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Catch Moths In A Moth Trap

by Johan J Ingles-Le Nobel
Last updated April 16, 2014

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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.

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.

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