Catch Moths In A Moth Trap

by Johan J Ingles-Le Nobel
Last updated August 31, 2017

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Although they're expensive to buy, a decent moth trap is an essential item if you're into Lepidoptera, as it will catch you moths on almost any night of the year.

A moth trap is just one of many means that are used to catch insects for insect photography, and making your own mothtrap isn't that difficult although the specific Wickes brand garden tub base that Peter Haynes and I used when we made ours no longer seems to be sold, there are alternatives that should be able to do the job. But the cost of making your own comes to about £100, whereas buying a moth trap will cost you about £300. Just beware of the bulb, make sure you get the right one.

Using a Moth Trap

Moth traps are very easy to use. You set them up 1hr before dusk or so, and use a timer to keep the light on until 30 minutes after dawn. to calm moths down, transfer them into specimen tubes and store them in the fridge

A lot of moths do fly before dusk so starting it before nightfall will catch these. Make sure you have a rain guard on there if it's likely to rain in the night, then empty the mothtrap at your leisure in the morning.

To calm moths down to be able to take macro photographs, transfer them into specimen tubes and store them in the fridge for a few hours. Although some people object to this, this simply lowers their metabolic rate and doesn't harm them (in fact it prevents damage because they don't try to fly so the scales don't fall off). In 15 years, chilling moths has not caused me a single moth death.

Robinson Moth Trap

Moth trap

Robinson Moth trap with rain guard. A Robinson is a relatively expensive purchase but once you have one you'll use it for ever and never need to replace it. I usually catch about 100-200 moths on most nights, but 500+ when the conditions are perfect - no moon, high nighttime temperature, no wind and high humidity. June is the height of moth activity in the UK.

A Robinson mothtrap is a big plastic tub with a funnel-like entrance below a bright light source.

The light source attracts moths, and as they fly into the light they fall down the funnel into the trap.

People normally put egg carton boxes inside the mothtrap itself, and as moths fall down into the trap they'll sit on those until the morning, at which time you can unload the moths at your leisure. Mothtraps also attract other nocturnal insects and even the occasional wasp.

Moth trap catches vary according to the months. During Spring and Summer I can catch 100s of moths in a trap, but during the winter months you will catch a handful at best.

Moths do fly all months of the year though, and as surprising as it sounds you can even catch them in the middle of winter.

DIY Moth Trap Tips

Making a DIY moth trap takes a little work but all in all it really isn't too difficult. The key component is a large black garden tub with a diameter of 50-60cm or so, and depth of about 50cm. Avoid tubs with large holes in the bottom, or cover them up with tape before use otherwise the moths will escape. The new softer plastic type tubs available 2017 that seem to have handles look quite handy for carrying, although you do want a rigid tub rather than flexible plastic. That said, if desperate, these will do... although a dustbin costing a tenner can also easily be cut down for the purpose if you want something more rigid.

On top of the tub you will need to fashion a clear top with a gap to allow space for a bulb and bulb support. I made my clear top from 1mm polycarbonate, which is a highly flexible clear plastic and quite pricey alas. Just google for it and there are plenty of plastic suppliers around. Buy a sheet 2 metres by 1 metre and you'll have more than enough. My clear top sits inside a rim round the tub made from 3cm trunking (white plastic used to cover ugly cables) and is attached with screws and washers all the way round. It may take a couple of attempts to get the clear top right and you might want to map it out and use some spare material or cardboard first to make a template to cut the polycarbonate against.

Making a DIY moth trap takes a little work but all in all it really isn't too difficult

The bulb apparatus sits inside the clear top, and I used a large beer brewing funnel of which I cut off the bottom to support the bulb inside. Look for a large 12 inch funnel with a rim if you can, don't skimp on the size for this otherwise your light construct will block the small entrance. Make absolutely sure that the funnel can rest on the clear polycarbonate top, and that there are no gaps for moths to escape. You want quite a tall funnel rather than a flat one - a steep angle makes it more likely your moth will fall inside.

