Moths - Build your own Trap & start catching!

Over the years I have indulged in a little hobby that may seem a bit weird, a bit geeky, to some, but it is nature-based and the results contribute to the scientific knowledge of our natural world, so I feel it is well worth doing. That hobby is ‘Moth Trapping’! The capture of moths on a nightly basis in a trap and then the identification, counting and logging of the catch before release of all the moths. A whole community of trappers do this across the country and most, like me, submit their data to the County Moth Recorder who adds them to the database for the county and this data is then available for analysis by whoever needs it. We also share our pictures, catches and experiences, helping each other too, on social media and even have communal trapping events open to the public.

I started many years ago when a birding pal showed me his trap and some of the interesting moths he was catching each night. I really fancied a go so he gave me his spare trap, complete with the required electrics. This was set up in my then Manchester home garden and my hobby started. Later on, after years of trapping, I discovered that the trap was potentially lethal, being metal, unearthed and with mains voltage running to the bulb. So I should stop using it….… yes…… well no, I gave it a few more years and then the electrics failed so an enforced lay off ensued. I subsequently moved to Cheshire and another kind friend gifted me another trap. This one was 100% safe, made of wood, portable and with low-power electrics. For the past 2 years this has served me well, the 15W Actinic (a ‘fluorescent tube’ type) Skinner Trap being in the back garden and run nearly every night to monitor the moths flying in my Northwich garden month-by-month. This trap was out in all weathers and unfortunately the walls of the trap started to deteriorate badly with the rain soaking into the edges of the untreated plywood. It was clear that a replacement was required and so’ Project Moth Trap’ began!!

I decided, given how much I loved this hobby and how I could see myself continuing with it ‘forever’ that I had better make a trap that would stand up to everything that the UK weather could throw at it and hopefully never need replacing. The electrics were still sound so I needed to create a trap built around them, to similar dimensions of the one that I was replacing. I measured up the old trap and then started my build, trying to use recycled materials as much as possible, both to keep costs down and to make it a ‘green’ project. The dimensions and specifications will be at the end of this article so if anyone wants to follow suit then the plans are there and can be followed pretty easily! Interspersed within this write up are pictures of moths caught in 2022, both in my old trap and in my new one, just to show the variety and beauty of moths seen in my corner of the NW of England.

The first stage was to sort out the walls of the trap. I had a good amount of wood in my garage from our old kitchen counters, saved when the kitchen was replaced a good 15 years ago and which my wife said I was daft keeping (“just in case”) as she reckoned that I’d never use them! This consisted of laminated chipboard in large sections around 2cm thick, good solid wood. These were cut into sections to produce an inner space the same in linear measurement around the edges to my old trap but with a bit more height to give more space. The old trap had no base so this first design mirrored that and just the four sides were cut. A couple of recesses were cut, in two opposite sides, to accommodate the bulb fitment at a later stage. Next several coats of an exterior off-white paint were applied, especially to all cut edges as a start to waterproofing the chipboard. The laminated surfaces were ideal, starting with inbuilt waterproofing anyway. All paint used in the project was leftover as was my next layer, continuing the recycling theme. I had some tasteful dark green exterior paint and so applied several coats of that to the outside surfaces and open edges only. This left the internal colour still white, hopefully this would help to attract moths to the inside of the trap when the bulb was lit and reflecting off this surface. This was a slow process given that I applied at least 4 coats of each type of paint and had to let each dry completely. My final waterproofing trick would come later after assembly of the trap. Once this was all dry I drilled my guide holes and screwed it securely together with 50mm brass screws, 3 along each edge to make a very rigid outer box construction. I had initially thought that I needed internal bracing but now it was screwed together it wasn’t moving a fraction of a millimetre!

Now I changed my plan for the completed trap after a conversation with a fellow moth trapper who had built his trap and put a base on it. The reason for no base was so that rain could not build up in the bottom of the trap and drown the moths. But his design had a fine mesh panel built into the base to allow the water out and keep the insides dry, which sounded like a plan! He kindly gave me a section of mesh that he had left over and I started to construct the base. This would have to be in two outer panels with the mesh forming a central third panel. The perspex sheets which act as vanes to channel moths into the trap would also channel the rainwater down and through the mesh out of the trap. The outer panels were cut from thinner MDF and then given the paint treatment similar to the walls of the trap, namely several coats of each of the white and the green exterior paints. With the end result being two panels with a white inner surface and a green outer one. These were then screwed onto the base of the trap. Next the mesh was cut to size and screwed into the side walls of the trap to take up the space between the two MDF base panels. Since it was impossible to get the mesh to lay tight to the floor, two batons were cut, painted with several coats of the white paint and screwed down to clamp the mesh tightly in place, thus completing the base of the trap.

