| Constructing a Mercury Vapour moth-trap |
| For years, entomologists
have used mercury vapour bulbs to attract moths. Mercury
vapour (MV) bulbs emit a high proportion of their light
as ultra violet and this really does act as a magnet to
moths. An MV light is simply, the best way to attract numbers of moths and is suitable for conducting random sample tests, to determine what species are present in a given site/area or to aid the assessment of resident populations. A single night's trapping in woodland habitat during the Summer months, can result in well over 1000 moths being caught and totals from many suburban gardens can yield similar results in favourable conditions. |
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| Trap
construction Although traps are available to buy from entomological suppliers, building a trap yourself is far cheaper. Constructing a trap is a simple enough procedure and the equipment is usually readily available from most electrical wholesalers and large DIY stores, though selected parts (the choke) may have to be ordered. |
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A basic box measuring 45cm square and 35cm high is built. I used 12mm thick plywood, rather than 6mm for strength and durability. The internal panels are fitted and angled inwards, leaving a gap of around an inch for the moths to enter the trap (shown below). I put hinges on mine for ease of opening. Some commercially built traps are fitted with perspex panels, whilst I have used plywood. Whether there are any actual benefits to be gained by using perspex I doubt. | |||||
| A wooden spar is then
fixed across the top of the box and the porcelain lamp
holder screwed to it's centre. Electrics and wiring The choke and all the electrics, I have housed on the side of the trap to avoid any contact with the ground and dampness. Further to this, I then encased the whole choke and wiring within a rigid plastic container and water-proofed the unit. The choke regulates the amount of power going to the bulb as it fires up, allowing the bulb to warm-up gradually. It should be wired as shown in the photograph directly below. |
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The wiring is fairly
simple. Standard three-core cable should be stripped back
and the wires cut to appropriate lengths for connection
as instructed below. Live (Brown) is connected directly to the choke Neutral (Blue) should be connected to one side of the porcelain bulb holder. An additional length of the same wire is needed to run back to the choke from the bulb holder. Earth (Yellow/green) is connected directly to the choke via one of the fixing screws, on the side of the box. Care should be taken to protect all electrics from water. In many cases where people trap moths in their own gardens, traps are left on all night and checked in the morning. When trapping moths at sites away from home, sessions are often much shorter, but dew can start to form at dusk and cause a problem. |
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| Mercury
vapour bulbs run at very hot temperatures and rain can be
a hazard and an unprotected bulb can explode if it is
particularly cold or heavy. As such, it is wise to cover
the bulb with a heat-resistant glass cover. Portable power supplies In order to provide electricity away from home, I have recently purchased a portable generator - a Powercraft 720 portable generator 650W. It's cheap, but works more than adequately and has allowed me to trap moths in the area using MV light for the first time. |
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