Do Bug Zappers Work? The Insects They Actually Kill
Bug zappers work at killing insects, but not the ones that bite you: in the best known study, only 31 of 13,789 insects killed by backyard zappers (0.22 per cent) were biting flies. Female mosquitoes find people by the carbon dioxide we breathe out, not by ultraviolet light, so a zapper on the patio does not lower the number of bites. In a controlled Indiana trial, biting did not fall even after 11 days of continuous operation. For mosquitoes, repellent, fans and emptying standing water do more; indoor UV traps are a reasonable tool for house flies.
The crackle of a zapper on a summer evening feels like proof it is doing its job. Entomologists have been counting what actually lands in the tray since the 1970s, and the answer has not changed in half a century. This guide sets out what zappers kill, why mosquitoes mostly ignore them, where a light trap does make sense, and what to use instead.
What the studies found
Every controlled count of zapper catches points the same way: thousands of insects per night, almost none of them biting.
| Study | Where and when | What it found |
|---|---|---|
| Nasci, Harris and Porter, Mosquito News, 1983 | Backyards in South Bend, Indiana | Zappers killed 3,212 insects on an average night, only 3.3 per cent of them female mosquitoes; biting did not fall after 11 days of continuous operation |
| University of Notre Dame studies, summarised by the American Mosquito Control Association | Indiana, a full season each | Mosquitoes were 4.1 and 6.4 per cent of the daily catch |
| Frick and Tallamy, University of Delaware, Entomological News, 1996 | Six suburban homes in Newark, Delaware, summer 1994 | 13,789 insects killed; 31 biting flies (0.22 per cent); 18 female mosquitoes |
| UF/IFAS Florida Medical Entomology Laboratory, reported 1997 | One zapper, one night, Florida | About 10,000 insects killed, eight of them mosquitoes |
| Urban and Broce, Kansas State University, Current Microbiology, 2000 | Laboratory room with house flies | Zapped flies released bacteria and viruses into the air on fragments |
Only female mosquitoes bite, so the count that matters is females. In the Delaware study the trays held 43 mosquitoes in total across a summer of sampling, 25 of them males. That is 18 biting mosquitoes from six yards, every one of which sat within 3 km of water and within flight range of breeding sites.
What a zapper actually kills
Frick and Tallamy identified their catch to family level, which is why their paper is still the reference everyone quotes. Species from 12 orders and more than 104 families went into the trays. The biggest single group was non-biting midges, aquatic insects that look like mosquitoes but cannot bite, followed by leafhoppers, caddisflies and moths.
The paper counted 1,868 predators and parasitoids (13.5 per cent of the catch), including ground beetles, rove beetles and braconid wasps, insects that eat or parasitise garden pests. Non-biting aquatic insects made up 6,670, or 48.4 per cent. The seasonal mean was 445 insects per trap per night of at least two hours.
The authors also ran a deliberately rough calculation: if 4 million zappers ran for 40 nights a summer, more than 71 billion non-target insects would die in the US each year. They flagged it as speculative, and it should be read that way, as a sense of scale rather than a measured figure.
Why mosquitoes ignore the light
Do bug zappers kill mosquitoes? A few, but not enough to matter, and the reasons are well documented.
- Breath beats light. The American Mosquito Control Association describes carbon dioxide as the most universally recognised mosquito attractant, drawing mosquitoes from up to 35 metres. Frick and Tallamy cite a run of studies back to 1941 finding exhaled carbon dioxide far more attractive than light traps. The Indiana trial found people near the devices were consistently more attractive to mosquitoes than the zappers. Our guide to what attracts mosquitoes covers the full sequence of breath, skin odour and colour.
- Many species do not come to light at all. The Delaware paper notes that many mosquito species are not attracted to light traps, and the lamps sold in zappers, which emit plenty of visible light, are less attractive to mosquitoes than pure ultraviolet.
- Those that approach are rarely electrocuted. A mosquito drifting towards a trap often does not hit the grid.
UF/IFAS entomologist Jonathan Day put it bluntly in 1997: zappers will not control mosquitoes or other biting insects such as horse flies and deer flies, and he called them a total waste of money for that purpose.
The season problem in our data
Zapper catches also run on the wrong calendar. In Delaware, the average catch fell from 1,304 insects per trap on 20 June to 106 on 27 August. Mosquitoes, by contrast, build through late summer.
