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The Society for the study of flies (Diptera)

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#1 2014-11-24 12:49:41

RobWolton
Committee
Name: Rob Wolton
Registered: 2009-08-13
Posts: 114

Malaise trap colour

I would be grateful for advice on the better colour for Malaise trap netting, black or white?  Or a combination? 

This year I bought a trap in the spring, with a white roof but black ends and central partition.  I put it out on site in early April, on a woodland edge, in a damp place but one that receives full sun for most of each day (on the infrequent occasions when it is sunny here in wet Devon).  By October, the white netting was in tatters and very easy to tear, while the black netting remained strong.  The manufacturers said that they have received previous such feedback, that in certain locations, white netting degrades rapidly.

If I use an all black netting trap is my overall catch likely to be different?  Perhaps some families are more attracted to white than black, or vice versa? Or others avoid white.....

This year I noted that male sarcophagids were using the white top of the trap as a resting place, and my catches of this family were good.  But this may have more a function of the position of the trap, at a high spot, rather than its colour.

Regards

Rob

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#2 2014-11-24 13:35:49

malcolmsmart
Committee
Name: Malcolm Smart
From: Wolverhampton
Registered: 2008-02-26
Posts: 395

Re: Malaise trap colour

When I use my hand net (white material) for sweeping, generally grab the end of the bag and allow the frame to fall/hang below. The flies in it almost invariably fly up towards the brightest light and towards the sun when shining. I the insert my pooter and collect them from the highest point (the end of the bag). The brightest light attracts (most of) them upwards.

My malaise trap has white roof and black end/centre panels, but it appears that the vast majority of flies hitting the centre panel immediately which they don't see) immediately fly upwards towards the light represented by the white roof or the sun shining through it. They then migrate upwards along the sloping ridge to the capture pot.

I believe that the reason they behave in this way is because they are attracted towards the strongest light which is generally towards the sky. A black net roof will simply reduce the light visible  above and encourage them to fly out of the malaise trap sideways. A white roof illuminated by the sun will appear as a source of bright light encourage them migrate upwards rather than sideways and hence to become trapped rather than escape.

The argument above will probably not apply to groups such as fungus gnats which seem to prefer dank/dark habitat!

Regards,
Malcolm

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#3 2014-11-25 01:15:44

Tony Irwin
DF Members
Name: Tony Irwin
From: Norwich
Registered: 2008-03-01
Posts: 830

Re: Malaise trap colour

I agree with Malcolm that a white roof is likely to render the best catch, but black roofs are regularly used - e.g. https://www.facebook.com/photo.php?fbid … mp;theater. There are advantages to all black traps as well as their durability - they are less easily seen by members of the public - possibly not a problem in idyllic Devon woodland, but certainly an issue on the Norfolk coast, where I've had two sets of guy pegs stolen this summer!

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#4 2014-11-29 01:21:28

RobWolton
Committee
Name: Rob Wolton
Registered: 2009-08-13
Posts: 114

Re: Malaise trap colour

Many thanks, Malcolm and Tony, for your helpful comments.  I shall try an all black one - could always put a bit of white sheeting over the ridge I suppose...  I guess that someone somewhere must have done some comparative work, otherwise would be a nice project!  Best wishes, Rob

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