The electrics can seem complicated and as always, take advice from an electrician or buy a premade kit if this is not your area of expertise. In a nutshell though, MV bulb come in two variants, one which needs a choke and another that doesn't (ie blended MV). I have both, and it is more convenient to use one that does not require a choke, but both are perfectly doable. A choke is simply a cup-sized electrics unit that is added into the circuit that is required for to start up certain types of bulb gradually, you should ensure that you have good diagrams etc explaining the circuit required for the choke and bulb. You need the right choke for the right bulb, buy one that is rated for the wattage of your bulb.

Find a source for old fashioned cardboard egg boxes, and pyramid these on top of each other inside the trap so that when moths come into the trap, they have a surface to rest on

For the bulb, you might be best off just buying the electrics from Anglia Lepidopterist Supplies, and attaching it to a metal strip that is in turn attached to the funnel. Go for 125MV, don't bother with actinic. I personally have a blended bulb to avoid the need for a choke, but these do run very hot (which can melt plastic) and in hindsight I'd recommend a colder MV bulb. The end result is the ability just to lift the funnel in and out when it's time to do the trap. My cabling comes back out the top and I have a 24hr timer on the other end to be able to control the trap. Lastly, you'll want too add some vanes, which are 4 upright sheets of white plastic at 12, 6, 6 and 9 'o' clock looking down at the trap. For an all weather trap, add a large circular rainguard on top of these.

Lastly, you'll want to find a source for old fashioned cardboard egg boxes, and pyramid these on top of each other inside the trap so that when moths come into the trap, they have a surface to rest on or underneath that makes it complicated for them to get back out. build these right up to the tunnel and include a bit of a space between them so that moths come into the trap and go between the eggboxes and find it easier to stay inside the trap on the reverse side of an eggbox than to find their way back out. You can also stack some up against the trap to catch the stragglers outside.

When you run the trap at night, have some sort of wooden plank set upright against the trap blocking you from the light so that you can approach the trap as it's lit without having to look directly at the light source. UV is damaging to eyes and you don't want to be looking at the bulb too much. I often go outside last thing before going to bed, as not all moths will find their way into the trap and it's easy to pick them up from walls, the plank, the side of the trap etc and put them in. If you put your trap on a white sheet then it's easier to see the moths that have landed short of the trap.

A typical catch during the warmer months in the UK is 50-100 moths per night, and over the season you should expect 100-200 species. Sometimes you get bumper nights when all the conditions are perfect and I've caught more than 500 in one trap one night myself

You might want to run your moth trap out in the field and for that you'd need a portable power generator. There are plenty of portable petrol generators that will give you a whole evening's trapping with your trap if you are out in the field and these should not have to cost more that £200 or so (2017). Look for one that can drive your bulb for at least six hours, that is easy to transport and that doesn't make too much of a racket. If you do leave the trap out overnight in the field, think about placing it in a spot that doesn't get the morning sun, which can overheat the inside and bake the moths in the trap waiting for you to come along and empty it and of course, if it is unattended, you do run the risk of theft, especially generators.

Do give your mothtrap lines of sight into various habitats for the maximum diversity of moths. More habitat types, more moth types. Placement at the boundary between various habitat types is optimal. Moths fly at a variety of heights with smaller moths flying lower, so for the maximum effectiveness make your trap be seen at low level a few hundred metres away.

Parts Needed For a DIY Robinson Moth Trap

plastic tubLarge plastic gardening or rubble tub, typically about 50-60cm wide at the top and 50 cm high. Used for the base and to contain the moths, you'll need to add a rim at the top so that you can shape the clear polycarbonate in such a way to rest inside the rim and to support a large funnel with attracting light. DIY and gardening stores are the most common place to find them, although amazon does them as well.

trunkingTrunking, a plastic strip material that is normally used to hide cables such as internet cat5 cables running up and down walls. Trunking is normally one inch wide and has two sides to it, this was the cheapest bendy plastic material that I could find at the time that didn't cost the earth and that I could shape round the outside of the top rim of the tub above. Placed on the outide, the trunking adds a rim so that you can rest the polycarbonate doughnut shape on the inside in a pyramidical cone type shape and rest the funnel on top of that, on which the light is fixed. I fixed the trunking on the outside of the top of the tub using a handful of one inch nuts and bolts.

