Another plug for
www.headlice.org
This organization was begun a long time ago (actually in 1983) by a group of parents and school/public health nurses who wanted to get
factual information out about head lice. Because lice are hard to get rid of, there is a lot of information out there that is not based on facts.
Here's a link to the
Headlice.org FAQs that will give facts about some of the things people believe.
Here's a
headlice.org page about the louse life cycle, including pictures.
The situation with the OP's DD having no head lice one night and then a whole lot just a little while later sounds very much like a hatching of nits that were on the head. One female louse may lay up to 100 eggs in a 30 day lifespan. If you kill the live adult lice, those eggs will still be alive and will hatch 7-10 days after the egg was laid. If a couple of female lice were laying eggs on the head at the same time, a lot will hatch at the same time. The newly hatched lice look fairly similar to the adult ones - mostly just smaller:
About how long lice will live off the body; they usually do not leave their 'host' willingly because the host's head is warm, the hair protects them and they have a ready source of food. Lice off the body will generally only live for up to 24 hours. Without a blood meal they dehydrate and die.
I had a supervisor in Public Health once who tested it out. Even giving them tender loving care (a test tube with cotton in it) and feeding them from her arm several times

, she was not able to keep any alive for more than 24 hours off the body.
I was not going to let any feed from my arm, but I did keep some nits alive for a while in room temperature conditions (in a test tube with cotton on a hair that had been cut from the head of a child with head lice). I looked at them every day under a microscope and did notice that they were not active inside their egg cases until after they were under the warm microscope light for a while. None ever hatched, though. All of them dehydrated and were no longer alive after about 10-14 days at room temperature. I expect that if had been able to incubate them at
body temperature, they might have hatched, but they still would have died because newly hatched nymphs need a blood meal within a few hours of hatching. I sure was not going to test it out.
