 Lice may reduce host life expectancy if the infestation is heavy , but most seem to have little effect on their host . The habit of dust bathing in domestic hens is probably an attempt by the birds to rid themselves of lice . Lice may transmit microbial diseases and helminth parasites , but most individuals spend their whole life cycle on a single host and are only able to transfer to a new host opportunistically . <unk> lice may reduce the thermoregulation effect of the plumage ; thus heavily infested birds lose more heat than others . Lice infestation is a disadvantage in the context of sexual rivalry . 
