How Do Insects Smell?

Monarch caterpillar Danaus plexippus feeding on leaf, Pennsylvania, USA
Danita Delimont / Getty Images

Insects don't have noses the way mammals do but that doesn't mean they don't smell things. Insects are able to detect chemicals in the air using their antennae or other sense organs. An insect's acute sense of smell enables it to find mates, locate food, avoid predators, and even gather in groups. Some insects rely on chemical cues to find their way to and from a nest, or to space themselves appropriately in a habitat with limited resources.

Insects Use Odor Signals

Insects produce semiochemicals, or odor signals, to interact with one another. Insects actually use scents to communicate with each other. These chemicals send information on how to behave to the insect's nervous system. Plants also emit pheromone cues which dictate insect behaviors. In order to navigate such a scent-filled environment, insects require a fairly sophisticated system of odor detection.

The Science of How Insects Smell

Insects possess several types of olfactory sensilla, or sense organs, which collect the chemical signals. Most of these smell-gathering organs are in the insect's antennae. In some species, additional sensilla may be located on the mouthparts or even the genitalia. Scent molecules arrive at the sensilla and enter through a pore.

However, simply collecting the chemical cues is not enough to direct an insect's behavior. This takes some intervention from the nervous system. Once those odor molecules enter the sensilla, the chemical energy of the pheromones must be converted to electrical energy, which can then travel through the insect nervous system.

Special cells within the structure of the sensilla produce odor-binding proteins. These proteins capture the chemical molecules and transport them through the lymph to a dendrite, an extension of the neuron cell body. Odor molecules would dissolve within the lymph cavity of the sensilla without the protection of these protein binders.

The odor-binding protein now hands off its companion smell to the receptor molecule on the dendrite's membrane. This is where the magic happens. The interaction between the chemical molecule and its receptor causes a depolarization of the nerve cell's membrane.

This change of polarity triggers a neural impulse that travels through the nervous system to the insect brain, informing its next move. The insect has smell the odor and will pursue a mate, find a source of food, or make its way home, accordingly.

Caterpillars Remember Smells as Butterflies

In 2008, Biologist at Georgetown University used odors to prove that butterflies retain memories from being a caterpillar. During the metamorphosis process, caterpillars build cocoons where they will liquify and reform as beautiful butterflies. To prove that butterflies maintain memories the biologists exposed the caterpillars to a foul odor that was accompanied by an electric shock. The caterpillars would associate the smell with the shock and would move out of the area to avoid it. Researchers observed that even after the metamorphosis process the butterflies would still avoid the odor, even though they had not been shocked yet. 

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Hadley, Debbie. "How Do Insects Smell?" ThoughtCo, Apr. 5, 2023, Hadley, Debbie. (2023, April 5). How Do Insects Smell? Retrieved from Hadley, Debbie. "How Do Insects Smell?" ThoughtCo. (accessed June 10, 2023).