Our analysis of US iNaturalist research-grade records shows mosquitoes at 147 on our index in July, 168 in August and a peak of 182 in September, nearly twice their yearly average share of what people record. Records of biting midges, the no-see-ums, peak earlier, at 314 in June, though that line rests on only 309 records and is noisy. House fly records climb into autumn, peaking at 225 in November. These are records of when people photograph and identify insects, not trap counts, but the pattern matches the Delaware finding: biting insects made up a slightly larger share of the zapper catch as summer went on, rising from 0.26 per cent on 20 June to 1.88 per cent on 20 August, yet never a meaningful one.
Are bug zappers bad?
Beyond not working on mosquitoes, there are two concerns worth knowing about, and neither calls for alarm.
Insects you might want to keep
The non-target losses are real. Predators, parasitoids and aquatic insects that feed birds, bats and fish make up most of a zapper’s catch. If you run a zapper all season near water, you are removing far more of those than mosquitoes.
Fragments in the air
Kansas State researchers loaded house flies with a harmless marker bacterium and a bacterial virus, then zapped them in a closed room. Flies contaminated on the outside released one in every 10,000 of the microbes on them; flies that had eaten them released one in every million. The authors concluded zappers could play a role in spreading infectious agents, depending on how the insect was contaminated, and in 1999 the team advised against using them in food handling areas, hospitals and day care settings. It is a reason to keep a zapper away from where food is prepared or served, not a reason to panic about one at the end of the garden.
Bug zapper vs mosquito trap
Mosquito traps that release carbon dioxide or a skin-odour lure are a different technology from a zapper, and the evidence for them is better, though still mixed for an ordinary yard.
| UV bug zapper | CO2 or lure mosquito trap | |
|---|---|---|
| What draws insects | Ultraviolet and visible light | Carbon dioxide, heat or a synthetic skin-odour lure |
| Main catch | Midges, moths, beetles, leafhoppers | Female mosquitoes and other blood feeders |
| Evidence it reduces bites | None; Indiana trial found no fall in biting | Some: 64 to 87 per cent fewer landing tiger mosquitoes in one Italian trial with 7 or 8 traps per site |
| Where it fell short | Mosquitoes prefer people to the device | A trap perimeter did not give the same reduction around homes in Gainesville, Florida |
| What it takes | Power and a tray to empty | Continuous running all season, careful placement, lures or gas to replace |
The Italian study, Englbrecht and colleagues in 2015, used dense trap networks, one trap per 150 to 350 square metres, against the Asian tiger mosquito, which breeds in small containers close to homes. USDA researcher Daniel Kline found propane traps significantly cut black salt-marsh mosquito annoyance along a trail on an isolated Gulf island, but a perimeter of the same traps did not achieve the same level of reduction in a residential area. The pattern is that traps help most where mosquitoes are produced locally and are not constantly flying in from elsewhere. One trap in a suburban yard is a modest tool, and it does nothing about the breeding site next door.
Where a light trap does make sense: flies indoors
Do bug zappers work on flies? Indoors, light traps catch house flies well. In a 2019 USDA trial published in the Journal of Insect Science, Hogsette and Cilek released house flies into closed rooms with a single UV light trap; one model caught about 83 per cent of the released house flies within 24 hours and another caught 100 per cent. Both used glue boards rather than an electric grid, which avoids scattering fly fragments. The traps were set about 90 cm off the floor, following earlier work showing the best catches within 1 m of the floor.
That is the case for a glue-board fly light in a kitchen or garage. It is not the case for a zapper outdoors in daylight, and a sudden indoor fly problem usually has a source to find, which our guide to flies in the house all of a sudden covers.
Mosquitoes indoors and no-see-ums
Do bug zappers work on mosquitoes indoors? There is no good evidence they do. Indoors, you are still the strongest attractant in the room. Screens, closing gaps, and a fan in the bedroom do more; our guide on how to get rid of mosquitoes in the house walks through it.
Do bug zappers work on no-see-ums? Barely. Biting midges were a target the Delaware authors named, yet the trays held 12 female biting midges all summer against 4,612 non-biting midges. UF/IFAS notes adults are only 1 to 2 mm long (0.04 to 0.08 inch), and that regular window screens do not keep them out. DEET-based repellents are the main protection UF lists.
What works for mosquitoes instead
- Repellent on skin. CDC recommends EPA-registered products containing DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol or 2-undecanone, used as the label directs. Do not use OLE or PMD products on children under 3.
- A fan. Michigan State researchers found fan-generated wind strongly reduced mosquito catches at carbon-dioxide-baited traps, mainly by diluting the attractant plume, and recommended fans as a practical way to protect people and pets in a backyard.
