Summary
The Australian sheep blowflies, Lucilia cuprina, is a significant parasite for sheep producers as it is the ectoparasite responsible for fly strike. If you haven’t seen (or smelt) it before, fly strike is a nasty condition where flies lay eggs on the sheep’s skin, the emerging maggots then feed on flesh and cause severe irritation, infection, suffering, and often death.
Metallic green to bronze in colour, the blowflies have red eyes, clear wings and are 6-10mm in length. A single female can lay up to 250 eggs in one sitting and up to 1,000 to 2,000 in her lifetime. These eggs hatch within 24 hours, and the larvae feed on the flesh of the sheep resulting in severe infections, suffering and often death if left untreated.
Lifecycle of Sheep Blowflies
- Adult flies lay 250 eggs on a sheep at one time, often multiple times, and 2,000 in their short lifetime. Attracted to warm, moist conditions, they’re usually laid in wounds, soiled areas, or skin founds, typically around the breech or shoulders.
- Eggs hatch within 8 to 24 hours, depending on temperature and moisture levels.
- Fresh larvae (maggots) feed on skin secretions and begin to invade living tissue. Within 3-5 days, the maggots grow rapidly and progress through 3 larval stages. Constantly feeding on the flesh of the sheep, extensive tissue damage (flystrike) occurs within this short time frame.
- Fed maggots drop to the ground to pupate.
- These maggots burrow into the ground, forming hard pupal cases. This stage lasts for 1 to 2 weeks in ideal conditions, or longer in the cooler winter.
- The adult blowfly emerges and is mature to reproduce within a few days. This whole cycle can be completed in as little as 2-3 weeks in the spring or summer.
Risk Factors for Attracting Sheep Blowflies
- Soiled fleece, typically around the crutch
- Wrinkled and loose skin
- Open wounds: marking, shearing cuts, etc.
- Warm & humid climatic conditions (spring to summer)
Signs of Infection
- EARLY SIGNS
- Restlessness and/or Irritation
- Biting or stamping hind legs
- Rubbing
- Isolation from the flock
- Dullness or decreased grazing
- PROGRESSIVE SIGNS
- Discoloured or damp wool (breech, shoulders, poll)
- Foul smell (bacteria breaking down the tissue)
- Wool loss and staining (brownish, clumped)
- Maggots seen with bare eyes (ranging from 2 to 10mm in length depending on the age of the larvae)
- Inflamed or raw skin around infected areas
- SEVERE SIGNS
- Lethargic and depressed stock
- Anorexia, weight loss
- Lying down and unwilling to move
- Death in cases where infection is untreated
Prevention & Treatment
Management Strategies: reducing the likelihood of flystrike from occurring can be achieved with crutching & shearing to reduce wool cover and moist, dirty soiled dags that attracts flies. Also timing these events before fly season for maximum benefit so that stock are least likely to be targeted by egg laying blowflies. Breeding for resistance and selecting sheep with cleaner breeches and less wrinkle, particularly in merinos, is also beneficial for reducing flystrike prevalence and likelihood.
Chemical prevention: a long-acting insect growth regulator (such as Vetmec Strikemaster Extra) is an excellent prevention method against flystrike. It works by preventing the maggot larvae from moulting, which stops their growth before they begin feeding on flesh.
Effective products for flystrike prevention
Vetmec Strikemaster EXTRA Spray On Blowfly Treatment provides 200-day protection against body, breech and poll strike and it may be used off shears or in sheep with any length of wool.
Vetmec Strikemaster EXTRA Spray On Blowfly Treatment also protects mulesing and marking wounds on lambs against fly strike during the wound healing process.
References