Scent is an important navigational tool for butterflies, working alongside their strong visual acuity to locate vital resources. While bright colors help them spot potential flowers from a distance, odor confirms the presence of nectar and guides their final approach. Different butterfly species respond to distinct chemical signals for feeding, finding mates, and locating suitable host plants for their young.
How Butterflies Detect Odor
Butterflies do not possess a nose like mammals, instead sensing their chemical environment through specialized sensory structures called chemoreceptors. These receptors are densely concentrated on the clubbed ends of their antennae, which are constantly waved in the air to sample volatile organic compounds (VOCs). Chemoreceptors function like a lock-and-key system, where specific airborne chemical molecules fit into receptor sites, sending a signal to the butterfly’s nervous system.
The maxillary palpi, small, sensory appendages near the mouth, also contain chemoreceptors that contribute to the sense of smell and taste. Female butterflies have additional chemoreceptors located on their tarsi, or feet. They use these to test the chemical composition of a plant upon landing, allowing them to identify the appropriate host plant for laying eggs.
Floral Scents: The Primary Nectar Signal
The scents flowers emit to attract butterflies are complex blends of volatile organic compounds, which signal a rich source of nectar. These chemical profiles are often perceived by humans as mild and pleasant, contrasting with the strong, sometimes musky, odors designed to attract nocturnal moths. The dominant chemical classes in butterfly-pollinated flowers include benzenoids, monoterpenes, and various alcohols and esters.
Specific compounds frequently found are phenylacetaldehyde and 2-phenylethanol, which are benzenoids associated with a sweet or honey-like scent. Linalool and its oxides, which are monoterpenes, are also strong attractants, lending a light, floral, or citrus-like note to the blend. The overall scent profile is more important than any single molecule, as butterflies are typically drawn to a specific combination of VOCs that indicates a reliable nectar reward.
Non-Floral Attractants: Host Plants and Pheromones
Not all attractive scents are associated with feeding, as butterflies also respond to odors related to reproduction and survival. Female butterflies utilize specific plant odors to locate host plants, which are the only plants their larvae can eat. These host plant cues often involve chemical compounds that are bitter or sulfurous, which are distinct from the sweet-smelling nectar signals. The female will test the plant’s surface chemicals with her leg chemoreceptors before committing to lay her eggs.
Pheromones represent another important class of non-floral attractants. Male butterflies produce these species-specific scents to attract females during courtship, often dispersing them from specialized scent scales on their wings. These pheromones are chemically diverse, including alkaloids, terpenoids, and fatty acid derivatives, and are generally effective only over short distances. Pheromones provide the final, species-confirmation signal.
Maximizing Scent Attraction in Gardens
To create a garden that maximizes scent attraction, gardeners should focus on concentrating volatile organic compounds to make them more noticeable. Planting highly fragrant nectar sources in large, dense clusters, or masses, helps to create a stronger, more easily detectable scent plume. This concentration ensures that the chemical signals travel further and are more appealing to passing butterflies.
Scent intensity can also be amplified by careful placement, such as positioning fragrant plants in sunny, sheltered spots. Warm, still air helps to hold and disperse the scent, creating clear scent corridors that butterflies can follow. Considering the time of day is also helpful, as some flowers release their most intense fragrance during the warmest hours when butterflies are most active. Avoiding the use of strong chemical pesticides and herbicides is necessary, as these scents can repel butterflies and interfere with chemoreceptor detection.