Ugh. Flies. It's that time of year when we're particularly plagued by the beasties. Are you thinking of getting an electronic zapper to turn flies into fries? Read on before buying...


How they operate.

Zappers work by attracting flies using a UV light source. Next to the UV light are two grid-like electrodes, one of which is connected to a high tension transformer which ramps up the voltage (potential) of that electrode to a couple of thousand volts, albeit at a relatively low current. For the sake of simplified explanation, the other electrode has a potential of zero volts so the potential from the charged electrode wants to 'jump' to the non-charged electrode but cannot do so because both are separated by an air gap of a few millimetres. Air is a good insulator and it would probably take a couple of thousand extra volts to allow the low current to break down the resistance of the air and arc across the gap naturally, however should a fly stray across the gap then the lower resistance of it's body allows the high voltage to zap across it providing a momentary path for the current to traverse the gap. This current path remains open until the fly has been destroyed, which happens in a matter of milliseconds with a satisfying audible 'crack' as the air immediately around the fly becomes superheated by the localised explosion of high voltage discharge. The end result is a vapourised or largely burned out fly dropping to the collection tray or melted to the electrode. It ain't pretty.

To change the bulb or clean out the corpses, a safety switch is incorporated which cuts off the high voltage to the electrode when the casing is opened to prevent you getting zapped yourself.

I've had a commercial grade zapper in a discrete corner of my dining room for the last five years and it's great. That said, there are limitations to these things that any potential zapper-purchaser should be aware of before pulling out the credit card.


Don't buy cheap zappers.

The zappers sold for £20 or so in DIY stores or in those dreadful mail-order supplements stuck in the middle of the TV guide usually don't work too well. To cut costs they often use UV blacklight bulbs which emit the wrong kind of light from the UV spectrum to attract insects. If you look at a cheap one, compare the light to the kind you see behind a butcher's counter or in a restaurant and you'll notice the commercial zappers have a much larger, brighter lamp with a lighter purple colour. Although the cheap zapper might attract the odd insect, it won't solve your problem and doesn't represent value for money. If zapping is your thing, invest in a commercial unit. You'll pay at least fifty quid, probably much more, but it will actually do what it's supposed to.


Site them carefully.

You don't want a zapper immediately inside the door of your house as it may end up attracting in flies which would otherwise have happily stayed outside and not bothered you. Although you may need your zapper in a kitchen or dining room, it should not be placed directly over areas of food preperation/consumption as debris can be thrown out from an exploding fly. Tiny though they may be, nobody likes the thought of fly parts spinning out into their pudding!


Here's the catch.

Not all flies are attracted to UV light. Unfortunately the most annoying flies such as mosquitoes, those big black buzzing house flies and green/blue bottle flies are all uninterested in light. For some reason we get plagued by the big black flies in our kitchen. I don't know why. Other houses I visit with open doors/windows don't seem to have 'em buzzing about and it may be because our L-shaped living/dining room/kitchen has just one way in and out rather than a through draught, but whatever, these things get in and don't go anywhere near my commercial zapper. I have to deal with them using flypaper and a swat. Even then they don't appear particularly attracted to the flypaper and seem to end up blundering into it quite by accident more than anything else. That said, I do hear plenty of 'cracks' from the zapper over a summer evening, but the victims tend to be small moths or the wispier, lighter flies that aren't so much of a nusiance as the big annoying housefly.

A zapper is also only going to be useful during the dark for the most part. If the summer sun is streaming in through the windows then the UV light will be less effective. Besides, many of the insects attracted to light come out at night looking for the moon so don't expect to hear a report of high-voltage insect death so much during the day even if the buggers are dive-bombing you in numbers.

In effect then, a good fly-zapper represents only part of the solution. If winged insects are a problem for you then a good zapper will help deal with some of them, but other traps which use scent rather than light as a bait may also be required to help keep you fly-free in the summer.

 If you want to go ahead with the installation of a good zapper, contact me to discuss your requirements.