Building a Robinson type Moth Trap

Moth traps overview / summary

Robinson Trap There are many types of moth traps available, all are obtainable from a range of online sellers, with some of the more common trap designs being of the Heath, Skinner or Robinson type traps. While commercial traps are available, it is very rewarding to design and build your own trap, and they are also fairly straightforward to build too.  Each of the designs incorporates to greater or lesser degrees, combinations of the three main elements of moth trap design which are the triumvirate of; 

• attract
• capture
• retain 

It is generally accepted that the Robinson type moth trap - which utilises a conical design and mercury vapour bulb - is thought to be the most effective of the three, and often yields up to 8 times more moths than some other traps (see Note 2 below).  If you are making your own moth trap I have found it best to experiment with each design based on a combination of your budget, location and the results you wish achieve.  This rough guide shows how I built my variation of the robinson type moth trap. 

Note 1: I have also tried where possible to include links to the items I have used, or to items that are suitable as alternates.

Note 2: This figure is based on my experience, and is somewhat implied on the NHBS www site.  With my home made Heath type and Skinner traps, the yield varies between 20 - 50 moths, with 50 being a good night and an extremely good total.  The blog article on the NHBS www site here suggests that on a good night in excess of 500 moths can be caught in a Robinson type trap.  That is some figure, and is x10 compared to what I get in my heath/skinner traps.  I have yet to test my Robinson type design fully due to the inclement weather, but will update this stat section with my findings when I do.

Note 3: It is worth mentioning that if you plan on building and using this type of trap in the UK, where though our summers are warm, they are also shall we say, not always dry :) then it might also be worth considering adding some form of perspex rain cover to this trap.  MV bulbs are relatively expensive to replace and can easily crack/shatter if they are exposed to rain.  I have not included any form of rain cover in my design here.

My Robinson-esque moth trap build

50L Bin You can use any type of container for your trap, square, round, all black or transparent – each has its own merits.  I have previously used plastic storage containers from B&Q / Hoebase which have worked very well, but for this trap I bought a simple 50L bin from Amazon, it has handles that lift up and over to lock the lid in place which is useful as it makes the trap a lot sturdier when carrying.  I cut out the centre of the lid, which I measured and cut just a few mm less than the diameter of the 10” funnel.

With this particular bin, it doesn’t matter that the lid is curved/rounded across the top but note that this curvature is not flat and has ridges which raise and lower in height.  This means that if you insert a regular funnel over this cut-out, there will be gaps between the lower parts of the lid and the funnel which will allow any moths and insects captured to escape relatively easily. To combat this, I bought a funnel that had a lip of about an inch from the top of the funnel downwards. Funnel  

Note the 1” section from the top of the funnel down – this means that the start of the chamfer of the funnel will be below the lowest point of the ridges in the lid thus closing off any opportunities for moths to escape.  If your container is flat and does not have the same ridges as in the lid I used, then this won’t be an issue for you.  You can see from the 3^rd image where the 1” lip on the funnel covers the ridges on the lid of the bin which are still above the start of the chamfer and are not allowing any gaps to be seen.  I used a jig-saw to accurately cut out the hole in the lid of the bin such that the funnel was a nice snug fit and needed to be pressed firmly into place.  I will eventually install a rain guard/cover and in the meantime having this as a snug fit will ensure rain is not able to seep inside the trap.  it should be noted that some traps also incorporate a type of drain to protect the moths in case of water ingress.

Funnel in lid Some experts suggest that a gap of approx. 2” to 3” is about right to capture and retain moths, and not allow them to escape.  I am using an E27 bulb holder which is going to be supported on a brass strip and situated pretty much at the centre of the hole in the bottom of the funnel (see in a later pic). With this in mind I made sure the hole was large enough for a 2” diameter spacing around the bulb holder itself, and again used my jig-saw to cut out the end of the funnel to the ridge you see on the funnel itself.  The actual size of the hole is important, but not critical: you don't want the hole to be large enough for the moths to be able to easily escape, and not small enough for them not to be able to fit through when captured.

