DIY Moth Light Trap

How to build Chris's DIY moth light trap:

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All you really need to "trap" moths is a bright light, which can be projected on a light-colored building or a suspended white sheet, which attracts moths to land there where they can be viewed. Next in moth trap complexity is simply a light on top of a funnel on top of a bucket: The light attracts moths, the funnel directs them into the bucket, and the bucket retains them.

 

Here, I explain how to build a more sophisticated bucket light trap of my own design, using materials that anyone can purchase. This trap is suitable for collecting and retaining moths for research purposes. I am providing links to the products that I used for my own traps, however please note that other, cheaper alternatives are available. ​​ 

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*Nothing on this page is a paid advertisement, and I am not selling designs for traps.

**This project may require specialized tools, such as a saw able to cut metal in circles of precise diameter. Please read carefully before purchasing anything. 

***Rather than purchasing online, I recommend visiting stores to measure and test products in person. 

****The total cost of the materials for this trap is ~$390 per trap, but keep in mind that I used top-of-the-line LED lights, and optional, expensive additions for my research purposes like metal filters. With cheaper lights and no filters, a trap like this can be built for under $200. 

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1. Gather all the necessary materials. Refer to the diagram above. 

A. A light source to attract moths. This will likely be the most expensive item. There are many options for light sources, but I prefer the portability and efficiency of modern LEDs, and these ones can be easily attached to the vane in this design, and are water resistant. It is important to match the light source to your battery capacity. These LEDs are 2W, 12v and two of them can run for 12+ hours off of a 26000mAh power bank. It is also important to purchase a light with the correct wavelength of light emission. Moths are maximally attracted to light in the UV-A to violet range (~350-450nm).  While broad-spectrum lights like mercury vapor encompass this emission spectrum, narrow-spectrum LEDs must be purchased in the correct wavelength range. These LEDs are UVA and peak at 360-365nm. Cost for these two LEDs: ~$175.00

B. A vane, which helps catch and direct moths into the funnel. I use clear acrylic sheets, which can be purchased at most hardware stores and easily cut to shape with a scoring knife or utility blade. My final vane size is ~14"x11". ~$15.00

C. Optional: Foam tape, like this, which I needed to provide a tighter seal when resting the funnel on the bucket when using a vaporized killing agent like ethyl acetate. ~$2.00

D. & E. Cables to connect your battery to your lights. With the batteries and lights I use, I need a combination of a two male to one female DC splitter cable with a USB A to male DC cable. ~$5.00

F. A standard 5-gallon bucket, available at most hardware stores. This is where the moths will be collected. Color does not really matter, but I went with green so my traps were less conspicuous in natural surroundings. White buckets may increase moth attraction by reflecting more light. ~$5.00

G. A battery to power your lights. For portability I use regular phone/tablet power banks, like this one. At 26000mAh, this battery can run the two LEDs I use for over 12 hours. Note that this type of battery can not run more energy-intensive lights like fluorescent tubes. Many people use motorcycle batteries for those types of bulbs. ~$45.00

H. Nut and bolt or other fastener to secure lights to vane (depending on your light source, you may need something different). ~$1.00

I. Some type of strong wire to secure vane to funnel. Zip ties also work, but I've found wire is more durable. ~$2.75

J. A funnel. This directs and traps moths into the bucket. I have found that these white plastic funnels used by brewers work perfectly with standard 5 gallon buckets. ~$20.00

K. OPTIONAL, FOR KILL TRAPS ONLY: If you must euthanize specimens for research purposes, I've found that ½ pint paint cans with holes drilled into the ids to fit tiki torch wicks do an excellent job at wicking ethyl acetate, and two cans with two wicks each filled halfway lasts a whole night (I use two to distribute the vapors more evenly). I secure them to the inside of the bucket to elevate slightly off of the first filter with adhesive velcro strips: ~$12.00 for two units. 

L. Optional: Filters to separate moths by size. I used 14 gauge perforated aluminum sheets cut to precise diameter circles to fit tight in the traps. The diameter of the perforations is important and will determine which size moths fall to which layer. Since standard 5 gallon buckets taper a bit, the distance of separation of each filter from each other and from the bottom of the trap also determines the diameter of the circles you should cut. For my traps, the top filter has 0.375" diameter holes and was cut to a diameter of 10.375" to rest tightly when elevated 2" above the bottom filter. This filter separates large moths (like the Sphingidae) from the medium moths (like most Noctuidae). The bottom filter has 0.1875" diameter holes and was cut to a diameter of 10.25" to rest tightly when elevated 0.75" from the bottom of the trap. This filter separates out the "micro moths". ~$100.00

M. Optional, if using filters: Bolts that fit through the filter perforations and are the correct length to elevate the filters the desired height. Secured with nuts. Three per filter, spaced evenly around the diameter, provides enough balance. I used 2" bolts on the top and 0.75" on the bottom. I recommend to check fit for filter holes in person. ~$6.00

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Other tools needed: Drill, small saw or other way to cut plastic funnel, measuring tape or ruler, wrench, scoring knife or utility blade, screwdriver or other tool to punch holes in soft metal paint can lids if using killing agent, and a way to cut metal circles of precise diameter if incorporating filters.

