A nit, the egg of the louse, is laid on the shaft of a hair. Nits that come off the hair are harmless and cannot infect a new person.
Nits hatch 7-10 days from when they are laid. When a louse is first hatched it is called a nymph.
The nymphs shed their outer shell (exoskeleton system) three times before the bug is an adult. The nymphs will very rarely leave their host’s head until mature and fertilized.
A female adult only needs to be fertilized one time and is fertile for life.
The female lays her first eggs one or two days after being fertilized. She can lay three to five eggs twice a day for the next 14-16 days. She can lay up to 200 eggs in her lifetime. If a fertilized louse moves onto a new head, the louse may thrive and lay nits almost immediately. She may not survive the blood type of the new host and die leaving behind a few hard to detect viable nits that will hatch to thrive on a new host.