Why Do Moths Fly to Light?

Kenelm Philip fnkwp at aurora.alaska.edu
Mon Jul 28 05:15:19 EDT 1997


	Liz Day made the intriguing comment:

>...I am more convinced by the suggestion of a (much more knowledgeable      
>than I) friend who thinks moths hear the light rather than see it...

This should be easy enough to test--just cover the lamp! However, from the
following considerations I suspect such a test would give negative results
for sound attraction:

1: Tympanal organs in moths (which do have the capability to sense the
direction to a sound source) are sensitive to higher audio frequencies
(like bat sonar) and have little or no response below 500 Hz.

2: Typical moth reaction to sound detection by their tympanal organs is
to fly away from the source (weak sounds) or go into evasive action
behavior (strong sounds).

3: Organs capable of detecting low-frequency sound (hairs, antennae) do
not seem to have directional capability.

4: The sound produced by a fluorescent lamp is mainly from the ballast,
not from the bulb. I can verify this, having built a 5-lamp light table
with the ballasts a considerable distance from the lamps. The lamps are
essentially noiseless in use. In many moth traps, an insect homing in to
to the ballast would not intercept the vanes and be captured.

	(There is always the possibility that Liz' friend was making a
reference to Callahan's idea that moths detect IR with their antennae
rather than reacting to visible light seen by their eyes. That is a whole
n'other bucket of worms, which has come up on Leps-L in the past.)

							Ken Philip
fnkwp at aurora.alaska.edu




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