Take Back Your Yard From Biting Insects With This Popular Bug Zapper

Help rid your yard of annoying bugs during nighttime gatherings with this classic lantern-style bug zapper that’s effective, efficient, and easy to set up.
Tony Carrick Avatar
Flowtron BK40DK Electronic Insect Killer hanging from gray pergola
Photo: Tony Carrick for Bob Vila

We may earn revenue from the products available on this page and participate in affiliate programs. Learn More ›

If the citronella candles and essential oils aren’t doing enough to drive away mosquitoes from your nocturnal backyard gatherings, then it might be time to unleash this bug zapper from Flowtron on those winged menaces. I put this bug zapper up against five other models over several summer nights in humid and bug-ridden rural North Carolina, and it proved to be the best of the bunch at reducing the population of bloodsuckers in my backyard.

During my testing, I looked at how easy it is to set up the Flowtron, how effectively it attracts and dispatches biting insects, what it was like to clean and maintain, and the impact it had on the aesthetics of my outdoor living space.

While there are certainly some trade-offs with the Flowtron BK40DK bug zapper—particularly when it comes to looks—overall, it outperformed and out-zapped the other bug testers I evaluated.

Flowtron BK40DK Electronic Insect Killer: At a Glance

Flowtron BK40DK Electronic Insect Killer sitting on deck
Photo: Tony Carrick for Bob Vila

Rating: 9/10


  • UV black light and electrified grid design attracts and kills a lot of flying insects
  • Comes ready to plug in and use right out of the box
  • Capable of covering a large 1-acre area


  • Lamp brightness, long cord, and utilitarian looks detract from outdoor living space aesthetics
  • Kills all types of flying insects, including beneficial nonbiting ones

Get the Flowtron BK40DK Electronic Insect Killer at:

What is the Flowtron BK40DK Electronic Insect Killer?

The Flowtron BK40DK consists of a tapered plastic lantern that houses a metal grid and two UV black light bulbs. There’s a ring on the top of the zapper for hanging it up and a small slot at the bottom that holds an octenol bait pack, an attractant that’s effective at luring in mosquitoes and biting flies. The BK40DK is powered by a cord that extends from the top of the unit and plugs into a standard three-prong outdoor GFCI outlet.

The Flowtron’s operation is simple. After it’s plugged in, the bulbs turn on and begin to attract flying insects. When the bugs fly toward the light, they come into contact with the electrified grid, which zaps them with high-voltage electricity, killing them instantly. According to Flowtron, the BK40DK is effective at reducing the flying insect population over a 1-acre area.

How easy is the Flowtron bug zapper to set up and use?

Getting the Flowtron bug zapper up and running is easy, as it comes fully assembled inside its box. All I had to do was find a place to hang it. Per the manufacturer’s instructions, there should be a buffer between the bug zapper and an outdoor living space, so I hung the Flowtron from a bird-feeder hook in my backyard about 30 feet or so from my back patio.

Unfortunately, this made it more difficult to plug it in. Given that the cord extending from the Flowtron is less than a foot long, I had to use a 40-foot extension cord to plug it into the nearest outdoor outlet. I wasn’t a big fan of this; the cord running through my yard was unsightly, plus it created a tripping hazard.

The only other assembly needed for the Flowtron was inserting the octanol cartridge, which slides easily into the cartridge holder on the bottom of the unit. The cartridge lasts about 30 days and costs about $15 for a replacement three-pack.

Flowtron BK40DK Electronic Insect Killer glowing blue at night
Photo: Tony Carrick for Bob Vila

How does the Flowtron BK40DK perform?

It doesn’t take long at all for bugs to make a beeline for the Flowtron’s black light bulbs. Just minutes after being plugged in, the zapper began registering kills. Determining just how effective the zapper is at killing is a simple task, as it registers a sizzling pop for each insect it claims. Flowtron says the BK40DK will attract bugs in a 1-acre area, and it appears to do just that. After about 15 minutes, there was a steady flow of victims heading to the zapper.

