Your Reading List

Nature’s fly control program

Parasitic wasps won’t eliminate flies, but can reduce numbers

With the arrival of spring comes the new crop of flies. Since experiencing fly strike last year, controlling the fly population is more of a priority.

Last summer we began to notice not only were sprays not working as well as they used to, they are getting harder to find. This is due to tighter restrictions on chemicals. The flies are also becoming immune, making chemical control less effective.

Another option is biological control using fly parasites called parasitic wasps. This is not an eradication method, but a process of reducing the fly populations to a manageable level. These fly parasites already live in Canada. We are not introducing a new species by seeding our farms with inoculated fly eggs, we are just boosting their numbers.

Related Articles

Fly parasites, commonly referred to as fly predators, are one of nature’s control methods. Fly parasites are tiny wasps (the size of a fruit fly) that occur naturally, are mainly nocturnal, and do not harm humans, livestock or pets.

While there are other natural predators such as birds and spiders, the fly parasites are unique because they target the developing flies. Under circumstances normally observed in nature, these natural controls keep a balance in the fly population. When humans artificially increase the concentration of animals, we provide an ideal breeding environment for fly reproduction and the natural controls cannot keep up to the fly population explosion.

Parasite mode of action

The parasite females search for a fly pupa and can burrow up to six inches (15 cm) into manure or compost in order to reach the prey. They then deposit their eggs into the fly pupae and the young parasites will consume the fly pupae as nourishment while developing into adult fly parasites. Each female will lay between 50 to 150 eggs depending on the species. These adults emerge fully grown and ready to search out more fly pupae and start the reproductive cycle again. Normally, this cycle takes 18-21 days depending on the species of fly parasite and temperature. The adult fly parasites also consume some of the fly pupae, providing a secondary method of reducing the potential fly population.

Producers have been reporting very good results using predator insects for fly control in many settings. The largest sheep producer in Manitoba has successfully adopted their use. There are also feedlots, dairies and egg producers coming on board and are having a massive reduction in flies. That is not only making their neighbours happy — the less annoyed the livestock is, the higher their production.

A point to remember: a biological program should be started early in the year because it is easier to prevent an increase than to control a well-established fly population. Flies lay more eggs and have shorter life cycles than the fly parasites. If the problem is attacked early, the fly parasites have fewer pupae to attack, therefore they do a better job and fewer pest adults hatch out, resulting in fewer eggs laid.

Reducing fly numbers helps

Some things to keep in mind to help reduce fly reproduction and help out the fly parasites:

  • Flies require a moisture range of 35-70 per cent for successful larval development so keep manure piles as dry or as aerated as possible.
  • Stir lagoons or seed the top crust with fly parasites.
  • Repair all leaking water lines and try to reduce any wet areas, as these are natural fly-breeding grounds.
  • The fly larval developmental cycle is about seven days so the manure should be dried out before that time. In a humid region, it is best to wait until cooler temperatures in the fall before spreading the manure.

The idea is that once released, the predators will keep breeding and eventually keep up with the flies. We would get a shipment monthly during fly season to keep our population high. If we can cut back on the ideal conditions that have been provided for the flies to overtake the natural predators here already that would be very helpful also. The people at have been very helpful at formulating a customized program.

About the author



Stories from our other publications