A butterfly on a flower and a close-up of the cells that make up its eye

COMPOUND EYE: The eyes of butterflies and other insects are made up of repeating units that each contain their own light-detecting cells.

COURTESY OF ZACHARY MACDONALD (BUTTERFLY); MARTIN OEGGERLI/SPL/SCIENCE SOURCE (EYE)

STANDARDS

NGSS: Core Idea: LS1.D, LS4.C

CCSS: Literacy in Science: 7

TEKS: 6.2A, 7.2A, 8.2A, B.2E

Butterfly Vision

An experiment sheds light on how butterflies find their way

AS YOU READ, THINK ABOUT how animals use their senses to navigate.

COURTESY OF ZACHARY MACDONALD

Butterflies bob and weave as they flutter through the air, going one way and then, all of a sudden, another. To a person, this flight can appear aimless. But butterflies really are trying to get somewhere: They’re searching for the ideal habitat to live, feed, and reproduce.

How, exactly, do seemingly bumbling butterflies navigate? That’s what Zachary MacDonald, a biology graduate student at the University of Alberta in Canada, wanted to find out. Other species don’t always perceive the world the way humans do. He knew it would be a challenge to determine whether butterflies rely on vision or other senses—like smell—to find a suitable home. Luckily, MacDonald had a flash of inspiration about how to investigate the mystery.

One day, MacDonald was taking close-up photos of butterflies he was studying. He wondered if the camera’s flash was blinding them. If you’ve ever had a bright light flashed in your eyes, you may have seen spots afterward that made it hard to see. This temporary loss of vision is called flash blindness. It occurs when light overwhelms the light-detecting photoreceptor cells in your eyes. MacDonald thought he might be able to use the same phenomenon to learn whether butterflies depend on their eyes to find their way.

Butterflies bob and weave through the air. They flutter one way, and then they suddenly go another way. This flight can appear aimless to a person. But butterflies really are trying to get somewhere. They’re searching for the right habitat to live, feed, and reproduce.

How do the fluttering butterflies find their way around? Zachary MacDonald wanted to find out. He’s a biology graduate student at the University of Alberta in Canada. Other species don’t always experience the world the way humans do. Do butterflies use vision or other senses, like smell, to find a good home? MacDonald knew it would be a challenge to learn the answer. Luckily, he had a flash of inspiration about how to investigate the mystery.

MacDonald was already studying butterflies. One day, he was taking close-up photos of them. He wondered if the camera’s flash was blinding them. If a bright light flashes in your eyes, you may see spots afterward. For a while, it’s hard to see. This temporary loss of vision is called flash blindness. It occurs when light floods the photoreceptor cells that detect light in your eyes. MacDonald thought he could use flash blindness to learn if butterflies depend on their eyes to find their way. 

CATCH AND RELEASE

For his experiment, MacDonald used nets to catch dozens of wild Speyeria cybele and Speyeria atlantis butterflies. He placed them in a dark cooler to keep them calm. Then he boarded a boat and took the cooler to a spot in a nearby lake where only one island was visible.

For half of the butterflies, MacDonald triggered intense camera flashes above, below, in front of, behind, and on both sides of their eyes. Insects’ compound eyes consist of thousands of units called ommatidia. “They face in almost all directions,” says MacDonald. “So, we wanted to make sure that we exposed all of them to the flash.” Then he released all the butterflies— those that had been exposed to camera flashes and those that hadn’t—one by one.

MacDonald caught dozens of wild Speyeriacybele and Speyeriaatlantis butterflies in nets for his experiment. He placed them in a dark cooler to keep them calm. Then he got on a boat and took the cooler out onto a nearby lake. Only one island could be seen from this spot.

MacDonald set off strong camera flashes for half of the butterflies. He flashed above, below, in front of, behind, and on both sides of their eyes. Insects have compound eyes. They’re made of thousands of units called ommatidia. “They face in almost all directions,” says MacDonald. “So, we wanted to make sure that we exposed all of them to the flash.” The other half of the butterflies weren’t exposed to camera flashes. Then he released all the butterflies, one by one.

LARRY WEST/FLPA

FINDING MY WAY: A Speyeria cybele butterfly

LAND AHOY!

Most of the butterflies that hadn’t been exposed to flashes soon spotted the island. “You could tell when they found it, because they just flew directly to it,” says MacDonald. But the flashed butterflies fluttered around randomly. The few that did find the island seemed to do so by chance.

MacDonald repeated the experiment farther from the island with similar results. The butterflies were navigating mainly by sight. We can never know exactly what it’s like to be a butterfly, says MacDonald, but science can provide clues to how these organisms experience the world.

The butterflies that hadn’t been flashed took off. Soon, most of them spotted the island. “You could tell when they found it, because they just flew directly to it,” says MacDonald. But the flashed butterflies fluttered around aimlessly. A few found the island, but they seemed to find it by chance.

MacDonald repeated the experiment farther from the island, and he got similar results. The butterflies were finding their way mainly by sight. We can never know exactly what it’s like to be a butterfly, says MacDonald. But science can provide clues to how these creatures experience the world.  

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