polycarbonatePolycarbonate sheet, 1mm thick. Clear is nice because you can see into the trap although in all honesty clear is not 100% essential. Plenty of suppliers online and on eBay. Polycarbonate sheeting is very bendy clear plastic - used to make the top of the moth trap out of, and what the funnel rests on. Basically you have to cut out a tall o doughnut type shape, then join the ends together so that it stands up and you can rest the funnel on the opening. Use scissors to cut this material - sawing doesn't work as well. I made the top part out of one single piece although others recommend doing this in two halves and attaching them together. Both work.

funnelLarge funnel, the largest you can find. Larger is better and the beer-brewing industry seems to have a monopoly on large funnels. You'll want to cut the spout away anyway so that part of it matters little, but some sort of lip at the top is useful so that the funnel sits nicely on the polycarbonate and doesn't let moths escape. Colour doesn't matter, but I wouldn't use metal as it conducts heat too easily.

Mercury vapour bulbMV bulb - although they're being phased out in Europe there seem to be plenty available from European or US ebay suppliers. Obviously get one that you have the right lamp fitting for. They cost about £20 from ebay, but blended ones that don't require ballast are a bit spendier. Often advertised with a cool colour temperature, they tend to have a screw fitting and be twice the size of normal household bulbs.

moth trap electricsElectrics - although you can make these yourself if you are skilled, you might just want to save yourself the trouble and order all the premade parts together here. You can also order some extra bulbs from here and as they are phased out in the UK now this is probably a really rather sensible idea. In terms of electrics you need cables, ballast (if required, depends on your bulb), bulb fitting and mains plug. The choke unit should be rainproofed and longer cables rather than shorter always come in useful. For safety add in an RCD (residual current device) but this is optional.

metal stripStrip of metal for lamp holder. You obviously want to attach the lamp holder onto something and attach it to the funnel. I used a couple of nuts and bolts to add my strip to my funnel, and used a spare piece of metal that I happened to have lying around the house. If you are stuck for a metal strip you can always go and scrummage around a DIY or model shop for strips of metal, although you could also try something like a brass strip or metal strip found on ebay, then drill the holes through for the nuts and bolts. You don't want the strip too wide as it'll make the hole for the moths to fall down smaller, one inch is wide enough, as long as you can fit the bulb holder onto it. Buy the holder first then decide what width you can get away with. You'll probable need about 50 or so cm, and then bend both ends so that it can be attached sturdily to the funnel.

Skinner Moth Trap

Skinner moth traps operate on much the same principle as a Robinson trap - big bright bulb attracts moths which fall into box. But a Skinner trap tends to have a slit rather than a hole, be made of wood and be rectangular, whereas the Robinson is larger, round and made of plastic. All this really reflects is the fact that the Skinner was the precursor of the Robinson, nothing more -- I've made both and the catch is broadly comparable when using the same bulb.

Heath Moth Trap

The Heath trap is a mini version of Robinson and Skinner traps, and portable for use out in the field. Typically the light source is a low wattage (15W or so) actinic tube. I have not had a great deal of success using actinic myself.

Moth Trap Ethics

  • Don't ever trap on consecutive nights. Catching and recatching the same moths deprives them of a chance to feed and mate.
  • Be considerate of your neighbours. Not everyone wants a bright light shining all night.
  • Release your moths into some nice dense vegetation where they don't get gobbled up by the first bird that comes along.
  • Some bulbs are hot when they're on. Consider adding a guard so that moths don't get fried.

Best Months

In the UK, moth traps are especially effective between May and October, and the height of the moth season is June and July. That said, moths are on the wing every night of the year, and believe it or not I've never set a trap and had nothing caught the next morning. The best nights are windless, moonless, warn and humid.

Other Methods

Moths can also be lured using pheromones, or more traditional means such as wine ropes and sugaring. Sugaring is remarkably effective for 'old lady' moths - I once had a patch covered with these in the garden from a sugaring experiment. Never seen them in a MV trap, ever!

