What are Head Lice?
Anatomy of the Adult Head Louse
The morphology of the human head louse, Pediculus humanus capitis, was described many years ago using light microscopy. However, electron microscopy allows us to look in more detail at the anatomy. Since our primary interest is in control of the beast, our studies have focussed on organs that enable the louse to make an honest living on human heads. This poster demonstrates some of the surface features of the head louse as seen using scanning electron microscopy.
» Anatomy of the Adult Louse Professor Rick Speare 1998
Head Louse Eggs
Head lice eggs occur in three states:
Being able to identify the state of the egg is important. Hatched and dead eggs are historical evidence of infection.
How do I tell the state of the egg?
Check the following:
- The shape in profile:
- Hatched eggs have no operculum and look like a boiled egg with the top cut off.
- The overall shape:
- Dead eggs collapse in on themselves and the sides are crumpled.
- The colour:
- Live eggs are brown; hatched eggs are pale; dead eggs are brown.
- The pressure inside the egg:
- Live eggs "pop" when squashed between the nails; dead eggs and hatched eggs don't.
The following photographs of head lice eggs have been made using a scanning electron microscope (SEM). The SEM is great for showing details of eggs, but the pictures are in black and white only.
Live Egg
The complete egg consists of a tube which encircles the hair shaft with the egg attached to the end furtherest from the scalp.
Note the operculum forming a lid on the top of the egg. To hatch the operculum opens.
Live eggs have curved walls.
An unhatched egg has the operculum in place
Dead Egg
Dead eggs have the operculum in place, but the sides of the egg have collapsed inwards.
Probably a live embryo is needed to maintain pressure in the egg, and when the embryo dies pressure falls and the atmospheric pressure forces the walls in.
Hatched Egg
Hatched eggs have lost the operculum, and have a flat top in profile.
Remember:
- live eggs = active infection and an infection risk
- dead eggs only = inactive infection; no infection risk
- hatched eggs only = inactive infection; no infection risk
| Myth | Fact |
|---|---|
| Head Lice can Fly | Head Lice can't Fly |
| Head Lice can Jump | Head Lice can't Jump |
| Head lice only like clean hair | Head Lice like any kind of hair; short, long, dirty or clean. They're not fussy |
| Head Lice infections are seasonal | Head Lice are not seasonal |
| Head Lice dont survive on bedding | Head Lice can survive on bedding from a few to 24 hours |