A MOTH IN THE NIGHT SKY

The leaded window opened
To move the dancing candle flame
And the first moths of summer
Suicidal came.
--Ian Anderson (Moths)

My eyes say their prayers to her
Sailors ring her bell
Like a moth mistakes a light bulb
For the moon and goes to hell.
--Tom Waits (Black Market Baby)

Thus hath the candle singed the moth.
O, these deliberate fools! when they do choose,
They have the wisdom by their wit to lose.
--William Shakespeare (The Merchant of Venice)

What natural phenomenon could have possibly inspired more poetry, literature and song than the headlong dash of the moth for the flame? References to it can be found in the religious mythology from any part of the world, and it doesn't take much imagination to picture our ancestors mixing moth metaphors around a Neanderthal campfire. Yet for all its history of human fascination, it's a curiosity that we still don't understand at all.
Positive phototaxis is the technical term for an organism's attraction toward light. It's been well studied among photosynthetic bacteria, where it's obviously beneficial, but its advantages for the insect hurtling into a fiery death are less clear. Some have postulated that it's linked to lunar navigation, but this seems unlikely to me. Others claim that flying toward a light source keeps moths from crashing into the ground. University of North Carolina medical technologist Henry Hsiao put forth an interesting theory concerning the Mach Band, an optical illusion well known to painters, where a harsh line between darkness and light produces an apparition of two bands, one light and one dark. Hsiao asserted that moths fly into the dark Mach band in an attempt to evade the light, which puts them into orbit around a terrestrial light source—a marvelously creative explanation. To my mind, the most logical hypothesis posits that moths fly perpendicular to light radiation. Under a normal night sky, this keeps them flying horizontally, but will cause them to circle about a candle if that is the brightest light source.
Whatever is actually going on inside their little cerebral ganglia, the lights of the city have changed nighttime reality for moths and for many other creatures as well. Prone to a form of phototaxia myself, I often find myself drawn to lights in search of interesting insects. While working at a Costa Rican biological station, I began each morning by checking a black light screen set up specifically to attract insects. I have a number of favorite “nocturnal birdfeeders”--a lamp not far from my house is a dependable spot to observe our largest local bat, the Hoary Bat (Lasiurus cinereus), and most summers I visit an isolated streetlamp in the Mojave to watch Lesser Nighthawks (Chordeiles acutipennis). What is a resource, though, to certain nocturnal nature-watchers and insectivores, is a decided threat to others. Many insects live as adults only to breed. Many of these, like the giant silk moths of the family Saturniidae, do not feed as adults, and live but for a few days. Many of these insects have become incredibly scarce as the adults have come to devote those precious hours not to mating, but to dashing their head against a hot bulb. Twenty years ago, I rented a house in the center of about 100 acres of undeveloped land surrounded by city. A couple of years into my stay, a grocery store was built on part of that land. That summer I visited the store every evening to admire the astonishing variety of moths and other insects that perched upon a brightly illuminated back wall. Subsequent years have brought but a few common species to the wall—a statistically insignificant anecdote, but still I assume those lights were responsible in part for eliminating a good chunk of the neighborhood's insect fauna during that first summer.

Each year the night skies brighten, with fewer vantages from which to appreciate the Milky Way. Twenty years ago, most of my favorite regional haunts were impossible to negotiate on moonless nights. Today it's possible to read a book in most of them. For thousands of years we've marveled at the seductive pull of the moth to light without adequately explaining it, and we remain just as clueless to its implications. Like so many of the changes we introduce, the ecological impact of city lights can only be fathomed by recording it as it occurs.
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upper: ATLAS MOTH (1999) watercolor 15" x 10.5"
center: NUTTALL'S SHEEP MOTH (1998) acrylic 5" x 3"
lower: GLOVER'S SILK MOTH (1998) acrylic 9" x 7"