Sheep farming

Sheep Lice: The chewing insect affecting your flock

Lice are dependent on a host for their survival. When your sheep become the host, lice can spread quickly and rapidly between them. They not only irritate a sheep’s skin and potentially lead to weight loss, but also reduce the value of the wool. If you want to successfully treat them, accurate diagnosis is vital.


Lice Damage Profits

Chewing lice feed on a sheep’s skin debris in the wool. This damages the hide and the fleece, so much so that the wool can decrease in value by up to 80%1.

Sheep Lice 1Image taken from Department of Agriculture and Food [Aus]

Additionally, the irritation caused by lice biting and chewing can reduce weight gain in sheep, which obviously makes them and the farm less profitable.

When large numbers of sheep are suffering, it’s a sign there is potentially a bigger welfare problem. If sheep are not in good health, their vulnerability is exploited by lice, and thus, the lice population grows faster.

Signs of Lice

If sheep are rubbing against trees or fences and biting at their skin, it’s a sign of irritation. This could be due to an infestation of lice but it could also be sheep scab. Lice thrive during the late autumn and winter period, much like the scab mite. So, if the temperature and conditions are right, it’s time to investigate which is the cause.

Identification is Key

Lice are small insects and often visible to the naked eye, scab mites however are much smaller and require a microscope for identification, there is also the possibility of both parasites being present on some sheep. Generally there are two types of lice:

– Blood-sucking

– Chewing/biting

Chewing lice are by far the most common in the UK.  They have a life cycle of five weeks: one to two weeks for larvae to develop into nymphs and only three weeks or less to then become adults.

Lice are photophobic (avoid light) and will often scurry off if you part the fleece. To be sure lice are the issue, ask your vet for assistance and, if needs be, they can take skin and wool samples from the sheep. These can be used to determine if it is lice or sheep scab in order to correctly target the treatment.



Shearing sheep will remove the majority of lice; they subsequently die since they can’t survive away from a host. Once sheared, treat effectively according to the data sheet:

Treatment involves the use of pour-on or spot-on synthetic pyrethroid preparations or organophosphate dips.

– Fly and Lice Spot OnTM is effective against Lice, Ticks and Blowfly Strike, in a simple small dose spot on without requiring a vet assessment of the stock.

Sheep Lice: Fly and Lice Spot On

– DYSECTTM Sheep Pour On in a single treatment will normally kill all lice, with the benefit of 8-10 weeks  fly cover and 8 -12 weeks tick protection.   

Sheep Lice: DYSECT 

You must be absolutely sure lice are present before you give treatment. If the problem is sheep scab and not lice, offering lice treatments will delay your success and incur greater treatment costs.

Alongside medical treatments, good animal husbandry is also vital.  It’s helpful to know how lice operate to avoid inadvertently taking action that encourages them to populate.



1. Sheep Health and Welfare Group Report (2016)

DYSECT SHEEP POUR-ON 12.5 G/L POUR-ON SOLUTION contains alphacypermethrin. POM-VPS FLY & LICE SPOT ON contains deltamethrin. POM-VPS For further information please see the product’s SPC or contact Zoetis UK Limited, Walton Oaks, Dorking Road, Tadworth, Surrey KT20 7NS. Customer Support: 0845 300 8034. Use medicines responsibly ( Date of preparation: September 2016.