‘Twas the night before Christmas and all through the house,
not a creature was stirring, except the odd louse.
A few days before the end of school, we received a notice about head lice. It got me wondering how these creatures have managed to survive in this sterilized world of ours. I decided to research the life cycle of a head louse. Her scientific name is Pediculus humanus capitis, but she goes by Harriet.
"We head lice don't transmit diseases like body lice," says Harriet. We are close relatives, but are smaller, eat more often and don't survive for more than a day away from the scalp of our nice, warm host."
Harriet is a full-grown female, about the size of a sesame seed. Her host came from a place where most of the people had dark hair, so Harriet has more pigment than head lice would have from places where most people had light-coloured hair.
"But I like all kinds of people," she says.
Harriet clings to the hairs of her host with the claws she has at the ends of her six legs. She is not much of a jumper and does not have wings to fly, but when necessary, she says, "I can get around well enough."
Every few hours she sticks her pointy mouth into a suitable vein to suck the nutritious warm blood.
"If I ever fell off my host, I wouldn't last long," she says.
Harriet recalls the first time a male came calling. "We're bigger than boys and we outnumber them, but they sure are enthusiastic!"
Mating takes about half an hour and shortly after that she is ready to lay some eggs.
She might have been happy to spend her days on the same host, but when another patch of hair collided with her host’s, she crawled over for a change of scenery.
"I don't care how clean or messy the hair is," she says. "But maybe folks who don't care for their hair won't notice me as soon."
Harriet laid each of her half a dozen, poppy-seed sized eggs, near the base of a hair shaft with waterproof glue. "People usually think they're just dandruff, sand or maybe a flake of hairspray," she says.
Nymphs hatch in about ten days. The empty eggs are called nits, although it’s hard to tell by eye if the eggs are empty. The eggs remain attached to each hair as it grows and after the nymphs are long gone. If you find a nit more than about a centimetre from the root, it has probably hatched or is dead.
Like other insects, each nymph moults its skin to get bigger. "It's inconvenient, but that's evolution for you," says Harriet. In about three moults, which takes about twelve days, the nymph is an adult and ready for action.
If you have any "lousy" stories to share, go ahead. I won't nitpick.