ZZZZzzzzzzzt! It’s strangely reassuring, when queuing at a butcher’s or baker’s counter, to hear the noise of an insect meeting its doom on an ultra-violet light trap. It makes you feel safe in the knowledge that a fly isn’t going to land on the food you are about to buy.
Would you feel the same way if you knew that the zapping noise you hear is accompanied by a cloud of microparticles from the recently deceased insect raining down on the surfaces beneath the trap and bits of the insect shattering and flying off in all directions? Approximately two in every hundred house flies electrocuted on high voltage traps scatters over a metre from where it was killed. Research has suggested that fly traps should be positioned at least 2m (horizontally) to ensure a scatter-free zone around the trap (Pickens, 1989).
Furthermore, you might be eating more than just scattered electrocuted fly parts. Flies carry a wide range of bacteria on their bodies and in 1992 and 2000 two research groups looked at the generation of airborne particles from five commercially available electrocution fly traps. They found that the numbers of airborne micro-particles increased with increasing fly catch, as you might expect, but also that moths generated a much higher number of particles dues to their stronger wing beat and scale fragments from their wings. The other important point from these two studies was that air movement dramatically increases the number of particles detected and the numbers of insect fragments that leave the unit (Ananth et al, 1992; Urban & Broce, 2000).
Watch this video to see what happens when a fly comes into contact with an electric fly killer
Salmonella in your salmon bagel?
Escherichia in your tuna empanada?
There are situations where electrified grid fly traps are the right tool for the job. Controlling flies in a cow shed of a chicken coop as examples. In those situations preventing flies from entering the buildings is not practicable and there is no need to undertake any monitoring- it’s pretty obvious that flies are a problem in these cases. Around human food preparation areas…? There are always better options than falling lumps of fried Musca domestica adding extra protein to your chunky salsa salad.
These traps are common in food preparation areas: their presence is often mandated by best practice guidelines the business is following. The reason they are mandated is to reduce risk of food contamination from flying insects. House flies are capable of transmitting a number of pathogens to our food that can cause disease. However, this risk is reduced far more effectively by glue traps than by high voltage traps because the flies remain intact when captured rather than stunned, maimed or shattered when they come into contact with a high voltage grid. Therefore, using ultra-violet traps with adhesive surfaces reduces the risk of contracting a fly borne disease near food preparation areas.
Anyone associated with food will know, safety is vitally important when operating within the food industry,
I'm a laboratory-based entomologist who works at Rentokil's European Technical Centre. I joined Rentokil in 2008 to set up and run research projects on the control of urban insect pests. Before Rentokil I worked for a consultancy that specialised in diagnosing timber defects in historic buildings, including wood-boring insect infestations and fungal decay. I own far too many books on urban insects and timber pests. When I'm not working you can usually find me playing board games and card games or fencing, occasionally.