Traps can be a useful complement for controlling flies in livestock operations. Populations of houseflies, other filth & nuisance flies, face flies, stable flies, tsetse flies, screwworm flies and blowflies can be reduced to some extent using traps.
However, each fly species has a different behavior and is attracted by specific odors, colors or shapes that do not attract other species. This means that traps that work well against one fly species usually do not work at all against other species.
There are numerous commercial traps and much more self-made traps. Commercial traps may not always deliver what they promise. A general weakness of all traps is that their efficacy is rather unreliable because it often depends on variable factors that cannot be controlled by the user such as weather conditions (rain, humidity, temperature, wind, sunlight, etc.), abundance of alternative food or objects that attract the flies, etc.
It is obviously not the same to catch a few flies in the living room, and to catch flies in a feedlot operation or in a poultry house. A flytrap that works well in a given environment may not work at all against the same fly species in a different environment, or during different seasons. Nevertheless it can be worth trying them: there's not a lot at risk. And if it doesn't work, just try another one.
Most traps do not use an insecticide to kill the flies, but may have one. With or without insecticides, traps are especially welcome in dairy and poultry operations where on-animal use of insecticides is undesired because they leave residues in milk or eggs.
Usually traps will not solve a severe fly infestation but can help to reduce the fly populations down to a supportable level. And they make a lot of sense in the context of Integrated Pest Management because they do not select for resistance to insecticides, which is especially relevant for the control of houseflies and blowflies that easily develop resistance.
Traps against specific parasite species
Traps can be helpful for controlling stable flies (Stomoxys calcitrans) in dairy, pig and poultry operations. Best results have been obtained with translucent glass fiber panels covered with an adhesive glue, with electrocuting screens baited with CO2, or with fluorescent light.
Traps have also been useful to keep tsetse fly (Glossina spp.) populations at low levels or as barriers against re-infestation of areas already free of flies. Their efficacy depends a lot on size, shape, color and placement. Results are improved by adding specific attractants (e.g. acetone, cattle urine, etc.)
Face fly (Musca autumnalis) populations can also be reduced with suitable traps. Panels or various materials (wood, glass fiber, etc.) painted white and covered with and adhesive glue can make a good job. Together with chemical control they allow sufficient population control.
Especially numerous and diverse are the traps against houseflies (Musca domestica). Self-made traps can be surprisingly effective. Among the cheapest and more efficient ones for indoor use are the traditional paper-roll glue traps.
Traps with insecticides have also been used against screwworm flies (Cochliomyia hominivorax) as a complement in areas with eradication programs using the sterile-male technique.
There are also commercial traps to catch blowflies (Lucilia spp.) where blowfly strike is a major pest.
Traps can also reduce red poultry mite (Dermanyssus gallinae) populations. The traps take advantage of the fact that these mites leave the birds during the day to rest in their hiding places. Putting such artificial hiding places impregnated with acaricides between the birdcages can kill a lot of mites. Such traps can be e.g. ripped cardboard rolls or plastic tubes.
There are no effective traps against most other external parasites of livestock and pets such as mites, ticks, lice, mosquitoes, fleas, etc. There are traps that will catch some fleas, or some ticks, etc. But they will not solve any flea or tick problem, neither at home, nor in any livestock operation.