A basic understanding of the biology of lice will assist you in identifying and controlling them.
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A brief description of the lice and their economic effects.
Biology of sheep lice (Bovicola ovis)
Lice, their effects, life cycle, spread sources, their build up and distribution.
Why control sheep lice? Economic effects of lice on production
A description of how lice affect sheep and the associated production costs.
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There are three species of lice that occur on sheep in Australia.
The sheep body louse (Bovicola ovis, formerly called Damalinia ovis) is a pale-yellow insect 1.5 to 2 mm long with brown transverse stripes on the abdomen and a broad, red-brown head (Figure 1). It is a chewing louse and feeds on skin scurf, lipid and sweat gland secretions, superficial skin cells and skin bacteria (Sinclair et al. 1989). Males are smaller than females and have more pointed abdomens.
Sheep are also host to two other species of lice that are both sucking lice, which feed on blood, have long thin heads and appear bluish in colour:
Sheep lice do not breed on animals other than sheep (with the possible exception of goats, in very rare instances). Birds do not carry sheep lice and they do not remain in wool rubbed onto fences, trees or other structures, so these are not sources of infestation.
Infestation with sheep lice can reduce clean wool cut by up to 1 kg per head. Lice also reduce yield because the sheep becomes itchy from the irritation and they will scratch or bite at the fleece causing fleeces to become cotted and yellow, resulting in increased losses during processing.
In New Zealand, sheep lice have been shown to cause a defect in sheep leather known as cockle. This manifests as multiple, sometimes discoloured, lumps visible in sheep leather after processing. Infestation with B. ovis does not affect fibre diameter and, contrary to popular belief, does not cause reduction in body weight.
Temperatures (in the wool where the lice are situated) outside very specific ranges will prevent various stages of louse reproduction from occurring.
A female louse will cement individual eggs to wool fibres, most within 12 mm of the skin; she will lay 1-2 eggs every 3 days and these will hatch 9 or 11 days later. The entire life cycle from egg to egg takes about 34 to 36 days, which includes three nymph (instar) stages.
Lice move to the surface of the fleece when it is shaded and warm. Transfer between animals occurs when sheep are in close contact, such as when they are shedded, held together in yards, or perhaps when feeding or drinking from a trough. Transfer is fastest:
Lice can be found on most woolled areas of sheep, although they are rare on the belly and don’t appear to breed there. They are not evenly spread, but have a clumped or aggregated distribution. At most times of the year densities of lice are highest along the sides and sometimes on the back of sheep. At times, significant numbers of lice can also be found on the head, underlining the importance of thorough coverage when dipping sheep or applying backliners.
After shearing, a greater proportion of the population are found at sites on lower body regions such as under the neck, lower flanks and upper legs and in areas where the wool has not been closely shorn.
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