Rigor Vitae: Life Unyielding

Monday, March 20, 2006


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.
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"


Anonymous Anonymous said...

It is very interesting that something as "simple" as city lights can have such an impact on the ecosystem.

10:02 PM  
Anonymous Anonymous said...

WOW! I am happy to have found such an interesting blog. I apppreciate the beauty and intelligence found here.

5:03 AM  
Blogger Carel Brest van Kempen said...

DAPFD, OD and BB: Thanks for your nice comments. For a nocturnal animal, light pollution changes the environment as profoundly as acid rain or greenhouse gases.
igcorrec: Great comment spam! Hey, where's that word verification button?...ah, here we go...

6:09 AM  
Anonymous Anonymous said...

visit me

9:58 AM  
Anonymous Anonymous said...

Just Great...

11:28 AM  
Anonymous Anonymous said...

OFF TOPIC: "failed field biologist" -- really funny line

2:17 PM  
Anonymous Anonymous said...

The constraint on speculations about moths and flames is this: "moth brain" - as in very small. Remember that a moth doesn't eat, has a fun but brief sex life, and acts primarily as the dispersal agent for creating new catepillars. Dispersal is accomplished not by moth power, which is good for a few horizontal kilometers in a moth life, but by wind power, which is good for blowing moths many hundreds of kilometers in one night. So moths fly up, not to candles or streetlights, but toward the moon. That puts them into strong winds, and at dawn they descend far from where they started, hopefully onto good and uncrowded moth habitat. There is no attraction to candles, moths mistake the brightest light to be the moon. Now consider the moth carnage of light pollution and be sad.

12:26 AM  
Blogger Carel Brest van Kempen said...

Máis alá & Mediátika-transfer: Boa vinda! !Bienvenidos!
Jim: Thanks. Glad you like it.
Akenhead: Nicely said. For me, your description falls under the "keeping from hitting the ground" category of explanations. Thanks for taking that into greater detail. Of course it doesn't apply to many moths, like the Sphingid moths that spend their adult lives feeding on nectar and flying powerfully from one flower to another.

9:25 AM  
Anonymous Anonymous said...

gorgeous moth pictures

9:51 AM  
Anonymous Anonymous said...

I love the moth images also! Butterflies always get all the press because they are flashy and sexy. But moths kick ass.

If you put a moth under an Scanning Electron Microscope like I have, you know just how complex and pretty it is.


10:25 AM  
Anonymous Anonymous said...

Yet another great post down the path of thought less trod.

Every night I spend far out in the Gulf of Mexico, I think "you can't pay for views of the stars this good." I have a completely new way of looking at moths...

2:08 AM  
Anonymous Anonymous said...

I just read a study out of a school in the US that documented the navigational aspect of the moth, and its use of the light to replicate the moon.

according to the study, the moths evolved using the lunar sky to navigate. the problem is that the moon is large and far away, while a light source seems large (if you're viewing it as the moon) but is not far away. so it hits it.

it never evolved to assume it would bump into the moon. it has no 'off' button for that.

good luck tracking it down, sorry i can't be of any help with it.

i did hear about the study about 7 months ago on a CBC program (www.cbc.ca)

1:48 PM  
Blogger Carel Brest van Kempen said...

Robotmadder: Thank you! I hope you drop by again.
Alex: Thanks for the tip; I'll bear that in mind next time I have access to an electron microscope.
RGS: Nice to have you back again. I'll bet the night sky is spectacular out at sea. This landlubber has never been more than a couple of miles from shore.
Fergus: Thanks for the information. I've seen some similar papers, but I'm not convinced that lunar navigation is a major part of the picture.

6:29 PM  
Anonymous Anonymous said...

ahhh, paintings after my own heart.. wonderful.

(Enjoyed your illustration of how the desert tortoise painting came to life too)

9:32 AM  
Anonymous Anonymous said...

This comment has been removed by a blog administrator.

9:47 PM  
Anonymous Anonymous said...

What a beautiful analogy of the moths/light and the humans/light. I enjoyed the poetry and the science. I love when literature and science meet, and what a great job you've done. The mach band was interesting too.

5:25 PM  
Anonymous Anonymous said...

I forgot to mention that when I lived in Colorado, there was serious concern about the habits of mountain lions having changed due to the light pollution. You've probably read about this. I can't remember the details now, but it was quite interesting the way they linked an increase in mountain lion/human encounters with light pollution.

5:28 PM  
Anonymous Anonymous said...

Actually, there are some moths that are most definitely using the moon for navigation--so precisely, in fact, that they shift their bearing 16 degrees every hour or so to account for the slow movement of the moon across the sky (and it would be some coincidence if this shifting in their navigation over time just happened to match the rate and angle of the moon's movement across the sky!). Amazing stuff...

6:04 PM  
Blogger Carel Brest van Kempen said...

Amazing, indeed. I'll have to look into that. Thanks for the information.

9:39 PM  
Anonymous Anonymous said...

Moths, butterflies and insects in general... ALL are in decline. Being at the base of the food chain higher order creatures (consumers) are dying as a result. Light at night, LP, sucks them from habitat areas like a vacuum cleaner. So then it is no surprise bugs and birds are disappearing. You can read more at http://www.lightpollution.org.uk
The 24 hour day is killing off Life On Earth. Do you care? Will we be JIT - Just In Time? Personally I am beginning to believe that we may well be JTL - Just Too Late.

1:26 PM  

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