Thursday, 4 June 2020

Deluxe moth trap design

There's been a huge growth in interest in moths in Ontario over the last several years...the new Peterson Field Guide to Moths of Northeastern North America (by Ontario's David Beadle and Seabrooke Leckie!!) is certainly a huge factor in that. But there are lots of other important factors, too: there's excellent photo recognition now on iNaturalist (where a lot of Ontario moth-ers are reporting their sightings), the Toronto Entomologists' Association has their moth atlas (and associated Moth's of Ontario iNaturalist project) and of course there are excellent online resources for ID, in the form of Moth Photographers Group and Bug Guide.

You can just leave a light on outside your house or go one step further and buy a specialized bulb and/or set up a white sheet. Or you can build a trap. There are many designs out there and they all are basically a big container with a light source over a funnel. The most effective live trap I have seen is the one that Mary Gartshore and Peter Carson use. I'm not sure if they came up with the design or not (might have come from Mike King and/or David Beadle), but they shared the details with me so I could make my own...and I'm going to share that with you here.

The whole trap costs about $50-100 depending on how/where you get your supplies. Plus you'll need cords and a bulb.

~18 gallon "Muck Bucket" - this is the base for the trap. They're sold mostly at hardware and feed stores. I got mine at a local agriculture supply store for about $25. Grainger Canada has them righ tnow for $18 online here.
18 gallon muck bucket
12 inch funnel. These are surprisingly hard to find. Phone around to brew your own beer or make your own wine stores. I ended up getting them at a wine store for about $10. These funnels are perfect because they're designed to sit over the mouth of a large bucket, so they have a small lip around the top edge.
12 inch funnel
Plexiglass. This is for the fins. You'll need two pieces that are about 11 x 11 inches each. I used 1/8 inch thick but 1/4 inch is recommended. I actually snapped my first piece the extra width will give you more strength especially as you weaken it with cutting. You can buy sheets at hardware stores and online on Amazon but you might be able to go to a local hardware store and ask if they have any scrap pieces big enough for you - that would be much cheaper (maybe even free).

Glass bowl. This is the rain cover and is optional if you don't plan on leaving your trap out in the rain ever, but I'd recommend it. Mary and Peter use a Pyrex #322 1 quart mixing bowl. I found something similar on Amazon for $5.

Light socket/cord. You can get this at any hardware store for a few bucks. The best is if you can find one with the cord/attachments coming off the side or off the bottom not perfectly in the centre because ideally you'll have it sitting flush along the bottom. I couldn't get in to a hardware store at the time so ordered this one from Amazon for $12. You can get the same thing off Amazon for much cheaper if you are going to order a few at a time. I was able to make this one work pretty well by unscrewing the plastic cover at the very bottom of the socket, giving a bit of flex to the cord right at the base. It wasn't perfect, but good enough.

Corrugated plastic: this is for the "lid" of the trap. The easiest thing is to find an old election sign but if you can't find one you can order them online from lots of places or you can check your local hardware and craft stores. You'll need a piece that's about 2 x 2 feet. (If you're local I have some extra sheets I could give you)
sheet of corrugated plastic
Margarine container and screen. This is for the drain and again could be omitted but is a good idea to include. I used some scrap window screen I had on hand (again, if you're local I can give you some).

Glue gun
Something for cutting plexi-glass. I used a dremel tool with a plastic cutting wheel, but you could use any number of other tools. Theoretically you could use an exacto knife but I think you'd end up  A band saw would probably be the easiest.

1. Cut your corrugated plastic for the lid. Basically, trace the top of the muck bucket and then add ~10 cm around it and cut that circle. Then you'll want to line up the handles and cut slits for them. Finally, trace the top of your funnel on the centre of the sheet. Then follow that line about 1 cm inside to create a slightly smaller circle (the exact width should be close the width of the lip on your funnel). All of this can be cut with a sharp exacto knife. You may have to do some small adjustments to make sure the funnel fits properly. Once you're finished, the lid should look something like this:

The "lid" - sheet of corrugated plastic cut to size/shape
2. Cut the narrow part off your funnel. I used my dremel tool for this but an exacto knife would work too. You want to cut it so you leave an opening about two inches across.Mine is two inches exactly and that's big enough to catch the biggest moths we have in Ontario - I caught Cecropia, Luna and several sphinxes in the first couple nights.
Funnel with narrow neck cut off
3. Next you will make your drain. Take your margarine container and cut most of the bottom out of it. Next, cut a circle of screen to cover the bottom of the container and use the glue gun to attach it. Then, cut a hole in the centre of the bottom of the muck bucket and glue your margarine container (face down) over this hole. This should be centred properly so any water that drips down your funnel will fall onto the screen and drain down. By having the screen portion elevated you'll prevent moisture from coming back up.
Margarine container with bottom cut out

drain cover installed

Another look at the drain. There's a hole right through

4. Now it's time for the fins. Peter was good enough to provide me with his pattern on one inch grid paper:
Designs for the fins. This is one inch grid paper
It fit my funnel pretty closely, but I did have to adjust the sides a bit so it would fit fairly snugly. I also had to widen the notches in the top to fit my glass bowl (mine was slightly wider than the one they use). As I mentioned previously, I used a dremel tool to cut the pattern and then used a sanding attachment on the tool to make some fine adjustments. Especially the narrow part at the bottom (where the light socket goes) you want to be quite exact to match the width as close to perfectly as possible.
The fins are cut and sitting together in the funnel
5. Now your fins are cut, fit them together and make sure the fit snuggly in the funnel. You might have to do some back-and-forth here with sanding and fitting until they fit nicely. It's also important to check that the bowl fits on the top now (in the recessed spot created by the notches). You also need to do the same for your light socket to make sure it will fit snuggly in place. Once you're happy with how it all fits, you can glue it with the glue gun, using a bead along each line the two sheets touch.

6. Once the glue is cooled, fit your light socket in place and glue it again with copious amounts. You can then assemble everything and it should look something like this:

Close-up of the light socket glued in place

The finished product.
7. Before you run it, don't forget to fill it with egg cartons so the moths have somewhere they can hide and feel safe once they're stuck inside. Don't block the drain.
The trap all set with egg cartons
In the morning you should have a trap full of moths to look at :)

Bulb: you can use any bulb you like. Mercury Vapor bulbs (like the one pictured above) are the favourite of most moth-ers, but are getting harder and harder to find. If you've got a good lead on a place to find them, please let me know! I've got a few left from an eBay order last year.

Once last tip: if you've got a dusk til dawn outdoor timer that's a handy way to save on energy.

Again, I'd like to thanks Peter Carson and Mary Gartshore for the design of this trap - without their help I'd still be using a much less effective trap.


  1. This is exactly the kind of guide I have been looking for!

  2. Do you think a scaled-down version of this would still work? I'm thinking 7L pail instead of the muck bucket. I guess there's only one way to find out :)

    1. Ya for sure - it would work. The big muck bucket is a nice size especially for really heavy nights. You might end up with more beat up/damaged moths in a smaller container.