Attraction to Lights

[David R. Britton]

In article <17396AD6F62 at dannii.e-eng.hull.ac.uk>,
E.D.Chesmore at E-ENG.HULL.AC.UK wrote:

> I was prompted to re-submit this when I saw Chris Raper's comments
> on running a trap:
>
> "I have trapped in South America once or twice and have always
> thoughtthat overcast (even drizzly rain) increases the catch by
> blotting out the moon, keeping air temperatures higher and diffusing
> the moth light."
>
> There seems to be very little about attraction of insects to light in the
> literature, and what there is appears to be inconclusive.  For example,
> I have 2 papers discussing light attraction of Chironomid midges
> which are contradicatory - one says intensity and not wavelength
> (colour) is the most important and the other says exactly the opposite.
>  Also, what effect does the physical size of the light source have
> (compare a lighted window with a point source), or its orientation if it
> is a fluorescent lamp?   Diffusion of the light by rain or mist
> effectively increases it's perceived size but must reduce the overall
> light output, particularly in UV.
>
> Does anyone have any thoughts, comments or know of recent work
> relating to this?
>
Dave, I think the reason why so few conclusions can be made about what
conditions control species richness and abundance in light-trapped catches
is the number of confounding effects, which you mention a few of in
relation to the actual source of the light.  In addition to these, there
are a host of enironmental effects which further muddy the waters.

There may be periodic fluctuations in the abundance of various species
which might be attracted to the light.  I was speaking to a cricket
researcher who claims to have data which shows that periodic fluctuations
in light trap catches of a cricket species occur in roughly 5 day
intervals.  The reasons for this phenomenon are obscure, but the
confounding effect on comparing light trap catches from different nights
might be substantial.

I'm sure that most light-trappers will agree that positioning of the trap
has a huge effect on the catch.  If you face an open area, or are on top
of a hill, or on a track, or above a certain altitude, the catches will
vary enormously.

In relation to weather conditions, I agree that the best nights (usually)
seem to be warm, overcast, humid nights with not too much wind.  In some
cases, a little bit of rain seems to stimulate further activity.

just a few ideas,

Dave B.

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