Moth Light Trapping: How to Attract and Catch Moths at Night

Moths are attracted to ultraviolet light, and that is the whole secret of night collecting. Put a UV lamp in front of a white sheet on a warm, cloudy, moonless night, or set up a light trap, and moths will come to you instead of you chasing them. Run the light until 2 or 3 in the morning and you will see species you would never find during the day.

Night collecting is my favorite part of entomology, and it is also the most social one. You set up the light at dusk, grab a chair, maybe start a barbecue with friends, and then the show starts. Every hour brings different visitors, from small geometrids to huge hawkmoths and silk moths. This guide covers everything I use and everything I have learned doing it: the lights, the power, the sheet, the traps, the timing, and what to do with what you catch.

The short version

• Use ultraviolet light, ideally 365 to 395 nm. Ordinary white light attracts far fewer moths.
• Choose a warm, cloudy, windless night around the new moon, away from street lights. Around the full moon far fewer moths come in.
• Either collect actively at a white sheet, or let a light trap work for you overnight.
• Run the light until 2 or 3 am. Many species do not show up before midnight.
• Stay outside nature reserves and protected areas. A garden is perfect.

Where to do it: outside reserves, ideally in a garden

Rules differ from country to country, but nature reserves and other protected areas are almost always off limits for collecting, and a bright light at night counts as collecting. Set up on private land with permission, at the edge of a field, or best of all in your own garden.

A garden has one big advantage: you have a 230 V socket. No generator, no batteries, no worries about running out of power at midnight. If your garden is close to a meadow, a forest edge or a river, it can be just as good as any remote spot.

Two ways to do it: at a sheet or with a trap

There are two basic approaches, and most collectors use both.

• Active collecting at a light sheet. You hang a white sheet, light it up and stay with it. Moths land on the sheet and you pick out what you want. It is the most fun and you see everything as it happens.
• Passive collecting with a light trap. A lamp sits on top of a container, moths fly into it and stay there until morning. You go to bed and sort the catch at dawn.

The light: wavelength matters more than brightness

Moths see ultraviolet, blue and green light best. That is why the right lamp is not simply the brightest one, it is the one with the right wavelength. For collecting you want lamps that emit mostly ultraviolet, typically between 365 and 395 nm. An ordinary white household bulb attracts only a fraction of what a UV lamp does.

These are the main types collectors use:

• Mercury vapour bulbs. The classic for serious night collecting. Self-ballasted bulbs, typically 125 or 160 W with a standard E27 screw base, need no extra electronics and simply screw into a socket. They are very bright with a lot of UV, but they need 230 V and draw a lot of power. Stronger 250 and 400 W bulbs exist too, usually with a larger E40 base, and some of them need a separate ballast.
• Blacklight bulbs and tubes. UV fluorescent tubes and compact blacklight bulbs with an E27 base. Less power hungry than mercury vapour and still very effective.
• UV LED lamps. Light, low power and robust. They run from a power bank or a 12 V battery, so you can take them anywhere.
• Multi-chip LED lamps. The most professional LED lamps combine many chips with different wavelengths, usually UV with blue and green, so they cover as much of the spectrum moths see as possible. Research on the LepiLED lamp found that a lamp with mixed UV, blue and green light attracted 17 percent more moths than the same lamp with UV only.

For a light you can carry in your pocket, my Moth Attracting UV Light is a 10 W UV LED lamp that runs from any power bank over USB. It weighs almost nothing and you can connect several of them together for a bigger setup.

Power: socket, power bank, car or generator

How you power the light depends on the lamp.

• 230 V socket. The easiest option in a garden. Any mains lamp works.
• Power bank. Enough for USB LED lamps. A good power bank runs one through a whole night.
• Car with a power inverter. An inverter turns the 12 V from your car battery into 230 V, so you can run mains bulbs in the field. With LED lamps, the draw is so small that you do not need to run the engine. With discharge lamps around 100 W and more, keep the engine running, otherwise you will have a flat battery and a long walk home.
• Generator. The traditional choice for big mercury vapour lamps far from any socket. Put it as far from the sheet as the cable allows, it is noisy and smelly.

