I've been wondering...

[Mark Walker]

Paul Johnson wrote:


> Actually, in spite of the evidence of our eyes, most moths are
>not attracted to light, but they do navigate by light sources (moon and
>stars would be the natural sources for a moth flying at night).  the
>phenomenon is called a "light compass," and invovles flying at a constant
>angle to a very distant light source in order to maintain a straight
>flight path.  When the source is nearby (such as our porch lights), they
>spiral into the light as they constantly adjust their angle of flight.
> They eventually arrive, somewhat confused, in the vicinity of the
>light source.

This is, of course, a recurring thread and a question that remains
unanswered as far as I'm concerned.  I've got lots of anecdotes that tend to
refute Paul's explanation, but one experience that I had just last night is
particularly interesting.

I was visiting some friends who have a cottage overlooking Lake Bomoseen in
central Vermont last night.  As we were sitting in a well lit screened
porch, a large Sphingid flew up to the screen, bumping and hovering it's way
around.  I was about to go outside to get a better look at it when my friend
suggested I use a flashlight to navigate my way down the sloping bank below
the porch.

Before going outside, I turned the light on and flashed it towards the moth.
It's reaction was to fly away from the screen (into the darkness beyond),
only to return after I turned out the light.  We played this game for a few
rounds, and then I went outside to get a better look.

After scrambling down a 15 foot embankment, I realized I was too far below
the screen to get a look.  I pointed the light up towards the moth anyway,
and to my surprise the thing immediately turned around and made a bee line
towards the flashlight.  As I swung the light away, it continued to follow
the lens.  After I turned and pointed the light towards my shirt, the moth
landed right on my arm, giving me a wonderful look at Ceratomia undulosa.
Granted, the flashlight acts more like a point source of light and is
designed to focus the light energy into a beam, but the moth made no
spiraling motion at all.  Furthermore, my light beam was no match for the
wide spreading light from within the porch, and yet the moth did not
hesitate to leave the screen.

This whole issue is a fascinating one, and deserves more studying.  Why the
light tended to repel the moth from the inside, and attract the moth from
the outside is bizarre.

Mark Walker.
Castleton, VT