I am curious about others’ thoughts and perspectives on this topic. I haven’t seen too much on the internet about it. How much light-attracting is too much? If you leave a powerful light on all night for several days a week, are you significantly affecting the behavior of moths in the area, disrupting their natural mating/reproduction habits? Or is the thought that if you’re in a large ecosystem, only one bulb/trap can’t do any significant damage to a population at large? I ask myself these questions in my own practices. On the one hand, you could be in a large forest without many other lights around, but on the other hand a few miles away, you might have entire suburbs and residential neighborhoods nestled among forests which account for a billion lights potentially attracting insects away from their natural duties.
I am not an entomologist or lepidopterist, but I assume this topic has been well considered amongst folks of that ilk. I’ve read published studies where it seems like light traps are left out for consecutive days for months at a time, but I’ve seen it mentioned elsewhere that breaks are advised to give the moths a chance to do what they do. Is there an unofficial ethics code or standard acceptable practice regarding this?
I am not making suggestions or statements, only asking questions. What do you think? Do you have your own personal rules?
I usually just photograph moths and other insects that are attracted to light sources that other people have left on for unrelated reasons (usually lights for livestock barns). I’m against light pollution in general but in this case I just take advantage of lights that were going to be on anyway to get pictures.
I generally don’t use the extremely vibrant coral lights a lot of entomologists use to attract insects (again, because I only take photos opportunistically), and even if I did my gut instinct is that if I did as part of a wildlife survey I’d only use them one or two nights to avoid disturbing the local wildlife too much.
By the time moths come to lights, they have most likely already bred and layed eggs, so as long as your not disrupting the larval food plant, I dont think there’s much to worry about their. I dont think that light traps do any significant damage to over all populations. It is possible to overtrap a local population, especially with early season moths in my experience, but as long as you move the traps around, and dont keep/collect every moth you catch, I think its fine. I dont know of any official or unofficial ethics code to go by. Its safe to assume that leaving any lights on will affect the behavior of moths, but not by to much and not to every individual moth in the area. Iv seen alot of moths fly right by light traps without stopping, and other show some curiosity but not stay for more than a few minutes.
The negative effects of moth lights are negligible. If you are concerned about the ecological health of moths, please help raise awareness about the negative effects of poorly regulated insecticide use by industrial agriculture. Insect populations throughout the world are declining significantly due to this issue (although it is often talked about only in the context of bees, since those are the most economically significant insects).
yes, point well taken that compared to largescale habitat loss and other human-driven environmental factors, an individual moth light seems insignificant, thanks for your thoughts
I have never heard that by the time moths come to lights, they have most likely already bred and layed eggs, is that well established? I know I’ve found some eggs around my light set up plenty of times.
In my opinion - use light just when you need it, you don’t need it for all the dark hours each day, even as collector you probably won’t be able to do as much damage as one single window does in dense moth area, biggest threat of it is lamps themselves, moths shouldn’t be able to touch the heat, otherwise don’t see it as a really big deal, unless you have some massive construction.
No; it has been known to significantly alter copulation and oviposition patterns. https://onlinelibrary.wiley.com/doi/full/10.1111/icad.12447
As for my own thoughts on light trapping: although I am aware that individual bulbs have a relatively low impact on the population as a whole (especially in areas which already contain a lot of nighttime artificial lighting), I generally avoid deploying light traps and tend to use preexisting light sources instead.
I personally think the use of light traps to document moth biodiversity will overall be more beneficial in the long run in terms of evaluating the health of the ecosystem etc.
This seems like a case where quantity matters. Use a light for a while, even all night, but not every night. Probably not even most nights. Turn it off when you don’t need it. That will minimize impacts. Keep a bright light on all night every night and at least local populations of some species could be harmed.
Relative to the sheer number of streetlights, your light is inconsequential. You probably negatively impact (kill) many more insects with your car driving down the highway.
Something interesting and vaguely related to this discussion is that moths are capable of adapting to be less attracted to light. There was a study that found that moths reared from larvae collected in an urban area were 50% less attracted to a llight source than those from a rural area with less light pollution.