Setting up the sheet

A big white sheet does two things. It reflects and spreads the light, so the lamp is visible from much farther away, and it gives the moths a bright surface to land on, where you can easily see and catch them.

• Go big. The larger the white surface, the better.
• Hang part of it vertically and spread the rest on the ground. Many moths crawl up the sheet, others drop down in front of it, and you want to catch both.
• Hang the lamp at about half to two thirds of the sheet height, in front of the sheet.
• Think about the wind. Place the light so moths can fly in with the wind, and so the sheet itself is sheltered.
• Pick an open view. A spot at a forest edge or above a meadow, where the light can be seen from far away, beats a spot hidden among trees.

The light tower: a sheet you can pack in a bag

One setup I use more and more is a light tower. Put a UV lamp inside a white collapsible mesh cage and the whole cage glows from every side. Moths land all over the mesh, it takes a minute to set up, and it packs down flat. My UV light with a 40 x 40 x 60 cm cage is exactly this set, or you can combine the lamp with one of my mesh breeding cages.

Check the surroundings, not just the sheet

With a strong lamp, some moths never make it to the sheet. Many species settle in the grass, on bushes or on tree trunks 10 to 20 m away from the light. Every now and then, take a headlamp and walk a circle around the light. Some of the best finds of the night sit quietly in the dark at the edge of the lit area.

A net helps a lot too. Bigger moths often circle the lamp for a while before landing, and with a butterfly net you can take them out of the air gently. The technique is the same as by day, see How to Catch a Butterfly Without Hurting It.

When to go: weather, moon and the time of night

The right night

• Warm. Temperature matters more than anything else. Warm nights bring far more moths and more species.
• Cloudy. Clouds keep the night warm and block moonlight.
• Windless. Wind keeps moths down and blows the sheet around.
• Around the new moon. Always check the moon phase before you go. Around the new moon the night is dark and your lamp is the brightest thing around. Around the full moon the moonlight competes with your lamp and far fewer moths come in.
• A little drizzle is fine, as long as it stays warm. Some of the best nights are humid and overcast.
• Away from other lights. Street lights and lit buildings nearby compete with your lamp.

The time of night

Different moths fly at different hours, and that is why the night keeps changing. Hawkmoths often turn up right after dusk, while many other groups come much later, some only around midnight or in the early morning hours.

A study from Germany that recorded the arrival of every single moth from dusk to dawn found the busiest time around 23:00 to 23:30. But only about 57 percent of all moths arrived before midnight, and it took until roughly 2 to 3 am to see 90 percent of them. So if you pack up at midnight, you miss a big part of the night. If you can, keep the light on at least until 2 or 3 am.

Light traps: let the moths come while you sleep

A light trap does the collecting for you. Most traps follow the same simple design:

• A bucket or box as the holding chamber.
• A funnel on top leading into it.
• Clear plexiglass vanes around the lamp. Moths fly at the light, hit the vanes and drop through the funnel.
• A UV LED lamp above the funnel and a battery to power it.
• Egg cartons inside. Moths crawl into the hollows and sit there quietly until morning.

Scientists running light traps sometimes put chloroform into the trap. It knocks the moths out instead of killing them, so they sit still and do not damage themselves overnight. In the morning you go through the catch, take what you need, and everything else wakes up and flies away. The trap does not kill everything that falls into it, which is a big advantage. Chloroform is a hazardous, regulated chemical, though, so this is a research method, not something for a garden shed. A trap with just egg cartons works too, the moths simply sit in the cartons until morning.

One rule you must not break: empty the trap before sunrise. As soon as the sun hits the bucket, it warms up, the moths inside wake up and fly off, and you are left with an empty trap.

What to do with what you catch

Most of what comes to the light I just watch, photograph and leave. For moths I want to keep, the usual field method is a glass jar with a piece of cotton wool soaked with ethyl acetate at the bottom. A moth put into the jar is knocked out within moments and cannot damage its wings.

