United States Department of Agriculture
Agricultural Research Administration
Bureau of Fitomology. and Plant Quarantine
CONTROL OF HUMAN LICE
By Gaines W. Eddy and RaymLnd C. Bushland
Division of Insects Affecting man and Animals
Three kinds of licoe attack man--the body louse (Pediculus humanus
orporis Deg.), the head louse (P. humanus humanus L.), and the crab or
pubic louse (Phthirus pubis (L.)). These lioe are world-wide in their
distribution and all are found in the United States.
From a medical viewpoint the body louse is most important, because
in many parts of the world it serves as a vector of diseases, the most
serious being epidemic typhus. Louse-borne diseases are extremely rare
in the United States and, as infestations of the body louse in this
oVptry are usually limited to vagrants, it causes less domestic con-
cern than do head and crab lice. Head lice have been proved capable
of transmitting typhus under experimental conditions, and therefore
are important from a health standpoint. Crab lice are not known to
The head louse apd the body louse are similar in appearance, the
varieties being distinguished only by their location on the host. An
adult body louse (fig. 1) is grayish in color and about one-fourth inch
long; the immLature stages, or nymphs, are smaller, but even newly hatched
lice are visible to the naked eye. A crab louse (fig. 2) is shorter and
much flatter and broader than a body louse. Its orablike shape accounts
for its conmon name.
The eggs, or nits, of human lice are all similar in appearance.
They are whitish in color, and are often more noticeable than the lice.
The presence of eggs is frequently used as an index of infestation when
examinations are made by doctors and nurses.
The life cycles of all three kinds of lice are similar. Ordinarily
egp hatch in about 8 days after they are laid, but eggs somewhat re-
avd from the body develop more slowly at lower temperatures and
incubation "**times requires 2 weeks. Head and body lice spend about
9 days in the iuphal stages., molting (shedding their skins) three times
as they grow to adults. Crab lice develop more slowly than do the other
species. The feales begin laying eggs about 1 day after they have
emerged as adults. A female louse may live as long as a month, laying
4 or 6 eegs eaeh day.
Immature lice usually stay close to the skin.. ?'o-r wriuh they
suck blood, whereAs sexually mature lice ari viC.or mvi ,rto;z,'. Fully
fed, mated females frequently wander about on th. i..'o_..-.g hd do
not seek the akin again until they become hungry. When pecple are
closely associated in situations such as are common in aohools,
barracks, or public conveyances, this habit of the 11i6oe makes for
a rapid spread of infestations.
The body louse lives in the clothing and visits the eklr several
times daily tor feed. The undergarments are most heavily irj ed,
but some lice can usually be found in thb outer olothinp, Ordinarily
the eggs are deposited exclusively on the clothing, thi seams and
folds being preferred. The eggs are usually glued to fibers of the
cloth, but sometimes they are fastened to hairs on the body.
Persistent infestations by the body louse are always associated
with poor sanitation. Control of this insect among civilians is best
accomplished by providing adequate laundry facilities and sufficient
clothing for a weekly change. Either washing in hot w'jGer or dry
cleaning infested garments kills all stages of lice. If all indi-
viduals change to clean clothing once a week, complete control is
assured. Because the body louse lives in the clothing rather than
on the body, this insect is easier to control than are the head louse
and the crab louse.
If some member of an average American' family should hspen to
become infested with body lice, no special procedh-re is %,,.-*zry
to protect the family if the infested person follows the di.reqtions
given above. If, as rarely happens, a few lice or eggs on the indi-
vidual's body should escape immediate destruction, the-,y canot survive
to build up an infestation in a home where ordinary lean Iners is
Eradication of the body louse from any group of people is now
practicable because of the development of insecticides possessing
residual action. One of the most satisfactory materials is a louse
powder consisting of 10 percent of DDT in pyrophyllite or tale, which
was developed at the Orlando, Fla., laboratory of the Bura.- of
Entomology and Plant Quarantine. One ounce of the powder should be
applied over the inner surface of underclothing, and an additio:,;l
1/2 to lo amoe to the seams of tile outer garments. Underwear thoroughly
treated in this way continues to kill lice for about a ir-.-ith's wearing
thereafter. When the DDT powder is properly applied to the clothing
of all individuals in an infested community, a single application will
eradicate the lice.
DDT louse powder can be effectively applied with any shaker type
of container, but laoge groups of people oan be more rapidly oad effi-
ciently treated by delousing crews using standard insctloide dusters.
