Navigation: Steering

Navigation: Steering the Course

Butterflies, like other diurnal creatures, rely on the sun and visual clues to navigate. Their internal circadian clock integrates the information gathered by the eyes, which is then processed by the brain to determine their location. Because the sun is constantly moving, the brain must constantly recalculate the animal’s position relative to the sun. Butterflies can also see polarized light, a visual clue to the flower’s “landing strip” and nectaries. Like us they have two eyes, but while we have but two lens, each butterfly ‘s compound eye has up to 17,000 lens. This creates a visual field of about 340 degrees that allows them to see predators coming from any direction. However, they cannot triangulate to estimate distances as we do. Most amazingly, their brain, which is the size of a pin head, can instantaneously process and act upon the data from the 34,000 lens of the two eyes.

Long-Distance Navigation

When I moved to Kansas in 1981, a shimmering orange curtain moved across the Kansas sky in September. I ignored it, unaware of its beauty and significance. Now, I sadly search the sky for a glimpse of Monarchs still making their way, but they fly south one by one, rather than millions of individuals. Monarchs are genetically programmed to fly southwest each fall and fly back northeast each spring. The position of the sun tells them when to begin their journeys but how do they know the exact route and the destination? The Monarch’s southern destination, an oyamel fir forest near Mexico City, was not discovered by humans until 1975! A few other North American butterflies migrate, including Painted Ladies, Buckeyes, Gulf Fritillaries and Cloudless Sulphurs. Each species has its own unique route and destination.

Notes from the Laboratory

Scientists have long sought to understand the Monarch’s navigational capabilities that allow it to make a round trip journey of up to 6,000 miles. Experiments have included putting migrating Monarchs in dark boxes for a week or two. When released, they fly in the wrong direction. But there is more to navigating than the eyes and the brain. If the antenna are painted with light-blocking black enamel paint or surgically removed, the butterfly is unable to orient to a southern direction. However, Monarchs with clear-painted antenna have no trouble navigating. Also, researchers have discovered that tiny bits of the metal magnetite are embedded in the tissues of the long-distance migrants such as birds, sea turtles, whales and Monarchs. And laboratory experiments demonstrate that if the earth’s normal magnetic field is reversed, then Monarchs reverse course. If there is no magnetic field present, the Monarchs fly aimlessly, unable to set a course. Obviously, the magnetic field-sensing antennae are part of an entomological global positioning system.

The monarch’s migration is unique among insects because the same female flies from North America to Mexico and then returns to the U.S. to lay her eggs. Map courtesy of Monarch Watch.

In fall Monarchs fly in mass and even find the same nighttime roost trees every year! The antennae, brain, eyes and microscopic bits of magnetite comprise the Monarch’s navigational equipment.

Photos by Lenora Larson.

The Lepidopteran GPS

Current evidence points to butterflies having two clocks! The brain-based circadian clock is linked to the sun by the eyes. An antenna-based clock links to the earth’s magnetic field and signals the brain if the insect slides off course by even a percent of a degree. This amazing biological system works more efficiently than our human mechanical GPS system.

LENORA LARSON Butterfly Maven

A Marais des Cygnes Master Gardener, Lenora is a member of the Idalia Butterfly Society and Kansas Native Plant Society. She gardens in the clay soil and cruel winds of Paola, KS. She may be contacted at lenora.longlips@gmail.com.