When I tried light trapping in a rather built up and light polluted area of southern Florida, I had very little luck attracting moths- even on warm nights in the darkest spot I could find to set up a light trap I would barely get any moths, even though I regularly saw large moths like sphingids and saturniids flying around in the dark and found caterpillars. I would sometimes see moths sitting on walls near lights, but not many. I imagine the moths’ adaptation against attraction to light may have been sped up by the house geckos lurking around lights on every building.
I sometimes got good numbers of junebugs and similar beetles, possibly because those beetles are less dependent on flying to complete their life cycle so the selection pressure to avoid lights is less intense?
A potential takeaway here is that not only is light trapping a drop in a bucket in areas that already suffer from light pollution, it might not even be disrupting moths that much in those areas, at the expense of being less successful. Getting good numbers of moths at light traps in areas with less light pollution could be indicative that their population hasn’t been suffering from light pollution.
To echo @coniontises and @polypody , I did some demonstrative light-trapping in a very remote, protected section of the Mt. Rogers massif in SWVA a few weeks ago. With a single, relatively low-powered light on a sheet attached to the back of my car, running off of my boss’ truck battery, moths were instantly attracted. Almost as if they were magnetized (examples, that actually need review in case any Northeastern moth-ers want to check out a disjunct, southern population of some subalpine species: https://www.inaturalist.org/observations/89425104 ; https://www.inaturalist.org/observations/89425111; https://www.inaturalist.org/observations/89425112; https://www.inaturalist.org/observations/89425109)
There is little light pollution here, and that which does exist is usually blocked out by the surrounding mountains. The moths here seemed to be entirely overwhelmed by the new light source; some of which damaging their wings rather severely as they beat themselves half to death on the sheet and surrounding windows.
Back home, still in the mountains but with much more anthropogenic light coming from the city of Bristol, I might have half the moth diversity barely seeming interested in the light. Flying by without stopping, barely lingering, instantly darting away when disturbed. It definitely is a massive disruption for the moths affected; but the question is whether it’s worth it or not. After all, a the floodlights of a nyctophobic neighbor or the unholy, sun-like glow of gas stations at midnight will probably attract more insects (coincidentally) than most backyard “moth parties.”
Forgot to add: Lots of eggs are laid at lights. And not just by moths; here we have mayflies, stoneflies, craneflies, beetles, antlions, and even nocturnal dragonflies that sometimes lay all of their eggs on dry bricks or sheets that will likely never hatch, much less mature, without intervention. It’s kind of sad, and while I’m not currently speaking from the perspective of a researcher who needs to enforce nightly light-trapping sprees, I try my best to alleviate most moth lights unless it’s a “special occasion” for scientific, interpretive, or personal reasons.
I certainly witnessed something like this when visiting a village with much less light at night and no streetlights, each window on ground level had 20-30 moths constantly and big spiders hanging around, so it’s a constant situation, but people living there are also go in bed early, so window lights are on only for a couple evening hours, while in town there’re both streetlights and lights from windows and lights near trash “places” which get some moths, but more like 1-2 at max while there’re really much more locally.
Please excuse my ignorance here, but does light trapping of moths end in their extermination? Or eventual release?
i went to a blacklighting event at a local park and they had a powerpoint about moths and stuff before we went out, and they actually touched on this!
they advise turning the lights off well before sunrise, or else the moths easily become a buffet for birds. they also advise not doing the same spot every night to give the moths in that area a break.
unless anyone collects any, no. they just are lured to a light and just sit there basking in it. its not a zapper
Although, I have seen (and described in a recently published paper) moths killed when they came to the porch light of a house that had recently been sprayed for ants and termites.
At least in my experience, the light attracts the moths, and the traps well, trap them, so participants can come and take photos/documentation etc. Then when the session is over, we turn off the lights and just shake/bang the trap and the moths fly away. Those who do not want to leave we just flick them off, which almost always encourages them to fly away.