Attract, Trap, and Zap Flying Insects

Using Electronic Insect Light Traps

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Insect light traps (ILTs), also called insect electrocutors or bug zappers, can be very effective in attracting, trapping, and zapping flying insects. But, it is important to realize that that is exactly what the insect light trap is doing: Attracting the insects in order to trap or zap them.

So if you put a trap right on the patio or porch where you are sitting, you are actually going to bring more mosquitoes, flies, and moths to you!

What this means is that a light trap must be correctly placed so that it is not attracting mosquitoes or flies toward people or into a building. This article discusses various forms of "bug lights," proper placement, maintenance, and efficacy.

Types of Insect Light Traps

The basics of any ILT are a light to attract the insects; a "trap" to contain the live, dead or dying insects; and a housing to hold it all together. In some cases, a bait will be used as an additional attractant.

  • Light - An ultraviolet (ULV) light which is attractive to most flying insects.
  • Trap - Some ILTs literally zap, or electrocute, the incoming flies. In these cases, there is often just a raised-edged pan at that bottom of the ILT to hold the dead and dying insects. In other cases, the insects will not be zapped but will be caught on a glue board or glue-strip when they arrive in the lit area.
  • Housing - Any number of variations may be found, depending on the type and the manufacturer. However, most will appear, in one form or another, to be a light within a caged area.
  • Bait - In non-electrocuting, glue board-based ILTs, the glue board will often include an attractant which helps to lure to insect to the glue once it is inside the trap.


Proper placement of ILTs is critical so that invading insects are being attracted to the light; rather than the light attracting insects to invade.

  • Outside - place traps away from the areas in which people will be congregating. If a cook-out is planned on the patio, place the ILT in the yard some distance away. This way insects will be attracted away from the people to the distant light. If the light is placed on the patio, it can compel insects from across the yard to fly over and join the party.
  • Indoors - place ILTs away from sightlines of doors and windows, but close enough to quickly attract any that sneak inside. Once again, if the flying insects can see the light from outside, they can be drawn to and through an opening door or unscreened window.
  • Near food areas - position ILTs so that dead insects cannot fall onto food, food-contact surfaces or utensils. The U.S. Food and Drug Administration (FDA) recommends that ILTs be placed at least five feet away from any exposed food or food-contact surface.
  • Height - there is some controversy over the best height for placement of ILTs, but this is primarily dependent on the insect being targeted. Flying insects have varying flight patterns and heights at which they generally fly. While specifications will vary according to the source, a few general rules of thumb include:
    • Large flies, such as house flies, fly low, so traps should be placed about three to four feet off the ground. (Indoors, however, it can be just as effective to position the traps at higher levels.)
    • Small flies, such as fruit flies, can be best caught at levels of about four to five feet from the floor.
    • For most mosquito species, traps should be hung five to six feet from the ground.


    Whether insects are trapped on a glue board or zapped to fall into a tray, the equipment should be cleaned out regularly. If the trap is indoors, it should be cleaned on a weekly basis. If dead insects are allowed to build up, they can attract secondary, scavenger insects and begin a new infestation.

    If a glue board or glue-strip trap is used, the board or strip should be regularly changed, both to remove dead insects and to maintain efficacy, as dust can gather on the glue and decrease the adhesion.


    Insect light traps can be a very effective form of control of occasionally invading mosquitoes, houseflies, small flies, and moths when placed and used correctly.

    However, the traps cannot be expected to control a serious infestation if conditions exist for the insect to be living and breeding in or around the home, and/or entering the home.

    In such cases, effectiveness will be dependent on finding and eliminating the source of the problem, such as standing water or unsanitary areas; and repairing entry points, such as torn screens, unfitted doors or windows, or cracks and gaps in exterior walls or foundations.