moths & light

Kenelm Philip fnkwp at
Sun May 14 18:56:09 EDT 2000

	Jim Mason asked:

> What is the current best guess why moths are attracted to light?
> Why are insects attracted to light?
> Or is it some light (wavelengths) and not all?

	The 'textbook' answer is that many nocturnal insects navigate by
maintaining a constant flight direction with respect to celestial light
sources (so-called menotaxis). This mechanism will lead to a logarithmic
spiral in to a nearby light source.

	There are a number of other ways that insects orient themselves
to light, so the picture is no doubt more complex than that. There have
also been a number of other mechanisms proposed at various times, some
of which (as Callahan's ideas about IR and moth antennae) have not to my
knowledge ever been experimentally tested (possibly because they were
considered too wild to be worth testing?).

	Insect eyes are in general more sensitive to UV than human eyes
are, and UV lamps do very well at attracting insects. Some insects have
essentially no sensitivity to red, and would presumably not respond to
a red light source.

	Anyone who has run a light trap for moths can verify that other
orders of insects are also attracted to light!

							Ken Philip
fnkwp at

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