New Zealand

Fly Strike

Flystrike is the most important ectoparasitic disease of sheep in New Zealand. Three species of blowfly can initiate flystrike in sheep:

  • Lucilia sericata (common green blowfly)
  • Lucilia cuprina (australian green blowfly)
  • Calliphora stygia (brown blowfly)

Chrysomya rufifacies and other Calliphora spp are secondary invaders.

The normal flystrike season occurs from November to March when it is warm and humid. Although this will vary slightly between areas.


Faecal and urine staining around the crutch.

Fleece rot and dermatophilus.


Head injuries in rams.

Wrinkled skin (merino’s).

Infected or open wounds.


Clip off wool immediately around affected area.

Apply insecticide to the struck site and clipped off wool.

Prevention of flystrike is preferable to treatment.


Prevention should cover the total period that flystrike is expected for.

Different types of chemicals should be used for treatment and prevention within a season.

There are 5 separate types of chemicals that can be used to prevent flystrike:

  • Organophosphates (e.g. protamphos).
  • Synthetic Pyrethroids (e.g. cypermethrin).
  • Insect growth regulators (e.g. triflumuron).
  • Insect Development Inhibitors (e.g. dicyclanil).

Methods for application:

  • Jetting wands.
  • Spray races.
  • Backline treatments.
  • Plunge dips.
  • Shower dips.

Both the product used and the method of application will determine the amount of chemical that is successfully applied to the sheep and this in turn determines the length of protection afforded against flystrike.