Lice

In mediaeval times the sanctity of holy men was enhanced in proportion to their lousiness … Absence of lice from one's body used also to be regarded as a sign of lack of virility, and even today the religion of large numbers of people forbids them to kill a louse though it is permitted to remove one from one's own person and deposit it unharmed on that of a neighbour.
Michael Tweedie, Encyclopedia of Insects
Symbols of manliness, once:
they showed how hairy you were,
how much you could take.
Of saintliness, too—
a hair shirt full of them
maddening the soul heavenwards …
They congregated where men
were men—in war, on shipboard;
thrived in jails
thus being brought to trial—
the judge magically protected
by a nosegay.
Ruthless social critics,
they punish the downtrodden,
expose Romantic self-neglect
worn with a cravat
while dancing in Rimbaud's hair
to joyously shock the bourgeoisie.
A few religious persuasions
suggest proffering a louse
non-violently to your neighbour—
like all good deeds, perhaps
best done on the quiet.
For some they still bode fair fortune:
these purveyors of ship fever,
trench fever, a thousand plagues,
and the myth of their own beneficence.