Monarch butterflies are one of the most recognizable and beloved butterflies in North America. Their vibrant orange wings with black veins and white spots make them unmistakable. Monarchs are well known for their epic annual migration from the United States and Canada to overwintering sites in central Mexico—a journey of up to 3,000 miles.
One aspect of monarch butterfly biology that is less well known is their color vision and color preferences. Like many insects, monarch butterflies can see wavelengths of light that humans cannot, including ultraviolet light. This affects what colors they are attracted to and which flowers they preferentially visit. Understanding what attracts monarchs can help us provide the resources they need throughout their complex life cycle.
Monarch Butterfly Vision
Monarch butterflies have compound eyes, like all insects. Their eyes contain photoreceptor cells that are sensitive to different wavelengths of light. There are three types of photoreceptors in monarch eyes that allow them to see color:
- Ultraviolet (UV) receptors—sensitive to UV light
- Blue receptors—peak sensitivity around 440 nm wavelength
- Green receptors—peak sensitivity around 540 nm wavelength
Having three types of color receptors means that monarch butterflies have trichromatic vision. This allows them to distinguish different colors based on the relative stimulation of the three photoreceptors. It also expands the range of colors they can see compared to humans, who only have receptors for red, green, and blue light.
Butterfly eyes are also specialized with ommatidia, the individual units containing the photoreceptor cells, arranged in a mosaic. This gives them increased sensitivity to certain colors in parts of their vision field, helping them hone in on important cues like food sources.
Monarch Butterfly Color Preferences
Given their ability to see ultraviolet light, what colors are monarch butterflies actually attracted to? Understanding their preferences can help illuminate an important part of their sensory world.
Research into monarch color vision has investigated this through several approaches, including analyzing their eye structure, testing behavior, and observing flower visitation.
One pioneering study looked at monarch ommatidial mosaics under a microscope. They found the highest density of UV and blue receptors pointing upward, suggesting heightened sensitivity to UV, violet, and blue tones from elements like the sky. Green receptors were more prominent equatorially, perhaps allowing them to spot green foliage.
Behavioral studies have also gleaned insights through offering monarchs choices of colored cards and observing their reactions. These tests have shown preferences for violet and blue shades. In one study, the most attractive color was a reflective blue with a violet tinge.
Analyzing what flowers monarchs visit in the wild provides additional real-world data. Orange, yellow, pink, purple, blue, and white flowers attract the most monarch traffic. Visits increase with higher levels of anthocyanins, pigments that reflect UV and violet-blue light. This draws monarchs visually.
Why Are Monarchs Attracted to Certain Colors?
The preference of monarch butterflies for violet, blue, and UV reflective colors is likely driven by two main factors:
Finding Food Sources
Many of the flowers that monarchs visit offer nectar that fuels their energy needs. Brightly colored blooms act as visual advertisements to attract pollinators. Reflective petals in the UV and blue range are highly visible to monarchs zipping by. Spotting these flowers helps monarchs efficiently find nectar sources.
Locating Milkweed
Monarchs cannot complete their life cycle without milkweed plants. Females only lay their eggs on milkweed, which their caterpillars consume. Monarchs may be able to locate milkweed more quickly by keying in on the UV-absorptive white and yellow blooms produced by many milkweed species.
Research has found that floral guides on milkweed flowers—UV-absorbing lines that point to nectaries—are only visible under UV light. This draws monarchs to productive feeding areas.
How Color Affects Monarch Conservation
Understanding monarch color preferences has important implications for conservation. With monarch populations declining, efforts are underway to provide the habitat resources they need, especially milkweed for breeding. Strategically incorporating colors favored by monarchs into gardens and public landscaping could increase the use of these areas by monarchs.
For example, clustering blue and violet flowers near milkweed plants may help attract more monarchs there to lay eggs. Leaving UV-reflective native wildflowers will also draw in adults seeking nectar. Avoiding cosmos, marigolds, and other yellow/orange flowers may prevent monarchs from being distracted from the milkweed.
Raising awareness of the monarch visual world can inspire the public to make butterfly-friendly plant choices. Their appreciate of color also underscores the intertwined nature of sensation and survival for these iconic insects. Even a butterfly’s sense of color is specialized for its unique lifestyle and needs.
Conclusion
Monarch butterflies have specialized color vision that includes sensitivity to ultraviolet wavelengths. Behavioral and ecological evidence indicates that monarchs are preferentially attracted to violet, blue, and UV reflective colors, rather than warm yellow and orange hues. These color preferences likely guide monarchs to find nectar-bearing flowers and critical milkweed plants. Consideration of the monarch visual system and color choices can inform conservation efforts aimed at supporting monarch breeding, feeding, and migration. By providing their favored flower colors, we can create landscapes that better provide for the distinctive needs of monarch butterflies.
| Color | Attractiveness to Monarchs |
|---|---|
| Orange | Low |
| Yellow | Low |
| Blue | High |
| Violet | High |
| UV Reflective | High |
