Human Lice
Only three of the 200 known species of sucking lice
infest humans. They are the head louse, the body louse
and the crab or pubic louse. Sucking lice are
ectoparasites which feed on the blood of their host. They
are flattened dorso-ventrally and their legs are adapted
for clinging to the body hairs of their hosts.
The life cycles of the three human lice are very
similar. The "nits" (eggs) are cemented to hairs (Crab
and head lice) or to fibers and seams of clothing (body
louse). The eggs hatch in 8 to 10 days (at 80-85 degrees
F). Eggs fail to hatch if they are exposed to
temperatures lower than 70 degrees F for 7 to 9 days. The
louse nymphs (immature) feed on the blood of their host
and molt three times before developing into sexually
mature adults. After mating, the females begin to deposit
small numbers of eggs each day for 20 to 30 days. A
female crab louse deposits a total of about 30 nits. Head
lice deposit 50-100 nits and body lice deposit 275-300
nits. The entire life cycle requires 21 to 27 days, and
the adults live for 35 to 40 days.
Body Lice
The body louse is not a common problem in Michigan.
This louse lives in clothing that is in close contact
with the body and they periodically visit the host to
feed. The nits are cemented to the seams and fibers of
the clothing. This louse is mostly a problem in
overcrowded, unsanitary conditions, especially when
clothing is not changed regularly. This louse is
responsible for the transmission of several human
diseases, including epidemic typhus and relapsing fever.
The body louse is nearly identical in appearance to the
more common head louse, but differs in being larger in
size (2-4mm) and uniformly grayish-white in color.
Head Lice
The head louse commonly infests school-aged children,
but is also found on adults. The head louse is 1-2 mm in
length and grayish-white with dark areas along the side
of the abdomen. The nits are firmly attached to the base
of hairs, especially behind the ears and on the back of
the neck. The adult lice may be found in any facial hair,
but they are almost never found below the neck.
Transmission of the lice is by direct contact with
infested persons or by using infested articles (headgear,
combs, brushes, hair rollers, scarves, and in rare
instances upholstered chairs and bedding).
Crab Lice
The crab louse is 0.8 - 1.2 mm in length and has a
distinctive crablike appearance. This louse generally
infests the pubic region, but in some instances may be
found in other areas covered with coarse hairs such as
armpits, beards, and eyebrows. The crab louse is
primarily transmitted by sexual contact, although in rare
instances they may be acquired from loose hairs on toilet
seats and in bedding. The survival time away from the
host is very short for crab lice.
Lice Control
Contrary to popular opinion, anyone can acquire lice
regardless of sex, race, economic status, family
background and personal habits. The control of human lice
begins with two important steps: regular inspections and
proper identification of the louse species involved.
Infestations may be detected by the presence of the
lice themselves or by other signs. Infestations cause
intense itching and subsequent scratching and severe
cases can cause scarred, hardened, pigmented skin
("vagabond's disease"). The fecal pellets from head lice
may be seen on the shoulders, especially if light-colored
clothing is worn. Lice may be detected by the nits
attached to the hairs. However, old nits (hatched) will
remain attached to hairs for a long time, and in fact
they have been found on wigs. Old nits are pale and
papery; new nits are yellow and opaque. Also, since the
hair continues to grow after the eggs hatch the old nits
will tend to be higher on the hair shaft. It is important
to distinguish louse nits from scalp scales and this may
require a magnifying glass.
Consult a physician. Every member of the family
should be treated. Use Kwell 1% shampoo.Baby oil is also
effective. Repeat in 2 weeks if needed. Do not get in
eyes.
Practice proper personal hygiene. Avoid using other
individuals' combs, hats, towels, or hairbrushes. Bedding
and clothing should be changed and washed frequently.
Sanitation of locker rooms, and proper laundering will
help reduce the incidence of lice. Crab louse is usually
transmitted through intimate sexual contact.
For a complete listing of suggested control options
for all home, yard and garden insect pests contact your
local Extension Service, found under local government in
the phone book.
Read and follow instructions on the pesticide label.
Heed all warnings. Check with your physician if you have
any concerns regarding your personal health risk.