The Arny fAnd that either hand-operated or power dusters gave good
results and that for such treatment it was not necessary for civilians
tc remove their ciothlng. The nozzle of the duster should be inserted
thro'h orrni-res in the clothing and the powder applied to the skin and
between players of olbthing. When mechanical equipment is used, at least
2 ounces of powder should be applied to each person being treated. If
only a few individuals are to be treated, a satisfactory duster oan be
made from a small jar or can having a metal -id by punching a few holes
in the over.
The use of insecticides is essential for the control of head lioe,
because these insects can withstand frequent shampooing with soap and
water, and it is almost impossible to remove all lIce and eggs by combing
and brushing the hair.
The 10-percent DDT powder is also effective against the head louse,
but because the residue may be visible in the hair a liquid material
known as the NBIN formula, which was also developed at the Orlando
laboratory, is preferred. If the DDT powder is used, it should be
applied either with a mechanical duster or with the shaker type of
container, the method of application depending somewhat on the number
of persons to be treated. The dust should always be thoroughly applied.
Since DDT does not affect the eggs, the powder should not be
washed from the hair for at least 10 days after treatment. If left
in the hair, the powder will kill young lice as they hatch from the
eggs. If an individual user prefers to wash his hair on the day after
treatment, a second application should be made 8 to 10 days after the
Although the NBI3 formula was developed during the war for use
against the body louse in conjunction with certain other control measures,
it should find greater use in peacetime against the head and crab louse.
The formula may be prepared in concentrated form and diluted with water
as needed. The NBIN concentrate consists of the following ingredients:
Percent by weight
Benzyl benzoate ...... . . . 68
Sorbitan monooleate polyoxyalkylene ether 14
derivative (Tween 80) . . . . .
Benzoeaine .. . . . . 12
DDT . . . ... .. . . .*. 6
To prepare an emulsion, 1 part of the concentrate should be diluted
with 5 parts of water. This mixture should be shaken thoroughly before
it is used. The method of applying the material is not so important
as doing a thorough job. The eggs must be contacted to be killed.
To make sure that this is done the hair should be wet, or at least
moistened throughout. Combine the hair following application tends
to insure a more even distribution of the treatment.
If properly applied, this material will kill all lice and eggs
present in the hair, and the residual effect will last for 2 weeks or
more. Even though all the lice and eggs in the hair are killed, there
may be live lice or viable eggs present in the clothing, headwear, or
Ehbjut the home which may cause a reinfestation if the hair is washed
too soon after treatment. To make fairly certain that lice are com-
pletely eradicated, the material should be allowed to remain in the
hair for at least 8 to 10 days. The treatment can be used effectively
as a prophylactic if an application is made every 2 or 3 weeks.
Other remedies, such as larkspur lotion and kerosene in either
vinegar or olive oil, and derris powders and lotions, have been widely
used against head lice. These materials are not ovicidal and do not
have lorn,-lasting properties; therefore, two or more treatments are
required. They are not recommended unless the DDT or th4 I.BIN formula
is not available,
Sanitation is much less important in the prevention and control
of the crab louse than it is for the body louse. The crab louse lives
in the hairs of the body rather than in the clothing, and therefore re-
mov'nr and disinfesting the garments will not free the person of lice;
it is necessary to use insecticides.
Crab lice can be conveniently and effectively controlled with two
treatments of the 10-percent DDT powder. The second application should
be made about 8 to 10 days after the first. All hairy portions of the
body, including the arms, armpits, chest, the pubic and perineal region,
and the legs, should be thoroughly dusted And the material rubbed in
with the fingers. The user should not bathe for at least 24 hours after
applying the treatment.
The NBIN formula is also effective against the crab louse. A single
application has been found to eradicate an infestation. This material
should also be applied thoroughly to all hairy parts of the body and
rubbed in well. Application may be made with any absorbent material
or by hand. If large numbers of individuals are to be treated, a
sprayer with a paint-spray nozzle may be found convenient. The treat-
ment should be allowed to remain on the body at least 24 hours to
prevent a possible reinfestation from lice in the bedding or other
Several other remedies have been used against crab lice in the
past, including blue ointment, kerosene in vinegar or olive oil, and
derris and larkspur lotions. These materials are inferior to the DDT
powder or the NBIN formula and are no longer recommended. Derris powder
or preparations containing kerosene are irritating to the tender parts
of the body and should not be used in orab louse control.
UNIVERSITY OF FLORIDA
3 1262 09238 7280