The main senses that are dependent on chemoreceptors in humans and many other animals are taste and smell. Taste is the detection of certain chemical compounds from direct contact with substances, while smell is the detection of chemicals suspended in the fluid the organism occupies, whether that be water or air. In animals that breathe, internal chemoreceptors also monitor the blood levels of carbon dioxide and govern the breathing reflex.
Chemoreceptors tell organisms crucial information about their environments, informing them of threats and food sources. Humans and other mammals have very distinct senses of smell and taste, but in other organisms the chemoreceptors are not so well distinguished. Even in humans, the sense of smell has a huge role in the sense of taste, adding a large amount of information to the relatively basic sensors in the tastebuds.
While humans have taste receptors only in their mouths, other animals such as insects have them in other places, such as their feet. Similarly, animals without noses tend to have smell receptors placed elsewhere on their bodies. For some animals like earthworms, which lack any sense of sight or hearing, chemoreceptors, together with touch, are the primary way that they sense their environment.