Catch Moths In A Moth Trap

by Johan J Ingles-Le Nobel
Last updated May 13, 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 Wicks "garden tub" base that Peter Haynes and I used when we made ours no longer seems to be sold. 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.

Make a DIY Moth Trap

Making a DIY moth trap takes a little work but all in all it 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 holes in the bottom, or cover them up with tape before use otherwise the moths will escape. The new type tubs available that seem to have handles look quite handy for carrying, although you do want a rigid tub rather than flexible plastic. 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. 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 cardboard first to make a template to cut the polycarbonate against.

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. Just make sure that the funnel can rest on and inside the clear sleeve. You want quite a tall funnel rather than a flat one - a steep angle makes it more likely your moth will fall inside. 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. All you now need are lots of old fashioned egg boxes and your DIY Robinson trap is ready to go.

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.

Other Methods

There are a variety of other traps used by entomologists to catch insects, most of which are a very affordable small project. Moths can also be lured using pheromones, or more traditional means such as wine ropes and sugaring.

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.

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 accellerating 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 neccessarily 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 (8)

Article: Moth Trap
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Johan says...
Hello Jim - I have no experience of the bulbs inside the floodlight case myself so unfortunately it'd be a complete guess on my part. Moths come to MV bulbs because of the UV component so if you can, check the spectral emission charts of both the bulb and the housing (some glass blocks UV). If it were me though I'd play it safe and order some proven MV bulbs and chokes from countries where they're still available and for sale - for example Anglia Lepidopterist Supplies or Watkins and Doncaster here in the UK. I'm sure that if you explained your predicament they'd be happy to help. Best of luck!!!
3rd August 2015 10:30am
Jim Duggan says...
Thanks Johan. Yes, I have enquired with ALS as to cost for just the light and fixture and electrical supply system to see if I can incorporate it with my current Skinner Trap. May also try the MV lamp I have without glass cover. Thank you again. Jim
3rd August 2015 1:29pm
Parula says...
Thank-you for this! I particularly liked your comments on refrigerating the moths: "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." Lots of people believe this is unethical or harms the moths nice to see someone show in a very plain sense way that it in fact does not!
12th March 2015 6:34am
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