Haematopinus suis
The only species of lice found on swine. It's one of the largest lice, some females being up to 1/4 inch long. Hog lice are ectoparasites, sucking blood and causing skin irritation. In young pigs, a large number of lice may cause death from anemia.
Diagnosis
If your pig had red, irritated skin, is spending an unusual amount of time scratching itself (by rubbing up against things), and has small black dots, particularly around the irritated areas, then you may have lice. If you look closely at a black dot, you will should see a small head, six legs along the thorax, and an enlarged abdomen. (If it has eight legs and no thorax, it's a mite or tick).
Treatment
In the past, dipping the pigs in crude oil was a common treatment. These days, you usually spray them with pesticide -- being very careful which pesticide you use. All of your pigs will have to be treated, and some pesticides are not safe for young pigs (piglets younger than 3 months are especially at risk). Sows should be treated at least 40 days before farrowing, and boars should be treated before breeding. You should also do a follow-up spraying about ten days after the original. Always follow the directions given when using a pesticide on an animal (or anywhere else, for that matter).
Life Cycle
(Finally, we get to learn something about the louse itself).
Hog lice spend all their lives on hogs. An adult female louse will lay up to 90 eggs during her life time, attaching them individually to hairs. These are nits, and are most often found on the abdominal hairs of the pig. The female lays about 3-6 eggs a day, for about 25 days.
In about 12-20 days, the eggs hatch, and the young lice (nymphs) look for tender skin, or better yet, abrasions caused by the pig's scratching. A favourite spot is the interior of the ear, particularly in cold weather. The lice do not stay in one spot, but detach after each feeding and wander around the pig (this is part of why they spread through populations so quickly). In about 10-12 days the lice mature, and a couple days later the female will start producing eggs, starting the cycle again.
The average life span is 35 days. Nearly all infections come from pigs touching pigs -- although if a louse falls off its host, it can live for 2-3 days before dying.