How to Build a Moth Trap by Barrie Jones.

How to Build a Moth Trap by Barrie Jones.
Barrie Jones is volunteer warden at White Rocks and Leaping Stocks Nature Reserves. He has a
lifetime’s experience of moth trapping and has built many of his own moth traps. In this article, he
explains how to make your own lightweight and inexpensive moth trap and in the summer edition,
he will be sharing his experience on how to go moth trapping.
This is my experiences and method of building a Skinner type moth trap, which is based on a box
design with a centrally placed light above two Perspex slides, which angle down from the top of
the sides into a box below, to leave a slot near the bottom through which the moths pass into the
egg tray collectors.
I have used plywood in the past to make the box but after a while it tends to bow particularly at
the sides where the slides need to sit flat at the junction with the top of the side to prevent the loss
of moths from the trap, especially the micros. Plywood also tends to make the traps rather heavy
so I looked around for a rigid lightweight alterative and discovered 10mm twin-wall Polycarbonate
sheeting (the type used on conservatory roofs etc).
Because I sometimes need to move them about in the middle of the night I make them up ready
to use, I can just carry them out, place them down, plug in, switch on and start mothing, no
disassembling and re- building in the dark. Another advantage is that with them being so light
they can easily be carried back at the end of the trapping session along with their electronics box
and cable reel to a central convenient point, usually close to the car, for checking and counting
the moths, this is very handy as there is no need to switch off the lights. Obviously there is a
disadvantage in not being able to flat pack them to load into the car but I can carry five traps plus
a generator, cables, etc in a saloon car and as the generator is being pushed hard if all five traps
are running with 125 watt bulbs, which is more than enough.
1 x 2400mm x 700mm of 10mm Polycarbonate sheet, which is more than enough for one trap but not enough
for two. But if two sheets are bought there is enough for three traps with very little waste.
2 x 2mtr lengths of 25mm x 25mm white plastic angle for fixing the base to the sides and ends and the sides
and ends to each other.
1 x 2mtr. length of 10mm white channel, this is used as a top surround to the sides and ends to ensure the
close fitting of the Styrene slides as well as giving even more rigidity.
1 x 4ft. x 2ft. sheet of 2mm clear Styrene sheet which is used for the slides, the two bottom retainers and a
removable rain guard.
1ltr. of white multi-surface primer paint and 1 ltr of black floor paint.
1 tube of good adhesive (I use seriously strong)
36 x 3/8 self-tapping flat head screws.
600mm. of 75mm x 25mm. planed timber.
1mt. of ¾ in wooden dowel.
400mm x 100mm x 75mm planed timber.
2mtrs. of 0.75mm white cable.
1 x 27mm. ES porcelain lampholder.
1 x allweather 3pin plug. + 6 cable fixing pins.
Note: Total cost of materials was £110
How to Build Your Trap:
1. Mark out the sizes of the sides, ends and base on the polycarbonate sheet using a felt tip pen.
See Fig A. (Note: Do not remove the protective covering on the sheet until after cutting).
2. Accurately cut out the pieces using a fine toothed handsaw or jigsaw or use a small angle
grinder with a fine diamond wheel. It is important that you keep to the marked lines.
3. Now remove the protective covering from the polycarbonate sheet and paint both sides of all
pieces with the white multi-surface primer, allow to dry and give another coat.
4. When dry, paint one side of the sides and ends and both sides of the base with the black floor
paint. (Note: They may need a second coat later).
5. Cut the white plastic angle beads and glue and screw to the base. Mitre the angle bead on the
underside of the base
6. Cut the 400mm x 100mm x75mm planed timber into four pieces to make two finished pieces
as in fig. B and two more as in fig C.
7. Undercoat the finished parts and then paint them black. When these are dry fasten them to
the black sides of the end pieces as in fig D using glue and two screws in each one from the
white side. It is advisable to drill holes for the screws and only use thin screws to avoid
splitting the wood.
8. Next position one of the side pieces onto the base inside the angle bead and mark the top of
the bead onto the white side, then cut 25mm off the white channel and press down on to the
top of the side piece at the same end as the previous bottom mark, draw a line under the
bottom of the channel, the distance between the two lines is the length of the corner plastic
9. Cut the four plastic angles to length and screw and glue to the white side of each side using
the small piece of channel pressed down on the top as a guide for the correct positioning.
10. Having done this then join the sides to the ends using the same method. At this stage run a
small bead of glue up the inside of each internal angle, place on a flat surface, measure
across corners to ensure it is square and then leave to dry before fixing to the base again
using screws and glue.
11. Fix the channel all around the top using a little glue. Measure from the inside of the shoulder
of the bottom slide holder to the top of the side and add two inches, this is the width of the
Styrene slides, the length is measured from inside the channels less 3mm. two pieces of
Styrene need to be cut to these sizes.(the Styrene is easy to cut using a Stanley knife with a
sharp blade and scoring a few times and then snapping off)
12. Two more strips of Styrene approx. 50mm wide and the inside length of the trap are needed
to act both as moth retaining baffles and also to give support to the slides at the bottom.
Another piece 12” x 12” will act as a rain guard when glued and screwed to two 12” long
dowels, the bottom of the dowels fit into 2 holes drilled into the batten that carries the
13. A strip of wood 12mm square is fastened directly under the slides on the inside of the ends of
the trap to give support to the slides at the ends.
14. The lampholder batten is drilled at each end and then screwed down into the wooden bearers.
This then doubles up as a carrying handle for the trap.
15. If the trap is being run using a 125 watt mercury vapour bulb ballast is required, ready made
up ballast sets can be purchased for this purpose or you can make your own. If you use a 160
watt blended mercury vapour bulb the ballast sets are not needed.
This may seem complicated at first but anyone wishing to see the finished trap is welcome to view
the recently built one that Barrie has generously made at the Trust HQ, on which this article is
Figure A Figure B Figure C View of position of figure B and C Finished Trap Wiring Details for Ballast