For large hawkmoths and silk moths, a jar is not enough, they are too strong and can damage themselves. These are usually killed with a small injection of ethyl acetate using an insulin syringe, which is quick and keeps the specimen intact.

From there you have three options:

• Pin it straight away and put it into a collecting box. You can set it later, see How to Pin a Butterfly.
• Put it into a paper envelope, wings folded, the same way as daytime butterflies.
• Lay it on cotton wool in a plastic box. Build layers: a sheet of cotton, moths on top, a paper napkin over them, then the next sheet of cotton. The layers keep the moths from rubbing against each other.

Handle moths with soft forceps, never with your fingers. Their scales come off even more easily than on butterflies. And if you want to rear a moth species instead, a female caught at the light will often lay eggs within a few days, the same way as described in How to Rear Butterflies at Home. If hawkmoths are your thing, have a look at my guide to breeding the Death's-Head Hawkmoth.

Bring your friends

The best light nights I have had were never alone. Set up the sheet, invite a few friends, start a barbecue and let the light do its work. Somebody always spots something new on the sheet, and the conversation between the visitors keeps everyone awake until 2 am without noticing. Children love it too, especially when a big hawkmoth lands.

Mistakes almost everyone makes

• Using white light. UV makes the difference.
• Packing up at midnight. A big part of the night is still ahead.
• Ignoring the moon. Around the full moon the catch is weak. Plan your nights around the new moon.
• Going out on a cold, clear night. Check the forecast first.
• Staring only at the sheet. Walk around the light with a headlamp.
• Running a 100 W lamp from the car with the engine off. Flat battery guaranteed.
• Leaving the trap in the morning sun. Empty it before sunrise.
• Setting up in a reserve. Stay outside protected areas.

Gear list

• A UV lamp: a UV LED lamp on a power bank, or a mercury vapour or blacklight bulb on 230 V
• A big white sheet, or a light tower set
• Power: a socket, a power bank, a car inverter or a generator
• A headlamp
• A butterfly net on a telescopic pole for moths circling the light
• Glass jars with cotton wool, paper envelopes or a plastic box with cotton and napkins
• Soft forceps
• Friends and something for the grill

Questions about your setup? Just write me at info@entomoboxes.com, I am always happy to help.

FAQ

What kind of light attracts moths best? Light with a lot of ultraviolet in it. Moths see ultraviolet, blue and green best, so a mercury vapour bulb, a blacklight tube or a UV LED lamp works far better than an ordinary white bulb. Lamps that combine UV with blue and green attract even more.

What wavelength do I need for a moth light? Ultraviolet between roughly 365 and 395 nm is the standard. The best LED lamps add chips with other wavelengths, usually blue and green, to cover a wider part of the spectrum that moths can see.

What is the best night for moth trapping? A warm, cloudy, windless night around the new moon. Light drizzle does not hurt as long as it stays warm. Cold, clear, windy or moonlit nights are much weaker, and so is any spot near street lights.

How long should I run the light? Ideally until 2 or 3 in the morning. Research from Germany found that only about 57 percent of moths arrived before midnight, while about 90 percent had arrived by 2 to 3 am. Hawkmoths often come right after dusk, other groups much later.

Can I attract moths without killing them? Yes. At a light sheet you simply look at them, photograph them and let them go. A light trap with egg cartons inside keeps moths alive until morning, when you go through them and release what you do not need. Just empty it before the sun hits it.

Do I need a generator? Not always. A UV LED lamp runs from a power bank, and in a garden you can plug into the mains. For a strong 230 V lamp far from a socket you need a generator or a car power inverter, and with lamps around 100 W and more you should keep the engine running so the car battery does not go flat.

Why do some moths land far from the sheet? A strong lamp lights up a large area, and some species settle in the grass or on bushes 10 to 20 m away instead of flying all the way in. Walk around the light with a headlamp every now and then and check the surroundings too.

Is moth trapping legal? In most places, on private land or in your own garden, yes. Nature reserves and other protected areas are usually off limits, and some species are protected. Check your local rules and set up your light outside protected areas.