Budget Bucket Moth Trap
Using light traps to attract moths is a fun and effective way to find out more about moths. In order to encourage more moth recording East Scotland Branch have started a Budget Bucket Moth Trap initiative. This aims to encourage new moth trappers and also those who have not trapped using a mobile trap in habitats away from gardens.
We have designed a simple moth trap using readily available components that allow the total cost to be kept low. It is not going to be as effective as more expensive, professional Robinson and Skinner traps with MV bulbs, but is small, light and a good way to get going. The trap based on a 20 litre bucket with a well fitting lid that can house a large household funnel. There are two lighting options that are both water tolerant, and avoid the cost and complexity of vanes and a rain cover.
We plan to run introduction to moth trapping workshops at which participants will be able to assemble their own trap based on pre-built parts, but we thought it would be worthwhile to publish details of the design and construction of the traps should others wish to make their own.
The two light options that have been designed are shown below.
The first trap option is based on a compact fluorescent bulb that runs off the mains. The wattage of these bulbs, of around 20w, is low enough to also allow the use of a cheap 12v inverter which can enable mobile use too. Two different types of compact fluorescent bulbs are recommended, one an actinic and the second a full white spectrum with up to 40% UV content.
LEDs are creating a lot of interest and are increasingly being used for moth trapping. They are a relatively new introduction and there is still much to learn about them. LED strips provide a relatively easy way to allow a moth trap light to be made and have had good reports from moth trappers. So far it seems that some LED setups can approach those with fluorescent bulbs in some conditions, but often with different catch composition although seem to be less consistent in terms of moth numbers attracted.
Batteries and power
12v based power for lighting is a complex subject. Lead-acid batteries are not cheap, are heavy and have limited life if discharged and recharged too much. There are some that are designed to cope better with this charge cycling but even so have a limited life. The main alternative is to use one of the varieties of Lithium battery which are lighter, have longer but not infinite lifetime, but are even more expensive. Lower capacity batteries are cheaper and lighter, but won't keep the light on for as long which can be a problem particularly in the darker months of the year. When calculating the capacity (in ampere hours (AH)) then lead acid batteries should not be drained to less than 50% capacity. Lithium batteries are more tolerant of more of their charge being use capacity being used.
The compact fluorescent bulbs are mains AC powered, but there are products, called inverters, that will convert from 12v. We have successfully used these 75w inverters for over 10 years. A simple crocodile clip to cigarette lighter socket converter allows attachment of the inverter to a battery or a more sophisticated arrangement with a light sensitive switch as illustrated here is possible. The inverter must be kept dry. Note that the inverters are designed to work from car batteries which are actually up to 14v and so cheaper lithium batteries such as those mentioned below will drop their voltage below 12v as they discharge and the inverter can, or will, switch off.
For LED lighting then cheaper lithium batteries are available from eBay, for example, such as the one shown here. They are often shipped from China. 15,000 or 20,000 mAH capacities are likely to be required, depending on the power of the LEDs and the duration that the light needs to be switched on. (They will not power inverters for the CF bulbs.)
USB power banks and even car jump starter packs can be used. The former, particularly, are often not compatible with light sensitive switches. The USB ports are also only 5v rather than 12v, but for 10w or lower lighting a step-up converter can be used. See the LED light page for more details.