Attracting moths with a blacklight: Bulb or torch?

Hi all – I know there have been long discussions about attracting moths here in the forum already, but I’m still unsure what to buy. I don’t necessarily want to attract large numbers, but I am interested in maximising species diversity. I am not that much into assembling stuff, especially when it comes to electronics; I’m looking for something very easy, and relatively cheap. I don’t want to catch things but directly photograph them as they settle down. So far I did some tests with equipment I had already available (a LED floodlight directed at a somewhat reflective white plastic mat I suspended vertically on a tree) with some success at just 6° C (e.g., https://www.inaturalist.org/observations/35992787). However I still saw moths flying by that remained completely uninterested. I thought I could have more success with a blacklight in addition to the normal floodlight.

  • Would you buy a UV bulb (7 W) or a stronger torch (~100 LEDs)? I imagine that a bulb is more powerful and shines in more directions. A torch would be portable though.
  • Are you wearing UV protection glasses? I can imagine that with a bulb it is more difficult not to look into the light compared to a torch. I assume that a weaker torch (less LEDs) would drastically reduce success?
  • Is a slightly reflective white plastic sheet effective or should I use cotton instead? Could the reflective surface be a problem for the eyes in combination with the UV light?
    Thanks for any advice!

I’m no insect trapping expert, but here are some discussion about the type of light for insect trapping, which you may find it useful: https://www.researchgate.net/post/What_is_the_most_effective_light_source_to_attract_wide_range_of_insects_to_light_traps
https://www.researchgate.net/post/Which_is_a_suitable_bulb_to_trap_insects

Also to answer some of the question (again, not an expert), but UV and blue-ish light are generally recommended for insect trapping and attracting (hence why bug zappers and such have a blue light). You probably won’t need UV protection glasses, since an average human will get their most UV exposure from the Sun anyways (but…doesn’t hurt to get them, if you want to). I think the sheet should be penetrable by light, but your light should probably light up the entire sheet, just in case you missed those “edge” moths.

Hope this helps, good luck with your set up! :)

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If you want to maximize species diversity, you should just focus on attracting as many moths as possible. The more you attract, the more neat species you’ll see. It’s also possible that different species are attracted to different types of light, so having multiple lights could prove useful, but the most important factor for attracting moths is brightness. Even a non-UV light will attract more moths than a UV one if it’s significantly brighter.

It’s probably a good idea to use a cotton sheet rather than a plastic sheet for the simple reason that moths will cling to the cotton more readily. You’ll get some moths clinging to a plastic sheet, but you’ll also get a lot that just crash into the sheet a few times then end up flying away from the light so you lose them.

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Thanks for the insights, very helpful to know this. I will get the brightest blacklight torch I can find then (a torch for the simple reason that it is easily portable).

I just had some great success (just with the normal floodlight, which is quite bright actually), I am flabbergasted how many moths are on the wing even this time of the year! It seems that the most important factor for moths in winter is temperature (today it is a bit warmer). Thank you again!

A time ago I put a led lantern next to a white plastic drum water container and the effect was very interesting, attracting a lot of moths, I’m amateur of course, but it worked to me

Also keep in mind that not all species fly at the same time of night, so in order to maximize species diversity you need to be ready to sample at all hours.

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Good point, thanks!

I have an inexpensive USB black light (it’s marketed as a “DJ light”) that can either be plugged into an outlet with a USB plug or into a portable USB battery back up. I use it with a slightly textured white plastic shower curtain. All credit for this set up goes to @damontighe who came up with it and wrote a journal post about it: https://www.inaturalist.org/posts/11836-diy-moth-light

I don’t do tons of mothing but it’s been a great casual set up for me. Most of my mothing happens while traveling as my attempts to attract moths in my yard in Washington DC have been pretty pathetic. Easy to fly with, but your bag will probably get extra scrutiny from security.

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