More on building a better moth trap

My apologies for the long interval between my last post and this one. I have been battling with a 300 year old French farmhouse and its needs. I was motivated to make this post by the extensive interest in the article I wrote about constructing a better moth trap using LEDs. In particular, two kind emails from Eric Gendle made me think that it was worth encouraging people to persevere with the notion that LEDs are the way to go with respect to moth trapping. Indeed, given that manufacturers have stopped, or are likely to stop, making mercury vapour and other light sources that used to be used in moth traps, it may be the only way to go! The design I published within these pages some months ago has worked quite well for me though I have modified it somewhat, adding an ice white 3W LED to the blue, green and UV ones. The Ice White LED is an experiment – it is rich in blue light but will add to the overall spectrum throughout the visible range. We will see if it increases the traps appeal to moths! It is also the case that the new generation of UV LEDs are somewhat brighter than the one I used before, and I have used one of these in the new lamp. Coincidentally, both Eric and I have used Future Eden as our supplier of choice for LEDs and we both want to say what a superb company it is; high quality LEDs sent quickly and cheaply and, most important, Mickey, the owner has been very helpful to both of us. You can find Future Eden’s shop on Ebay or here:

First, I think it would be encouraging to show one of the pictures Eric kindly sent me. They indicate that for a very modest outlay, it is possible to do as well, or perhaps even better than much more expensive commercial designs. Eric’s trap consist of three LED light bars and a netting tent with an entry funnel at the top. In the picture shown here, there is a Skinner trap below that has also snared some moths. His system is run from a 12V lead acid battery and incorporates the resistors necessary to limit the current through the LEDs. His trap cost about £15 for the LEDs and resistors, and £20 for a 12amp hour 12v Lead acid battery with which he can run the trap for a whole night. He notes that running his trap in late autumn he attracted “100+ of the epirrita complex of late autumn moths plus 10+ each of Feathered Thorn, December and Mottled Umber and a single Satellite “.

Moth trap 1_11 copy

Now, just a quick note on the latest version of the lamp that I mentioned above. It has four 3W LEDs – blue, green, UV and Ice White. These could be run in series from a car battery without any resistors though, I have not tested this (beware!). However, I have run them in parallel configuration from a Chinese constant current/voltage supply like the one described in my original post. When run from that device, I limit the current to 3 amps at 3.5V (10.5W). I have mounted the LEDs on an aluminium bar and drilled it such that using aluminium right angle the bars can be connected together back-to-back in a V formation or four bars combined in a square configuration. To power the V one would need two constant current/voltage drivers capable of handling at least 5A, or four for the square arrangement. The advantage of a modular configuration is that LEDs are quite directional (usually spreading light within a 120 degree cone) and using more than one allows one to attract moths from a greater area. Unfortunately, I have not had time to build and test several modules run together in a trap. Future Eden can supply better quality drivers than those I have used, to power any arrangement of LEDs.

Here is picture of the new lamp (under test at low current – fiercely bright at 3A!). The aluminium bar (250 x 50 x 8mm) is only just adequate in terms of cooling if the LEDs are run at full power but it is possible, using the constant current driver, to limit the current so that the bar never gets too hot. Obviously, if one does this, one loses some light. A better heat sink would be finned and offer a larger cooling surface but the one shown is adequate particularly given it is cooler at night.


More recently, Eric has sent me some further details of his trap and the pictures below show it more detail. He says, “The (picture of the) bare frame shows the structure made from 2 of the large polythene buckets usually filled with building plaster, joined top to top and with the sides cut out.”  “The second image shows the lighting arrangement.” I think Eric’s design is very innovative and with a 4 X 3 arrangement of 3W LEDs it is going to generate a lot of light!

DSC_6298 copy

DSC_6299 copy

Finally, here is a picture of 2 of 3 (or the same one 3 times!) Giant peacock Moths that visited the original light and settled on my foot. Another fluttered around the light reflected from my shorts! These chaps are huge! Plenty of other moths were attracted too but on the days the Peacock moths visited, the main visitors were hundred of beetles!



So, the bottom line is that you definitely can make a very effective LED moth trap for a very attractive price though, you do need to be prepared to experiment a bit. Always bear in mind that there are good and bad moth days, and that on a bad day it is possible to catch very little or nothing!

Again, many thanks to Eric Gendle for sharing his experiences, pictures and design. Thank you to Mickey of Future Eden for the help he gave both of us.



About petermobbs

Inveterate meddler.
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3 Responses to More on building a better moth trap

  1. Eric Gendle says:

    Hi Peter, Thanks for your comments about my moth trap. I would say that I now always try to seal the trap. Trying to capture a moth inside the trap is very difficult and inevitably causes all of the other moths inside to take flight. Keep them all on the outside!. I do have a lid which I can open to get rid of dead flies etc, but for trapping I keep it shut tight.
    I have also made a simple hanging trap which collapses to almost nothing. It is simply a top and bottom disc as per my illustrated trap with the usual fine mesh surround without any internal supports, hence it collapses almost flat. A hook on the top for hanging from a branch and an optional small Skinner trap attached below
    Best Wishes

  2. petermobbs says:

    Brilliant Eric! Great traps and so good to be able to pack one of them away and carry it into the field and power it from a battery! All best wishes, Peter.

  3. Eric Gendle says:

    Hi Peter, a minor comment. The image showing the Leds, looking vertically into the trap was taken some time ago. The bottom is now sealed to keep all moths outside of the trap as in my previous comment

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