Of course, all of that bug zapping isn’t of much use if the Flowtron isn’t preventing the insects from biting you. Although I found that the mosquito activity around me on my back patio declined noticeably with the Flowtron on patrol, I did still suffer a bite or two while it was on. That said, the effect was impressive, considering that my home backs up to a densely wooded area.

Is the Flowtron bug zapper well designed?

The Flowtron is designed with one thing in mind—thinning out a population of biting insects, which it does very well. It is not, however, made for adding to the visual appeal of the yard. The fluorescent blue light is very bright, and the Flowtron has a utilitarian look. Some users may also be turned off by the constant popping noise that the Flowtron registers as it’s taking out insects. In short, if aesthetics are paramount in your backyard, then you might want to look for a different means of killing or warding off biting insects in the outdoor space.

Safety is an issue when it comes to bug zappers. Bug zappers put out about 2 amps of current, which is enough to give a person a good shock and even minor burns, so it’s crucial that these devices are designed to prevent kids, adults, and pets from touching the grid. A guard surrounds the Flowtron BK40DK’s bulbs and grate, preventing fingers or paws from reaching the fluorescent bulbs. Despite that safeguard, it makes sense to keep the Flowtron BK40DK at a height that’s out of reach for pets and small children.

Is the Flowtron BK40DK worth the money?

With a price tag of around $60, the Flowtron BK40DK is certainly more expensive than citronella candles or bug repellent. Those who deal with minor mosquito issues might be able to get by with a smaller and less expensive bug zapper. That said, if non-zap methods or smaller bug zappers simply aren’t working and there is a large area to cover, then this zapper is worth every penny.

The Flowtron BK40DK is a much more affordable option than periodic professional mosquito treatments, which can run between $40 and $100 per month. Just keep in mind that bug zappers won’t eliminate all of a yard’s pest problems. I still suffered a few bites even when the BK40DK was going full force.

Flowtron BK40DK Electronic Insect Killer with blue light on
Photo: Tony Carrick for Bob Vila

Is the Flowtron BK40DK right for you?

The Flowtron is an excellent bug killer, but it’s not ideal for all properties. The size and brightness of the BK40DK are most suitable for properties with enough land to create a buffer between the outdoor living area and the zapper. Remember, the bug zapper will attract all manner of insects to the light. If you’re in close proximity to it, you’ll be sitting among that swarm of insects, which defeats the purpose of having a bug zapper.

The Flowtron is also a good option when a mosquito problem is significant. Those dealing with only a stray mosquito or biting fly here and there can probably get away with a smaller bug zapper or some form of insect repellent.

I should also note that the Flowtron kills indiscriminately, which is one of the major criticisms of any bug zapper. While it will eliminate biting insects, it will also take out everything else that’s attracted to the zapper, including many beneficial nonbiting insects. With that in mind, it’s best to limit the time the zapper is in use to nights when you’re outdoors. For those who find the collateral damage that comes with bug zappers to be off-putting, it’s best to consider some of the more environmentally responsible alternatives to keeping mosquitoes at bay.

Where to Buy the Flowtron BK40DK Electronic Insect Killer

Get the Flowtron BK40DK Electronic Insect Killer at:

Meet the Tester

Tony Carrick is a freelance writer specializing in home improvement, landscaping, technology, home security, and design. His articles have been featured on such sites as Angi, Popular Mechanics, Futurism, 360 Reviews by U.S. News & World Report, Switchful, and more. Tony has conducted rigorous product testing on everything from power tools to home security systems to backyard grills. Living in the South near a heavily wooded area, Tony is all too familiar with the struggle to fend off mosquitoes.


Tony Carrick Avatar

Tony Carrick

Contributing Writer

Tony Carrick is a freelance writer who has contributed to since 2020. He writes how-to articles and product reviews in the areas of lawn and garden, home maintenance, home improvement, auto maintenance, housewares, and technology.