Funnel 2
TIP: it is often better to have a transparent lid on your trap.  Many of the Skinner type traps will have perspex or acrylic sheets on the top for example, and also commercial Robinson traps have a clear lid too.  This is because when (as in my case here) the lid is black, the only light source the moths see having been trapped, is the light that attracted them into the trap in the first place which is of course, outside!  Until the moths are settled and resting in egg boxes or whatever material you have placed inside the trap for them to rest upon, they may still be attracted to the light and head towards it - right back out of the trap, defeating the object! 

Next we need to sort out any electrical wiring, the bulb, its holder and any cables needed.  Please note that if you plan on using the same type as I do in this design which is a mercury vapour bulb – this arrangement also needs a choke i.e. a type of ignition device similar to those used in fluorescent lamp fittings.  It should also be noted that you cannot use the same choke from a fluorescent fitting in these kits.  MV Set

I purchased this mercury vapour bulb, choke and wiring kit from an online supplier, a very helpful chap by the name of Paul Batty (just do a google search and you will find him) – who will assemble all the electricals and wiring for you if needed.

These mercury vapour bulb and choke kits can be expensive, but you don’t have to use this type of bulb for your moth trap, it is best to experiment with several of the alternate types, and you can alternatively use blacklight, UV or actinic type bulbs available from many online suppliers.  These bulb types usually plug directly into a regular E27 large screw in type bulb holder, and the holders can be obtained from most hardware stores such as B&Q, HomeBase and Amazon etc.  I have also built a successful trap that captures dozens of moths and uses a UV aquarium bulb, link here.  This might be a good option as a first test build, they do work very well.

DISCLAIMER - PLEASE NOTE: EXTREME CARE MUST BE TAKEN WHEN WORKING WITH ANY 240V AC ELECTRICAL SUPPLY – THIS IS EXTREMELY DANGEROUS AND CAN KILL YOU.  ANY ELECTRICAL WORK SHOULD ONLY BE CARRIED OUT BY A SUITABLY QUALIFIED ELECTRICIAN.

You will need to decide which bulb you are going to use for your trap and then incorporate a suitable method for securing the bulb into place on your specific design.  The method of attaching/securing the bulb to your unit varies greatly.  Bulbs can be used either way - pointing up or down, just ensure the bulb, holder and any cables are safely and securely fastened on your trap.

Brass Strip I used a thin brass strip which I drilled and attached an E27 bulb holder, then secured this to the underside of the funnel using M3 bolts and washers.  In other designs, I have also used a piece of wood... and duct tape - they all work well.

TIP: If you plan on using bolts, washers and nuts to secure the bulb and wiring to the funnel, I would suggest you locate the flat head of the bolt on the upper side of the funnel and the nut/washer on the underside.  There are then fewer potentially damaging protruding edges for moths to fall onto and possibly injure themselves as they are captured.

E27 Bulb Holder
Connect up all your wiring (see disclaimer above) and run any cables such that they are not protruding anywhere in your design.  Here is the brass strip complete with E27 bulb holder attached to the funnel with the wires securely attached to the funnel using white cable holders.  This helps to ensure no stress is applied to the electrical joints on the underside of the E27 connector when moving the trap.

Also note the heads of the bolts are on the upper side of the funnel.

Veins are utilised for a number of reasons - mainly as an object that the moths will bump into as they head towards the light source, and sometimes they also act as reflectors for the light itself.  Some veins are white, and some designs incorporate a clear plastic design.

Veins 2 For the veins on this prototype design, I used foam board sheet purchased from HobbyCraft.  This foam board is a fabulous material to use for prototyping moth trap designs as it is very cheap and also very easy to work with.  Simply use a sharp knife and preferably a straight edge, taking care when cutting the sheet of course, and cut out to your preferred design.  

There is an ongoing debate as to if 4 veins at 90 deg angles or 3 veins at 120 deg angles is better for attracting moths - simply experiment with your chosen design to see which works best for your trap.

And pretty much, that's it!  Simply insert your bulb and turn the power on, with your design and a little luck I am sure you will be able to attract and capture many moths to your chosen trap.  All the moths I have captured using various traps this year, are catalogued in my Moths Gallery, please feel free to take a look and leave a comment, I always love reading any comments.

Lesser Swallow Prominent Buff Tip

Enjoy, and happy moth trapping!

Moth traps available here:

https://www.nhbs.com
https://butterfly-conservation.org/in-your-area/east-scotland-branch/moth-traps

https://www.angleps.com/mothtraps.php


Poplar Hawkmoth