[caption id="attachment_135" align="alignleft" width="300" caption="CDC/James Gathany"][/caption]
Head lice that I’ve seen have ranged from pale ivory through a golden – sometimes reddish – brown; magnified, they are transparent. Lice that have fed have a black mass inside – presumably blood in the process of being digested – but are not, themselves, black. There is a colour range, to be sure. But black? A literature search turned up some interesting things:
- Head lice may have a natural way of blending in without actually changing colour. Ibarra and Hall wrote: “Eggs and lice are well camouflaged, reflecting the colour of their surroundings.”
- Newly hatched lice that have not fed are transparent (Meinking) and do not have colour until after they’ve fed.
- Colour that matches the background has been shown to have evolved in other species of lice (Bush et al.). This, however, refers to colour change over generations, not within the life span of a single organism.
The ‘wisdom’ that human head lice change colour depending on the hair colour of the host is oft repeated on websites and in non-academic publications. Published scientific information to back it up, however, appears nonexistent. Similarly, parasitology texts and laboratory identification references do not mention it.
I remain highly skeptical that our head lice can change colour within one generation, or that black head lice actually exist. I conclude that the Chinese remedy called for human head lice that had fed and had blood in their guts.
Bush, Sarah E et al. 2010 “Evolution of Cryptic Coloration in Ectoparasites.” The American Naturalist 176: 4
Hoeppli, R. 1959. Parasites and Parasitic Infections in Early Medicine and Science. Singapore: University of Malaya Press, pg 181.
Ibarra, J., and DM Hall. 1996 “Head Lice in Schoolchildren.” Archives of Disease in Childhood, 75.
Meinking, Terri. 2004 “Clinical Update on Resistance and Treatment of Pediculosis Capitis.” American Journal of Managed Care. 10:9, Sup.