A bug zapper, more formally called an electrical discharge insect control system, electric insect killer or (insect) electrocutor trap, is a device that attracts and kills flying insects that are attracted by light. A light source attracts insects to an electrical grid, where they are electrocuted by touching two wires with a high voltage between them. The name comes from the characteristic onomatopoeic zap sound produced when an insect is electrocuted.
In its October 1911 issue, Popular Mechanics magazine had a piece showing a model "fly trap" that used all the elements of a modern bug zapper, including electric light and electrified grid. The design was implemented by two unnamed Denver men and was conceded to be too expensive to be of practical use. The device was 10 by 15 inches (25 by 38 cm), contained 5 incandescent light bulbs, and the grid was 1⁄16-inch (1.59 mm) wires spaced 1⁄8-inch (3.17 mm) apart with a voltage of 450 volts. Users were supposed to bait the interior with meat.
According to the US Patent and Trademark Office, the first bug zapper was patented in 1932 by William M. Frost.
Separately, William Brodbeck Herms (1876–1949), a professor of parasitology at the University of California, had been working on large commercial insect traps for over 20 years for the protection of California's important fruit industry. In 1934 he introduced the electronic insect killer that became the model for all future bug zappers.
Bug zappers are usually housed in a protective cage of plastic or grounded metal bars to prevent people or larger animals from touching the high voltage grid. A light source is fitted inside, often a fluorescent lamp designed to emit both visible and ultraviolet light, which is visible to insects and attracts a variety of them.  The light is surrounded by a pair of interleaved bare wire grids or spirals. The distance between adjacent wires is typically about 2 mm (0.079 in). A high-voltage power supply powered by wall power is used, which may be a simple transformerless voltage multiplier circuit made with diodes and capacitors which can generate a voltage of 2 kilovolts or more. This is high enough to conduct through the body of an insect which bridges the two grids, but not high enough to spark across the air gap. Enough electric current flows through the small body of the insect to heat it to a high temperature. The impedance of the power supply and the arrangement of the grid is such that it cannot drive a dangerous current through the body of a human.
Many bug zappers are fitted with trays that collect the electrocuted insects; other models are designed to allow the debris to fall to the ground below. Some use a fan to help to trap the insect.
These traps are not effective at killing biting insects (female mosquitoes and other insects), being much more effective at attracting and killing other harmless and beneficial insects. A study by the University of Delaware showed that over a period of 15 summer nights, 13,789 insects were killed among six devices. Of those insects killed, only 31 were biting insects. Mosquitoes are attracted to carbon dioxide and water vapor in the breath of mammals, not ultraviolet light. However, there are now bug zappers that emit carbon dioxide or use an external bait, such as octenol, to better attract biting insects into the light.
Research has shown that when insects are electrocuted, bug zappers can spread a mist containing insect parts up to about 2 metres (6 feet 7 inches) from the device. The air around the bug zapper can become contaminated by bacteria and viruses that can be inhaled by, or settle on the food of people in the immediate vicinity. The US Food and Drug Administration (FDA) advises that the bug zapper should not be installed above a food preparation area, and that insects should be retained within the device. Scatter-proof designs are produced for this purpose.
Hand held type
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- Windsor, H. H., ed. (October 1911). "An electric death trap for the fly". Popular Mechanics. 16 (4): 464.
- US US1871978A, Frost, William M., "Insect electrocutor", issued 1932-08-16
- "Electric Chair For Insects Helps Farmers", 1990 march
- Tabanidae Attracted to an Ultraviolet Light Trap, Darrell W. Anthony, The Florida Entomologist, Vol. 43, No. 2 (Jun., 1960), pp. 77-80 Published by: Florida Entomological Society DOI: 10.2307/3492383 https://www.jstor.org/stable/3492383
- Insect Vision: Ultraviolet, Color, and LED LightMarianne Shockley Cruz Ph.D. and Rebecca LindnerUniversity of Georgia Department of Entomology November 2011. https://www.discoverlife.org/moth/OTHER/InsectVision_UVColorandLEDLight.pdf
- Freudenrich, Craig. "Bug Zappers". How Stuff Works. Retrieved 2009-10-22.
- sciencedaily.com: "Snap! Crackle! Pop! Electric Bug Zappers Are Useless For Controlling Mosquitoes, Says UF/IFAS Pest Expert" July 30, 2013.
- "Bug Zappers are Harmful, Not Helpful". Horticulture and Home Pest News. Iowa State University. IC-475 (15). 1996-06-14. Retrieved 2009-10-22.
- "Full text of "Density and Diversity of Nontarget Insects Killed by Suburban Electric Insect Traps"". archive.org. Retrieved 2015-12-29.
- "Can bug zappers help transmit diseases?". HowStuffWorks. Retrieved 30 April 2009.
- Urban, James E.; Alberto Broce (October 2000). "Electrocution of House Flies in Bug Zappers Releases Bacteria and Viruses". Current Microbiology. Kansas State University. 41 (4): 267–270. doi:10.1007/s002840010132. PMID 10977894. S2CID 23790034. Archived from the original on 2013-06-11. Retrieved 2009-10-22.
bug zappers not only pose an immediate threat because of the release of bacteria and viruses, but they also release insect particles which are potential allergens or which cause various respiratory conditions
- "Chapter 6: Physical Facilities; Insect Control Devices, Design and Installation; 6-202.13". FDA Food Code 2009: Annex 3. U.S. Food and Drug Administration. 2009. Retrieved 2013-06-23.
- Does Electrifying Mosquitoes Protect People From Disease? thealtlantic.com, 5 May 2017.
- "Rechargeable Bug Zappers". Zapout (in American English). 2020-04-27. Retrieved 2020-06-26.