Why Do Moths Fly to Light?

[David R. Britton]

In article <19970715152015.17175.qmail at iquest7.iquest.net>,
lday at iquest.net wrote:

> A moth friend tells me that moths also fly to microwave-emitting things
> or radio towers or similar, that the moon and stars idea of navigation
> is wrong because moths are most active on damp cloudy nights with no moon.

The problem with this, is how do you know how many moths are flying?  Is
it because you have used a light trap?  No moon etc. means that there are
fewer light sources around, and the light trap is even more attractive
than usual which means that you might be observing an artefact rather than
a real abundance of moths.  It is the old problem of the observered
changing the nature of the observed.

It is further complicated by hill-topping behaviours (as seen in diurnal
lepidopterans), and by stratification in flight behavior, with some
species flying at ground level, some above the thermocline.  Position is
always important (as your friend has observed with radio towers); you will
catch more in a light trap at the top of a hill than at the bottom.  It
may also be that cloudy nights are also the ones where the temperature,
humidity and wind velocity are different to clear nights, so that there is
more activity of moths.  You are dealing with a multitude of factors, not
just the light attraction thing.  There are plenty of species which don't
even fly to artificial light, even though they are equipped with large
eyes.
>
> He says no one really has a convincing explanation for why light attracts
> them and that it would be a good research project, as if anyone would
> ever have money for that, sigh.
>
Still can't see why navigation is not convincing.  BTW, when I say
navigation, I don't mean flying from point A to point B or anything that
sophisticated.  I mean maintaining a single direction (rather than flying
around in circles), or maintaining ground/air speed, or flying in a clear
area rather than through dense bush.

> Liz Day
> LDAY at iquest.net
> Indianapolis, Indiana, central USA, 40 N latitude, zone 5.
> http://www.iquest.net/~lday

Dave B.

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