By Dr. Becker
Butterflies are amazing for a number of reasons, not the least of which is their sophisticated color vision. Up until recently, the golden birdwing butterfly held the record for having the largest variety of photoreceptors, or light-detecting cells, in their eyes — nine.
There was reason to believe that common bluebottle butterflies, a species of swallowtail butterfly from Australasia, also have exceptional vision.
For instance, according to researchers from SOKENDAI (The Graduate University for Advanced Studies) in Japan, the butterflies typically have large compound eyes, fly very fast and visit puddles and colorful flowers often.
In addition, they have vibrant wing coloration, including a blue-green iridescent band mid-way through, which the researchers believed “must be crucial for visual signaling.”1
Still, when researchers studied the common bluebottle’s eyes, they made a surprising discovery: they contain at least 15 photoreceptors, which are comparable to the rods and cones in human eyes. The researchers wrote in the journal Frontiers in Ecology and Evolution:2
“Butterflies typically have a rich variety of spectral receptors in their compound eyes. We found 15 distinct photoreceptor types in the eye of G. sarpedon [common bluebottle], which is a record among all insects studied so far.
Stomatopod crustaceans, which have up to 16 spectral classes of receptors in their eyes, have been considered to be exceptional, but our finding of an almost equal level of spectral richness in a butterfly challenges this view.”
Butterflies May Have Visual Advantages Over Humans
Butterflies’ highly developed and sensitive vision likely gives them a survival advantage. For starters, the multiple photoreceptors help the insects to see in color, as each class of photoreceptors helps them to distinguish between different colors. According to The Christian Science Monitor:3
“Humans typically have just three classes of cones in their eyes, but that enables them to view millions of colors. Many other insects also use only three classes of photoreceptors and manage to have effective color vision. In that regard, the researchers believe the butterfly species is similar.”
In fact, the recent study revealed the common bluebottle butterfly uses four photoreceptor classes to detect color.
The other 11 photoreceptor classes are likely used to give the butterflies other visual advantages that in some ways extend beyond human vision, like detecting fast-moving objects against the sky or finding colorful objects hidden amongst different backdrops.
Lead study author Kentaro Arikawa, Ph.D., professor of biology at SOKENDAI, said in a press release:4
"Butterflies may have a slightly lower visual acuity than ourselves, but in many respects they enjoy a clear advantage over us: they have a very large visual field, a superior ability to pursue fast-moving objects and can even distinguish ultraviolet and polarized light.
Isn't it fascinating to imagine how these butterflies see their world?"
Seeing in Butterfly Vision
Butterflies see the world in a very different way from humans. Their compound eyes are made of thousands of tiny “eyes” called ommatidia. Each ommatidium has its own lens, cones and retina cells, and each is set at a slightly different angle from the next.
According to the Museum of Science and Industry (MOSI), Tampa, Florida, “This arrangement allows the butterfly eye to simultaneously see in all directions at the same time with a mosaic of individual images that form a whole picture. This type of vision is known as Omni-vision.”5
This is truly amazing, as it means butterflies can see and feed on a flower, while at the same time having a clear view of butterflies to their left and right, and any predators that may come up behind them.
Also unique, butterflies see in tetrachromatic vision compared to humans’ trichromatic vision. Butterflies can see many colors that humans can as well as some that we can’t. There are also differences in color vision among different butterfly species.
Some, for instance, can determine the difference between red and green while others cannot. Research has also shown that some butterflies detect ultraviolet (UV) colors and express a UV-yellow pigment on their wings. MOSI explained:6
“Invisible to the human eye, this pigment may help butterflies detect appropriate mates so they have more time to eat, rest, lay eggs and thrive.
Species that look very similar to us likely look very different to butterflies who can use the UV markings to quickly determine if another butterfly is of their same species or not.”
Treat Your Eyes to a Beautiful Sight: More Butterflies in Your Backyard
Habitat destruction has led to declines in many butterfly species and some are now endangered. North America’s iconic orange-and-black monarch butterflies are among those vulnerable to extinction.7
Due to the increased use of herbicides like Roundup on genetically modified crops, milkweed is disappearing. The monarch butterfly cannot survive without the ample presence of milkweed.
This perennial plant is the only plant on which the monarch will lay its eggs. Once the larvae hatch, the caterpillar eats the plant. Without milkweed along its migratory path, the monarch simply cannot reproduce.
Like monarchs, the larvae of the Oregon silverspot butterfly, also a threatened species, also rely on just one single host plant to survive — in this case the western blue violet. As its habitat has disappeared, so too has the population — in droves.8
This is a familiar story among butterflies, unfortunately. The Karner blue butterfly is another example. Karner blue catepillars only feed only on the leaves of the wild lupine plant, and due to habitat loss and degradation, this species is also endangered.9 You can make a difference by planting butterfly-friendly plants in your backyard. When you do, you’ll be treated to a spectacular show as beautiful butterflies appear seemingly out of nowhere. Plants that will attract and help support butterflies:10
✓ Bee balm
✓ Butterfly weed
✓ Purple coneflower
✓ New England aster
✓ Black-eyed Susan
✓ Butterfly flower
✓ Purple ageratum