It is recorded that as far back as 1911, there were prototypes for and plans for an electric 'fly trap' as it was called. The design consisted of several incandescent light bulbs and an electrified grid. The interior of the 'trap' was to be baited with meat according to the unnamed original designers of this device. It was determined to be prohibitively expensive to manufacture, so the idea was shelved. Then, in 1934 the first patent was issued to William Folmer and Harrison Chapin for the design that basically represents today's modern bug zapper. The proper term is electrical-discharge insect control system.
From the point of that invention, the bug zapper has essentially remained unchanged in most of its design elements save for some issues with better safety over the years. The way that these zappers work is that there is a light source, an electrical grid and some type of housing. This is really all there is to them.
What happens is that when plugged in, the light is illuminated and either or both fluorescent and ultraviolet (black light) glow. This glowing from within the bug zapper attracts insects and other flying pests. When they get too close to the grid and hit the wires, they complete the circuit and they are electrocuted. This causes them to instantly drop into the tray within the housing below. Seems simple enough, right?
True enough, this is a fairly simple design. However, there is some controversy with the way it works. Well, not with the way it works but whether it actually serves the intended function that it purports to serve. Let me explain. There have been several studies from university researchers that attempted to determine whether or not the bug zappers actually attract and kill the intended mosquitoes, biting gnats and flies and other pesky insects. The findings revealed that actually what mosquitoes are attracted to is carbon dioxide, humidity and a type of hormone.
So, it would seem that the bug zapper might not be the most effective means to kill the worst offenders for your outside patio area. This is where the inventors of the mosquito traps come in to play. They have designed several types of what are called mosquito traps. They work by putting out carbon dioxide and water vapor (some also use a mosquito pheromone) to attract the mosquitoes and then utilize a vacuum mechanism to suck them into the trap. This is all run by a propane tank so no electricity is necessary. They have been shown to be a better way to effectively eliminate large numbers of mosquitoes in an evening. Your best bet would be to utilize a bug zapper and a mosquito trap to get the best bang, literally, for your buck.