Now that the outer trap box was in effect finished I had a final hack to make it completely waterproof forever. That was to varnish it, and what better product than yacht varnish, I reckoned that a few coats of that and the elements would be beaten. A few coats later I was happy, the box was fully waterproof. Next to the runners for the perspex baffles that guide the moths down into the trap and then keep them there. I had found some lengths of plastic trunking, used for hiding cables in houses, that looked perfect. So I cut those to length, angle cut the top end and then screwed them at a suitable angle inside the trap. I made sure that they were either side of the previously cut recesses so that they were in the correct place when the bulb was finally in place. Next, how to stop the perspex just sliding right down. I needed a couple of stop blocks, which were cut, painted and then screwed into place inside the trap. Finally 6 small rubber feet were added to lift the trap up by a tad to allow any water to drain away rather than the trap sit in a pool.

The trap was left for a short while to allow it to dry fully and then a few final tweaks prior to setting it up. The first idea was to build a raised plinth so that the trap was slightly higher than before. The idea was that an elevated position would make it more visible and therefore ‘pull’ in the moths more easily. A section of board was cut and painted in the same way as the trap, finishing with yacht varnish. A base for the plinth was built from old paving slabs, sections of wall and spare bricks. The design was to leave lots of gaps and nooks and crannies for wildlife to utilise in this base. The top board was then placed on top and the trap put on top of that. The bulb fitment was placed snugly into the recesses cut for this purpose and the trap was complete and in place ready for use. It had taken several months of precise work to get it right but now I was ready to switch from the old trap to the new one.

The only thing bugging me was the perspex sheets. They had come with the trap donated to me by my mate and were 2mm thick so slightly bendy. In their use over the years I had dropped one and it had broken a large semicircle of perspex out of it. This was mended using clear plastic and epoxy resin but it now didn’t match the new trap, looking a tad tatty! I decided that given the trap had cost next to nothing, having been made of recycled wood and paint I could splash out on some better sheets. After a bit of research on the web I decided on 4mm thick polycarbonate, advertised as unbreakable, that sounded perfect. I ordered two ready cut sheets and a week later they turned up and were perfect. The snug fit and no-bend (due to 4mm thickness) was better than the originals and they were so see-through it was as if they weren’t there. The previous panels had yellowed with age but this polycarbonate was advertised as non-yellowing, so we’ll see.

Moth traps are all set up to work in a similar fashion. A light draws in the moths and the vanes (my polycarbonate sheets) deflect the moths down inside the trap. To keep the moths inside the trap we put in egg boxes for the moths to roost on. Ideal are the large square trays that hold 20 eggs. These are cut in half and I fit 6, 3 each side, into my trap, with space for moths to move in between them. This allows you to remove them one by one in the morning to examine and log your catch. I had some new egg trays so I discarded my tatty old ones (into my recycling bin!). Each new tray was cut in half and then placed in situ before my first nights trapping.

The trap really was now finally ready to take over from my trusty old one. So I excitedly (sad aren’t I?!!) put my new creation onto the base and as dusk fell that evening the great switch on occurred. Not quite the razamatazz of the Blackpool Illuminations but a big day for me! That night and most subsequent nights the catch has been good. The trap has worked as planned, the polycarbonate sheets funnelling the water down and out through the mesh leaving a dry trap even in very rainy weather. One tiny improvement was to put two concrete batons on the baseboard that the trap sits on and so raise the trap up higher. This helped stop any moths getting trapped under the base of the trap and may give a better range that the light can be seen from, being higher up. One the first wet night, before raising it up, a thin layer of water had gathered under the trap and a few micromoths that managed to get underneath had perished. Since raising the trap up higher no moths have died and no water gathers underneath the trap either, so a win-win!

The trap has now been in use for several weeks and lots of moths have been caught, identified and released. Several new species for the year and even some new species that I had never ever caught before have been found. I can’t put this down to the new trap but with the old one falling apart and me not knowing how many more months I’d get out of it, I can now forge ahead trapping with confidence,

The plans for the trap are shown in a few diagrams. Any wood could be used and all the runners etc could be customised to suit. The base and mesh was an addition and it could be left with no base on, like my old trap. However the egg boxes would then sit on whatever the trap is sat on and the chance of soggy traps is higher!! Having used both I would recommend making the extra effort to add a base with a mesh centre to drain the trap. I would also recommend (so far) getting 4mm thick polycarbonate skeets/vanes for the trap. These are sturdy and hopefully longer lasting so the cost will be worth it in the long run.

As well as the detailed plans (below) several pictures are attached of moths that I have trapped as I said earlier. Given the number of species in the UK (c.2,500) then a fantastic variety can be expected. One moth trapper described it to me as opening a christmas present every morning, you never know what is inside and when you open it up you are almost always delighted with what you’ve got!

The diagrams below show the dimensions of my particular trap but the general design could be followed with different dimensions according to the materials available. The polycarbonate sheets were ordered pre-cut to 44.5cm x 33cm which gave a snug fit to the trap when placed on the internal plastic slider rail. The most problematical element to source may be the electrics but if you could find some external UV Tube fitments and a power source that will run from the mains and may have to be ‘choked’ down to a lower voltage then this would work. Alternatively it may be worth talking to one of the ecological equipment suppliers to see what they can offer. Good luck with your trap-building and I hope that you enjoy trapping as much as I do. I am happy for any enquiries through Focalpoint Optics (01925730399) and will try to help if at all possible!

Moths - Build your own trap & start catching

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