Why Do Moths Fly to Light?

[David R. Britton]

In article <19970714221300.SAA19823 at ladder02.news.aol.com>,
gslsdog at aol.com (GSlSdog) wrote:

> (GSlSdog) wrote:
>
> >> Why do moths fly toward the light at night?
> >> How could this behavior have evolved during the time when there were no
> >> lights at night, before humans had come along with fire and light
> bulbs?
>
> Dave B. responded:
> >errr, have you been out at night and seen those bright lights in >the
> sky.....?
>
> Hi Dave,
>
> Yes I have seen the moon and the stars, but no little green men yet (but
> then I'm  only 11 years old), if that is what you mean. Are you saying
> that moths evolved this behavior (going to light) by heading toward the
> moon and stars? Stars don't seem bright enough!

Sorry aboutthe snarky earlier reply GSISDog; the current theory(ies)
suggest that moths and other nocturnal insects) do use celestial bodies as
an aid to navigation at night.  When a moth is flying it uses the moon
(for an example) as a large object which (as far as a moth is concerned)
is a large stationary object which can be used to navigate between
points.  What a human light source does is act as a superstimulus; it is
much brighter and much closer.  Because the angle between the horizon and
the human light source is so different to a celestial body, the moth's
navigation system gets totally screwed up, and it ends up flying in
spirals around the light.  Researchers have studied the behaviour and have
noted the flight pattern, and how the spiral formed consists of a set of
angles between the moth and the light, and have deduced how this might be
occurring with natural light sources as a navigational method.

> Maybe they head toward the
> full moon each month and meet higher up, and can see each other by the
> bright moonlight so they can mate?

Many nocturnal insects use pheromones (communication chemicals dispersed
through air) to attract mates, or acoustic signals (eg. crickets) rather
than visual cues.

> Are there fewer predatory birds/animals
> out at night that might eat them? Is that why this behavior was selected
> by evolution?

That might well have been the original reason, but there are a lot of
hungry bats out there now!

>
> Also, why is it that most moths seem to disappear during the daytime?

Like you suggested earlier, moths are adapted to fly at night; during the
daytime, their specialised senses are useless, and they would be easy
targets for hungry birds.  Many species of moth have developed cryptic
wing patterns so they can sit on bark, leaves etc. during the day and not
be spotted.  They are around, but you just can't see them.

> Please be more specific with your answer, I didn't quite "get" your first
> one.
>
Hope this helps

Dave B.

--
David R. Britton, Biological Sciences, University of Wollongong
Wollongong, NSW, Australia, 2522.
Ph.(61-42) 21 3436,Fax.(61-42) 21 4135