Hi borednerd-ga! (What a great name! Most of us could probably adopt
similar names!)
This is such a simple question, and yet I’m doubtful most of us had
ever given it much thought before. It just seemed so interesting I
couldn’t resist answering so here goes. . . .
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A Word about Insect Behavior
From http://www.howstuffworks.com/question675.htm
It is first important to understand one aspect of insect behavior and
that is the principle of phototaxis. This refers to a creature’s
movement tendencies in response to a light source. Cockroaches are
negatively phototactic (i.e., run from light) and moths are positively
phototactic (i.e., float seemingly out of control towards the light,
unable to break free from its virtual magnetic pull). This is a
characteristic witnessed in most species of moths and there isn’t a
definitive answer as to why that is, but there are a few theories.
It is thought that migratory species of moths use relative intensities
of light to aid in navigation. The ground is relatively dark, and the
night sky has a number of light sources, most notably the moon, which
is probably used as a primary source. The moths can then use the
relative motion of the moon across the night sky as the earth rotates
to navigate properly. When another bright light source is presented
(e.g., your TV, porch light, flashlight, etc., etc., . . .) the moth
is confused as to how to interpret this light source and becomes
“stuck” in a flight pattern around the light. As is explained on the
above website:
“So a moth's attraction to an artificial light or to a fire could be
related to orientation, and lead to disorientation -- the moth wasn't
"expecting" to actually get to "the moon" (the light source) or to be
able to fly above it, so confusion results.”
Another posited theory is that moths flee to light as a natural
defense mechanism when startled. Flight upward (or toward a light
source) will usually be a safe path so when danger is present a moth
will naturally fly toward a bright lamp or television screen rather
than to darkness, which is usually more dangerous.
Moths also seem to stay around light no matter what the eventual
outcome (demise) may be. Humans experience some degree of night
blindness when shifting focus from a bright light source to darker
areas. We eventually recover, usually quite quickly. Well, the moth’s
light sensors which send signals from its eyes to the central sensor
(ommatidium) react much more slowly rendering it blind for a much
longer period of time. Since this represents a relative danger to the
moth it doesn’t stray far from the light.
In short (relatively, I know) moth’s do not respond to the heat given
off by a light source, which was astutely noticed by yourself
(multiple benefits to careful television viewing!). They are attracted
to light as it represents sort of a “system overload” to its
navigation system.
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Another Interesting Link
http://www.straightdope.com/classics/a890127.html
This article was not quite as well written, but did provide an
alternate theory. Scientist Henry Hsiao observed that when moths are
far away from a light source they tend to fly straight toward it, but
as they approach that same source their flight paths tend to become
more orbital. He theorizes that this is due to a Mach band, which is a
visual effect seen in all visual creatures. This Mach band is a “halo”
of darkness that seems to surround all light-emitting sources. The
moth interprets this band (usually about a foot away from the light
source) as the darkest part of the sky, hence the safest, and chooses
to orbit in this range. Eventually momentum either drives the moth
away from the light or toward it. Therefore, it is chance that
eventually determines whether the moth will actually touch the light
source.
He also disproves the heat theory noting that moths are more attracted
to UV light, which is a colder light than more “yellow” light.
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I hope this answers your question. It’s probably more information than
you bargained for, but once I got started it was hard to stop. Let me
know if you need any other information or clarification.
Boquinha-ga
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Search Terms
Moth + attraction + light
(://www.google.com/search?sourceid=navclient&ie=UTF-8&oe=UTF-8&q=moth+attraction+light) |
