Some smells are not consciously perceived (see also Jacobson's organ).