Moth Trap Bulbs

Various types and wattage bulbs are used in moth traps, some of which are more convenient than others. Probably the most convenient is the blended MV bulb (Mercury Vapour), because these do not require any control apparatus (a 'choke') and can be connected directly to the power supply. These come in variants up to 500W although higher wattage does not assure greater success - it just means the moths will come to rest further away from the trap (and the bulbs get very hot). The best option is a 125W MV bulb in terms of catch, but these do require a control mechanism. Actinic bulbs are fluorescent, and my experience of these is not great - they catch a fraction that other bulbs catch.

Actinic or MV Trap?

I have both, and although the Actinic trap catches different species than the MV trap, the MV trap catches at least ten times as many. I'd stay with MV if I were you. Actinic lighting peaks in the 420 nanometer range and emits a fluorescent blue light - it's the light that comes out of those big old overhead fluorescent tubes in offices. The flipside is though that the light isn't nearly as bright so might be more appropriate if you live in a suburban settings where bright lights would annoy the neighbours.

Ideal Conditions

There are various factors that seem to affect how many moths are caught. The best nights are moonless, windless, warm (above 12 DegC) and humid nights in Spring. In the UK there is also a peak in the autumn but that tends to be because there is one particular moth on the wing at that time, which is attracted to light and of which there are millions. Rainy nights are best avoided because it might either crack the bulb or go into the container and drown the moths.

Eggs

As you run a mothtrap, you will catch moths which are in various part of their lifecycles, and some may perish during the night when they were caught because they were at the end of their natural cycle. This is sad but normal, although obviously you should do everything you can to avoid accelerating their demise. You will catch moths in all manner of condition - some will be fresh and in perfect condition, whereas others will be bald! it tends to be the older moths that have lost scales and are balding, although exactly why is open to some debate (I've heard it mentioned that it maybe due to crawling into small spaces). You may even catch a moth that is ready to lay its eggs and it is not unknown to have eggs laid on the eggboxes inside the trap.

Kids

Kids love mothtraps (mine do). It's a great surprise to them that there should be so many butterfly-like insects out and about at night, and they take a lot of pleasure out of having some of the showier ones on their hands when we open up the trap in the morning. There's always a nice bit of oohing and aahing when the big red hawkmoths start appearing in the traps. Thoroughly recommended as a way of teaching children about your local wildlife.

Using A Sheet

What should be noted is that you don't necessarily need a moth trap to see moths at night, and in fact a big old moth trap may not even be the most ideal form of mothwatching, especially in tropical locations where the haul is likely to be too much and too large to get into a small mouthed moth trap anyway. A perfectly good way of looking for moths in oriental climes is just a white sheet suspended from some supports, with a MV lamp below, be it diesel or battery powered. This can (and is) also be used in temperate climes but the haul doesn't tend to be as large or as plentiful there.

Comments (9)

Article: Moth Trap
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Sam says...
I am looking into a cheap version of a moth trap to introduce me to moth trapping but cant find anything any ideas do LEDs work
Admin:
I've never tried LEDs myself so don't know for definite. They're not very bright so I'd have thought they'd be of limited use at best. But I'd be delighted to be proved wrong. Anyone?
16th October 2017 5:51pm
Ian says...
Hi Johan, I'm intending to have a go at the DIY Robinson, and wondered why (or if) i "will need to fashion a clear top" -- what's the benefit of having it clear? Looks like clear materials are actually easier to source, but i wasn't sure what, if any, functional benefits were involved.
Thanks, ian
22nd August 2016 10:21pm
Johan says...
Hello - the clear top just allows you to look in and see what you've got, but no other benefit than that really.
24th February 2017 12:14pm
Lucinda Westwood says...
Hi, I am going to Ecuador this summer and want to do some moth trapping. I can't haul my Robinson trap over there so want to rig up something simple with a bulb and a sheet. The voltage in Ecuador is 120. So far I have not had any helpful advice about what to buy as the voltage seems to be an issue for the equipment sold over here.
28th April 2015 6:50pm
Johan says...
Hi Lucinda - I'd give ALS a call, they might be able to help (angleps.com). DC actinic would be the obvious choice but my yields have been pathetic with actinic. MV on some sort of battery with an inverter if neccessary might be your best bet. You should be able to buy that stuff out there I'd have thought? Enjoy Ecuador, it's supposed to be fabulous for moths :)
29th April 2015 8:23pm
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