Bug Zappers

by Nick Gromicko, CMI®

A bug zapper is a popular exterior appliance installed by a homeowner or food handler to attempt localized control of flying insect populations. Its name comes from the characteristic “zap” sound 

produced when an insect is electrocuted. Around homes, they are primarily used to kill biting (female) mosquitoes, which create itchy bumps and can transmit the West Nile Virus or encephalitis, malaria and yellow fever. While Popular Mechanics produced a sketch of a bug zapper as early as 1911, it wasn’t until 1934 that parasitology professor Dr. W.B. Herms introduced the electronic insect killer that became the model for all future bug zappers.

How They Work 

 Bug zappers typically consist of the following components:

• the housing, which is a plastic or grounded metal exterior casing that contains the zapper’s parts. It may be shaped liked a lantern, a cylinder or a rectangular cube. A grid design may be incorporated to prevent children and animals from touching the electrified grids inside the device;
• a light source, which is usually fluorescent-type, such as mercury, neon or ultraviolet light;
• wire grids or screens, which are electrified layers of wire mesh that surround the light source. These grids are separated by a tiny gap roughly the size of a typical insect (several millimeters); and
• the transformer, which is the device that electrifies the wire mesh, changing the 120-volt, electrical-line voltage to 2,000 volts or more. 

Bug zappers work by luring flying insects with fluorescent (typically ultraviolet) light into a deadly electrical current. Because the flower patterns that attract insects are better revealed in ultraviolet light, many flying insects that feed on flowers will be drawn to the bug zapper. Before they reach the light, however, they will come into contact with the wire mesh, completing the electrical circuit and disintegrating.

Bug zappers can kill many thousands of flying insects nightly. Some models incorporate a tray designed to collect scattered insect parts, although many models allow the debris to fall to the ground below.

Effective or Not? 

Despite their widespread use, numerous studies have called into question the effectiveness and safety of bug zappers. Two of the more pressing issues are the following:

• Female (biting) mosquitoes and other biting insects are more attracted to the carbon dioxide (CO₂) and water vapor in the breath of animals than to ultraviolet light. As a consequence, standard bug zappers typically kill large numbers of harmless and beneficial insects, such as beetles and fireflies, and ultimately fail to reduce the number of the types of insects that prompt the purchase of a bug zapper in the first place. In fact, one study found that just 0.22% of the insects killed by bug zappers were biting insects, while nearly half of those killed were harmless, non-biting aquatic insects from nearby rivers and streams. The study even found “the probability of being bitten by mosquitoes increases in the vicinity of these traps,” perhaps because the biting insects are actually lured by the ultraviolet light but become distracted by the far more attractive human prey nearby. Some newer bug zappers address this issue by incorporating a CO₂ container at the bottom of the lamp. Other designs attract mosquitoes into a netting device on the outside of the bug zapper that traps the mosquito, and eventually the insect dies of dehydration.
  
• The electrocuted insects are blasted into a fine mist that contains insect parts as well as unkilled bacteria and viruses up to 7 feet (2.1 m) from the device. The air surrounding the zapper may become contaminated with campylobacter jejuni, staphylococci, serratia marcescens, enterococci, and other potentially dangerous organisms commonly carried by flies. For this reason, a bug zapper should never be placed over a food preparation area or in a hospital or any other sterile environment to prevent the potential spread of disease. Children should not be allowed to play beneath an operating bug zapper. Models that contain a tray to catch insect debris are less of a health risk.

Tips for Homeowners 

Bug zappers do not present more of a fire hazard than other electrical devices. Most units have been UL-tested, but, as with any outdoor electrical appliance, care must be taken to ensure that electrical cords do not become frayed or wet.  They should also be connected to GFCI-protected receptacles. 

Inspectors may pass on the following mosquito-control techniques to concerned homeowners:

• Do not allow water to accumulate anywhere in your yard for more than a few days. Eliminate sources of standing water, especially old tires, flower pots, clogged gutters, tin cans or buckets. Fill in or drain ruts, puddles and other low places in the yard. Even holes in trees from rot and hollow stumps can collect water that can harbor mosquitoes. Cover trash containers to keep rainwater out, and drill holes in the bottom of trash containers to allow any water to drain. Repair leaky pipes and outdoor faucets.
• Bug zappers should be cleaned out at least annually to prevent the accumulation of bug parts on the wire mesh, which will decrease the effectiveness of the unit, and may lead to illness if the bug parts contaminate foods, drink or items used by people or pets.
• Keep grass cut short and any shrubbery well-trimmed, as adult mosquitoes use these places to rest and hide.
• Encourage the presence of bats by installing a bat house. These winged mammals pose little danger to humans, and a single brown bat can consume up to 600 mosquitoes per hour.
• Install a fan. Mosquitoes and other flying insects will avoid moving air.
• Wear long-sleeve shirts and pants. The pesticide permethrin may be applied to clothing to protect against mosquitoes and ticks. Beware that while permethrin is relatively safe for people and dogs, it is toxic to cats.

In summary, bug zappers are a common yet controversial means of controlling biting insect populations around the home, and caution should be taken in their selection and use.