Attraction of moths to light

Dave Chesmore E.D.Chesmore at e-eng.hull.ac.uk
Thu Jul 17 05:15:48 EDT 1997


I have read with interest the various comments about moths being 
attracted to light.  These are a few thoughts.

It is well known that most insects eyes are sensitive to UV light, 
insect killers and moth traps utilise this.  Colour also seems to be 
important to different species and coloured lights or reflective cards 
are used to attract pests.  For example, yellow or green attracts 
Chironomid midges (sewage flies) much better than white, blue or red. 
  Lights with significant UV content attract moths is much largr 
numbers than normal incandescent lights.  The sonic idea is 
interesting and deserves investigation, however, the frequency will 
depend on the type of power source.  All mains operated lamps will 
produce 100Hz (UK) or 120Hz (US) (twice mains frequency) BUT 
battery powered fluorescent lamps will produce 20-50kHz because of 
the inverter circuit. A very simple test would be to use 2 incandescent 
tungsten lamps or equal output intensity, one powered by the mains 
and the other by a battery (no sound).

A comment was made about the sensitivity of moth eyes being 
sufficient to see the light from stars.  A more pertinent question is is 
the visual acuity sufficient to actually see the stars themselves?

I operate a moth trap regularly and have seen little evidence for the 
spiral theory - most fly straight toward the light and few settle 
immediately.  Also, in the UK the moon has a considerable impact on 
moth number caught in traps - they drop dramatically.  The ideal 
night is warm, humid and cloudy!   I tend not to believe in the use of 
the moon for orientation.  I have been thinking about Ian Woiwod's 
comments about light and dark patches and feel there is something 
here.  A light appears much dimmer when the moon is out.

One question:  what effect does the size and orientation of a light 
source have on attractiveness?  Take a lighted window 2m x 2m and 
a light 4cm in diameter  - both attract insects - how?  Any thoughts?

Dr David Chesmore, FRES
Environmental Electronics Research Group
Dept. of Electronic Engineering
University of Hull, Hull, HU6 7RX
Tel: +482 465062;  Fax: +482 466664
Email:  E.D.Chesmore at E-Eng.Hull.AC.UK
Web page: http://www.hull.ac.uk/php/eepmds/home.htm


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