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History of insect light traps

Updated: Mar 13

Note: In this article, we use the phrase insect light traps (ILTs) primarily to refer to traps used by the pest control industry for monitoring houseflies and other filth flies.

The ILTs used in fly monitoring are mainly of two types: the zappers or bug zappers or fly-killers or flying-insect-killers, which kill insects by electrocution, and flycatchers, in which the traps’ glueboards capture flying insects. However, even fly catchers kill insects they trap, as the insects they trap die of dehydration.

Some ILTs also catch other insects like nocturnal moths and stored-product insect pests.

Our article’s focus is on ILTs for fly monitoring and control.

Insect Light Traps

Insect light traps (ILTs) during the nineteenth and early twentieth centuries:

ILTs have a long history dating back to the late nineteenth century when early inventors designed these devices to capture and study insects rather than to control their population.

The US Patent and Trademark Office (USPTO) granted the first patent for an ILT in 1877 to William L. Saunders, who designed a device that used a combination of heat and light to attract insects.

The November 1911 issue of the American Popular Mechanics magazine carried the design of a fly trap resembling modern fly zappers by two unknown Colorado residents from Denver. That trap had incandescent bulbs, a high voltage grid to kill insects, and provision for meat as bait, but its high cost deterred its adoption as a popular choice in fly control.

The USPTO granted the first bug zapper patent in 1932 to William M. Frost. In 1934, William Brodbeck Herms of the University of California at Berkeley introduced an electronic insect killer, leading to the future development of bug zappers.

Adding UV-A to light source for attracting houseflies: In the early twentieth century, pest controllers began using ILTs for fly control, and UV-A light became popular to attract insects.

In the twentieth century, ILTs underwent several significant developments with the use of UV-A light as a means of attracting insects.

In the early era of ILT evolution, trap developers focused on attracting various insects using their devices.

Before the introduction of UV-A light, ILTs mainly relied on heat and visible light to attract insects.

UV-A light allowed ILTs to be more effective at attracting a wider range of insects and made it possible to also attract nocturnal insects or those active at night.

The commercially available ILTs now rely on blue light (visible to humans) and UV-A light in the spectrum 300-400 nanometres (not visible to humans).

Within the UV-A spectrum, 350-370 nanometres wavelengths elicit the most response from houseflies.

Another major development in ILTs was using insecticides to kill captured insects in agricultural and outdoor applications. Before the introduction of insecticides, ILTs were primarily used to capture and study insects rather than to control their population.

The use of insecticides allowed ILTs to be used as a tool for pest control, greatly increasing their effectiveness at reducing the population of nuisance insects in farms and outdoors.

In the latter half of the twentieth century, ILTs became more portable and easier to use with the introduction of battery-powered and handheld models. The availability of portable ILTs made it possible for individuals to use ILTs in various settings, including in their homes and travel. Handheld racquet-shaped ILTs are currently popular for killing houseflies and mosquitoes at homes and businesses.

Fluorescent tubes were initially used as the source of UV-A light, but from the start of the twenty-first century, many manufacturers have switched to UV-A Light Emitting Diodes (LEDs). The switch from fluorescent tubes to LEDs mirrors the change in electronics in which homes and businesses have switched to LEDs for lighting.

What is an Insectocutor?

The word “insectocutor” is a combination of the words “insect” and “executor,” and it refers to a device to kill insects by electrocution.

The term “insectocutor” describe an ILT that uses an electrical or mechanical means to kill insects and is another name for zapper or bug zapper.

A Georgian company in the United States of America owns the “Insectocutor” trademark for its products, and its website is

However, it is common in the control industry for customers to refer to bug zappers of other brands as electrocutors, though only one company owns that brand.

How does an insectocutor work?

An interlocutor-type uses blue and UV-A light to attract insects and kills them mechanically or electrically.

The trap is equipped with a light source that emits UV-A light attractive to many insects.

Insects are attracted to the UV-A light in the trap and fly toward it.

As the insects approach the light source, they pass through a grid or screen charged with electricity. The electricity in the grid or screen kills the insects upon contact.

The dead insects are collected in a tray at the bottom of the trap or fall to the ground.

Insectocutor-type insect light traps are commonly used to control the population of primarily nuisance insects such as flies and moths to a lesser extent. They are popular in commercial settings, such as restaurants and food processing facilities, and residential settings, such as homes.

Why must you not use insectocutors near open food?

When a bug zapper electrocutes insects, the device releases a cloud of insect parts that can travel several meters from the device. Such insect spread by bug zappers has led the US Food and Drug Administration to recommend that a food manufacturer not install a bug zapper above food preparation areas.

The research on ILTs generating a cloud of insect parts is inconclusive, with some ILT manufacturers arguing that the evidence for such a phenomenon is limited. However, as the electrocution of an insect may lead to its disintegration, an ILT catch tray is likely to accumulate minute insect debris. In addition, there are chances of insect body parts in the ILT catch tray mixing with the air if there are strong air currents in the space in which the ILT is present.

A second disadvantage of zappers is their sound while electrocuting an insect. Also, the electrical grids of zappers sometimes accumulate dead insects and appear inappropriate in a business setting.

The above disadvantages of zappers led to the development of flycatchers.

How does a flycatcher work?

As fly-catchers trap insects on glue and do not lead to the disintegration of insects and the introduction of trapped insect parts into the air, they are a better option than bug zappers in the food industry and food businesses.

Like a zapper, a flycatcher also has a light source that emits blue and UV-A light. Until recently, bug zappers used fluorescent tubes for a light source, whereas several manufacturers have introduced flycatchers with UV emitting Light emitting diodes (LEDs).

Three generations of ILTs: Over a century, ILTs have evolved from zappers to LED-based devices.

In their first generation, insect electrocuting ILTs helped control flying insects. These first-generation devices lasted for a very long time and are popular even now across the globe.

The second generation of ILTs were the flycatchers that noiselessly killed insects, with some even discreetly trapping insects without making them visible to the trap viewers.

The first- and second-generation ILTs relied on UV fluorescent tubes that emitted blue and UV-A light. In addition, manufacturers sold shatter-proof UV fluorescent tubes for special applications like glass-free areas of the food industry.

The dawn of the twenty-first century has contributed to the third generation of ILTs, which rely on UV LEDs. UV LED-based ILTs are available as both zappers and flycatchers though the latter variety is more common UV LED traps.


Insect light traps are an important tool in the management of filth flies. When used in sufficient numbers and placed appropriately, they help monitor filth fly populations. In addition, ILTs check flying insects in businesses like food factories, restaurants, retail stores, and many establishments that look for effective fly control and a fly-free environment.

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