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2. Assemble the trap. Exact assembly depends on your materials, but for this trap, I needed to: 

i. Cut/saw the bottom of the funnel so that the opening is about 2" diameter (which allows all sizes of moths in, but prevents them from escaping back out easily). 

ii. Line the top outside of the funnel with a layer of foam tape to seal tight when placed on bucket.

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iii. Cut the acrylic vane to the appropriate size using a scoring or utility knife. The width should match the inside diameter of the funnel. For this trap it's ~11". My vanes extend 8.5" above the funnel. At the bottom of the vane, I made two angled cuts matching the inside angle of the funnel, that allows the vane to extend into the funnel for another ~6". This improves moth retention and provides a place to attach the vane to the funnel. See images above.

iv. Attach the vane to the funnel. I drilled two sets of two small holes (just large enough for the wire to pass through) on opposite ends of the funnel, then two small holes on either side of the vane where it meets the funnel holes when in place. This allowed me to secure the vane to the funnel by threading wire through one funnel hole, through the vane, then back out through the other funnel hole, and twisting to tighten. See images above.

v. Attach the lights to the vane. With the lights I use, I only needed to drill one hole in the middle of the vane, then secure the lights to the vane and to each other with a nut and bolt.  See Images below.  

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vi. If using filters: Assemble the filters by cutting them to size (for my traps, exact sizing is described in Step 1 above). I had our University machine shop cut them with a rotating table saw. Exact measurements and precise circles are important to prevent moths from falling down any gaps between the filter edge and bucket wall. Attach the nuts and bolts to the edge of the filters, evenly spaced around the diameter. See images above.

vii. If using killing agent: Assemble the ethyl acetate wicking cans by punching 2 holes in each can lid large enough to just accommodate the tiki torch wicks. Wicks should be cut to ~6". Using a strip of adhesive velcro, attach one side to the cans, and the other to opposite ends of the inside of the bucket, so that the cans rest near the top of the bucket but below where the funnel inserts (and ~1" above the top filter if using filters). Ethyl acetate vapors tend to sink a bit in the trap, so putting the cans near the top will ensure that all moths are exposed. See images above. 

 

When ready to trap: 

1. If using filters, place them inside bucket.

2. If using killing agent, fill each can ~halfway with ethyl acetate, seal lids tightly, insert wicks into holes, and secure cans to velcro on inside of bucket. Ethyl acetate will start wicking immediately, and vapors usually euthanize moths within ~30 seconds of exposure (see Precautions below).

3. Place funnel/vane on top of bucket. 

4. Place bucket in desired location (See Precautions below).

5. Attach cables to light source, then to battery. I recommend placing any non-waterproof batteries in plastic bags to protect from possible rain. 

 

Now when the sun sets, moths will come! Sometimes it takes ~1hr after the sun sets for moths to start arriving. If your battery/light combo has enough power, you can set traps at sunset, and retrieve them at sunrise. Even without a killing agent, moths will settle in the trap, and you can view them carefully and often even pick them up carefully without them flying away. Or you can periodically visit the trap, removing the funnel to view the moths inside. Placing small pieces of egg carton or cardboard in traps gives moths a better place to land on and settle and can improve retention. 

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***When done viewing moths (if not using a killing agent), be sure to release them carefully in a protected area, preferably with vegetation for them to hide in***

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Precautions:

• EXERCISE EXTREME CAUTION if using ethyl acetate. It is highly flammable, highly volatile, and a skin/airway irritant. Only use outside in well-ventilated areas, avoid skin contact, and do not inhale the fumes. Keep away from any sources of flame. 

• Do not stare directly into UV light sources, and use UV protective glasses whenever possible. UV light damages eyes.

• This trap design is not waterproof. It can withstand light drizzles, but since the opening is not protected from the rain, anything more will swamp the moths inside, and ruin any research specimens. You can attach a "roof" to the top of the vane (such as a plastic pot saucer), but generally it is better not to trap (or at least be ready to retrieve them quickly) if rain is expected. 

• Secure traps in place by pushing dirt around the bottom edges of the bucket, or placing rocks around it. Traps can be knocked over in wind, especially with vanes attached.

• Make sure you have permission to trap insects at whatever location you place the traps. If you are somewhere in the range of a state or federally protected species, it may be illegal to kill or even trap insects with these types of traps. Do not place traps in public places like city parks unless you have permission from authorities.   

• Traps (particularly the battery and light components) can be targets for theft especially when placed in conspicuous locations or areas accessible to the public. The lights also make them easily located in the dark by curious or nefarious people. Ideally, only trap on your own private property or other's property where you have permission. If you are on public land like national forests (and if there are no protected nocturnal insect species in the area), it is likely legal to trap insects--but since these areas are accessible to the public, your equipment may still be messed with or stolen. Either keep a close watch on the traps or put them in a hidden area where you are confident nobody will see them. It is also a good idea to fix a label to the trap with general information about what it is, a warning not to disturb it (especially if using ethyl acetate), and your contact information especially if it is for research. I have had curious people stop to look at my traps and leave them alone when they read the label, and I have been contacted by forest service employees inquiring about them. 

• Like some humans, some animals like to mess with traps. Some mammals are attracted to the lights, and I have had wires chewed and traps knocked over (bears, raccoons, skunks, mice are all possible culprits). Just be aware of potential animal activity in your area.

 

 

A trap in use