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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8 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

  4. Levi Fillus-Sherman says:

    I started putting together the trap and I ordered six different LED’s. I also ordered a full spectrum grow LED. Would you have any experience in using these full spectrum lights? It looks like it will work for attracting moths. Would it also be possible to use a 9V instead of a computer battery?

    • petermobbs says:

      Hi Levi,

      I am not sure what you mean by a ‘full spectrum grow LED’. Most grow-lights are designed to emit wavelengths that match the absorption spectrum of chlorophyll. Thus, they would be rich at the blue and red ends of the spectrum but short on green and yellow – plants reflect these wavelengths rather than absorb them. So, they would not be a great match to the absorption spectrum of the moth eye. However, they will of course work to some extent……

      As for will a 9V current source work; that depends on how you organize your LEDs in series/parallel and how much current they will draw.

      Sorry not to be able to be more helpful.

      All best wishes,

  5. David Hood says:

    Hi Peter, I’m keen to make a very portable LED trap to survey moths up a hill in Aberdeenshire. I’d like to leave it out overnight and would be carrying it on my back so keen not to have heavier batteries than eg 12v 12AH lead-acid. I appreciate your comments above about arranging modules of LEDs to give 360′ illumination. When I try to plan for this I quickly reach the limits of the battery capacity.
    Possible answers include reducing number of LEDS using only u/v LEDs and I wonder if you have practical evidence that the blue and green LEDs add to the effectiveness or is it still theoretical based on what is known of moth eye receptors?
    I also thought that connecting the LEDs in series and limiting the current to 500mA per LED would significantly reduce power consumption. I presume I would need a step up constant current driver but when I looked on-line the instructions for setting the current seemed complicated, none of them had a digital display like the driver you show in your photos and I presume it has to be done with a meter.
    Were you perhaps intending to use your trap with 3 or 4 modules from the mains ? If from a battery I’d be very interested to hear your thoughts about power supply and drivers.
    Thanks for your time – much appreciated !

    • petermobbs says:

      Hi David,

      Lead acid batteries are great but NiMh batteries have more than twice the weight energy density so, if the main consideration is how ‘luggable’ the setup needs to be, then you would be much better off using NiMh batteries. You can buy holders for 8 D cells (2 x 4 D cell holders) that will give you 12V at 1A for 12 to 18 hours – so, you could on each set of batteries run 12W of LED lights for that period. I think I’d try making something based on one or more such battery ‘units’ running say 4 3W LEDs in series. Since the voltage available will mean a V drop of about 3V across each LED, and the 3W LEDs require about 3.5V on average for maximum light output, each group of LEDs will (at a guess) actually run at about 9W. That is still pretty bright, and if the LEDs have a good heat sink, they will run cooler and last longer. How many such ‘units’ you run would be down to your pocket and how much you can carry!

      It is true that you could choose to use a boost converter to drive a bigger series array at a higher voltage but for simplicity it is hard to beat the direct approach above. I think there are some who would criticize the above approach because not all the LEDs will run equally brightly etc…..but I think it will be fine.

      As for what wavelength to use – it’s complicated and the subject of active research at several universities. For example, it would appear that some moth species are attracted more to shorter wavelengths than others (see abstract below). However, from everything I have read and research that I did in another life, it is very likely that most, if not all moths have similar photoreceptors. I have picked LEDs to hit the spectral peaks of these. The unknown factor is how the different classes of photoreceptor drive the optomotor behaviour that leads to light being attractive to different species, or indeed in any moth species! So, I think the best bet is the one I outlined in my blog article.

      Here is an article that may be interesting…. There are a few others. To my mind they are all very flawed because what you really want is to move everything into the lab and look at the optomotor (turning) behaviour engendered by different lights of a single wavelength and equal intensity. The way to do this would be to use tethered moths and a double spectrometer with a neutral density wedge to see if light of different wavelengths and equal intensity are more-or-less effective. I’d love to do this but my days in the lab are passed….I got old and retired! However, armed with LED lights, it is possible to do many experiments – all UV arrays v green arrays etc etc. Unfortunately, I m caught up in other things so over to you and others who want to have a go!

      All best wishes,


  6. David Hood says:

    Thanks Peter – as you say “luggability” is key so the D cells make a lot of sense. Why didn’t I think of that?

    I note you don’t mention a driver to prevent the LEDs drawing excessive current. I’m guessing that because the batteries are only capable of producing less than the LEDs’ max forward voltage then no protection is needed? ( my electronics is very dodgy – A level physics from 50 years ago !)

    I would like to try comparing u/v, blue and green LEDs alone and in combination in the garden. Probably not something of proper scientific rigour, just amateurish pottering. If I get anything interesting I’ll let you know.

    All the best,

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