- Weekly water checks. CDC advises emptying, scrubbing, turning over or covering anything that holds water once a week: buckets, toys, birdbaths, plant saucers. Our guide to how long mosquitoes live explains why the weekly cycle works.
- Screens in good repair on windows and doors.
- Professional barrier treatment when a yard is badly affected; our mosquito control cost guide sets out what that runs to and how often it repeats.
The other patio staples do not rescue the situation either. Citronella gives only small reductions, as our test of the evidence on whether citronella candles work shows, and living plants do even less, covered in our guide to mosquito repellent plants. Electronic and ultrasonic repellers have failed every field test, as our review of ultrasonic pest repellers explains.
Frequently asked questions
Why do people not use bug zappers anymore?
Plenty still do, but entomologists have long advised against them for mosquitoes. Controlled counts from the 1980s and 1990s found mosquitoes were a tiny share of the catch, 18 female mosquitoes among 13,789 insects in one Delaware study, and an Indiana trial found biting did not fall. Most of the catch is harmless or beneficial insects, and Kansas State research showed zapped flies release microbe-laden fragments.
What’s the best thing to kill mosquitoes outside?
The most reliable step is removing the water they breed in: CDC advises emptying or covering containers that hold water once a week. For adults, a licensed professional can apply a barrier treatment to the vegetation where mosquitoes rest, which typically needs repeating every few weeks. Personal protection still matters, because no yard treatment removes every mosquito; an EPA-registered repellent used as the label directs is the dependable layer.
Is it worth getting a bug zapper?
Not for mosquitoes or other biting flies; no controlled study has shown a zapper reduces bites. A UV light trap with a glue board can be worthwhile indoors for house flies: in a 2019 USDA trial one model caught about 83 per cent of released house flies in 24 hours and another caught all of them. Outdoors, most of what a zapper kills is harmless or beneficial.
What is the most effective device to kill mosquitoes?
Traps that use carbon dioxide or skin-odour lures have the strongest evidence. In a 2015 Italian trial, sites with 7 or 8 lure traps had 64 to 87 per cent fewer tiger mosquitoes landing on people than control sites. But a USDA evaluation found a perimeter of propane traps around homes in Florida did not give the same reduction, so results depend on placement and local breeding. A simple fan also measurably reduces mosquito host finding.
Do bug zappers work on no-see-ums?
Not in any useful way. In the Delaware zapper study, a full summer of sampling at six homes produced 12 female biting midges among 13,789 insects. No-see-ums are 1 to 2 mm long and pass through ordinary window screens, so UF/IFAS advises finer screening and DEET-based repellents. Their bites can be intensely itchy; for a reaction that worries you, ask a doctor or pharmacist.
Sources
- Frick, T.B. and Tallamy, D.W. Density and diversity of nontarget insects killed by suburban electric insect traps. Entomological News 107(2): 77 to 82, 1996. University of Delaware.
- Nasci, R.S., Harris, C.W. and Porter, C.K. Failure of an insect electrocuting device to reduce mosquito biting. Mosquito News 43, 1983.
- American Mosquito Control Association, Frequently Asked Questions.
- University of Florida IFAS News, Electric bug zappers are useless for controlling mosquitoes, July 1997.
- Urban, J.E. and Broce, A. Killing of flies in electrocuting insect traps releases bacteria and viruses. Current Microbiology 41(4): 267 to 270, 2000; Kansas State University release via ScienceDaily, June 1999.
- Englbrecht, C. et al. Evaluation of BG-Sentinel trap as a management tool to reduce Aedes albopictus nuisance in an urban environment in Italy. Journal of the American Mosquito Control Association 31(1): 16 to 25, 2015.
- Kline, D.L. Traps and trapping techniques for adult mosquito control. Journal of the American Mosquito Control Association 22(3): 490 to 496, 2006. USDA ARS.
- Hoffmann, E.J. and Miller, J.R. Reassessment of the role and utility of wind in suppression of mosquito host finding. Journal of Medical Entomology 40(5): 607 to 614, 2003. Michigan State University.
- Hogsette, J.A. and Cilek, J.E. Evaluation of a commercial UV fly light against house flies and stable flies under indoor conditions. Journal of Insect Science, 2019. USDA ARS.
- UF/IFAS EDIS IN626, Biting Midges (no-see-ums).
- Centers for Disease Control and Prevention, Preventing Mosquito Bites.
- The Pest Control Brief analysis of iNaturalist research-grade records, pulled October 2026.
