Lice. Little creatures can strike
fear into the hearts of parents and
school administrators around the world
and hundreds of millions of people deal
with lice infestations every year.
But as annoying as they are humans and
lice have shared along itchy history.
They have evolved along with us and they've
come along for the ride as we migrated
around the world they've even affected
the outcomes of our wars. So here are
seven facts about these pests that you
might or might not want to know
depending on how itchy
you are right now. Just like- just talking
about it just talking about it!
There are more than 5,000 species of
lice they are tiny and wingless and they
are experts at feeding on birds and
mammals. And they have to be experts they
are obligate parasites being that their
lifecycle depends on finding a host to
feed on. In general lice can be divided
into two groups: sucking lice which have
special suction mouthparts and chewing
lice which have jaw like mouthparts.
Both types sound pretty gross. Depending
on the feeding mechanism they use
different kinds of lice can infest
lots of different warm-blooded animals
with some lucky exceptions like bats.
Adult lice only live about 30 days. In
that time they mate and the females lay
eggs called nits right at the base of
the hair shaft. These nits hatch in
about a week and become small immature
nymphs which stay attached to the hair
shaft and start feeding on blood from
the skin in about two weeks the nymphs
mature into adult lice and start the
cycle all over again they feed on blood
several times a day.
Nymphs can't live without blood for more
than a few hours and adults die within a
couple of days.
So for lice finding and sticking to a host is key
Luckily out of all of those thousands of
species there are only three types of
lice that are known specifically to
infect humans: head, body, and pubic lice
Head lice or Pediculus Humanus Capitis
are probably the most well-known. They are
common pests but head lice aren't
typically very dangerous they're just
very itchy. Humans can also be infested
with Pthirus Pubis the pubic louse AKA
crabs. The pubic louse is smaller and
rounder with large claws adapted to
attaching to coarser pubic hairs. It can
also infest other parts of the body with
coarse hair like eyelashes and eyebrows.
Like head lice pubic lice don't really
transmitted disease they just cause lots of itching
Then there's body lice
They're so closely related to head lice
that they're considered different types
of the same species but the body lice
can be dangerous. They've been associated
with diseases like Typhus, Trench Fever,
and Louse-born Relapsing Fever because
body lice can carry the bacteria that
cause these diseases and the poop from
an infected louse is contaminated if
human host scratches a bite or even just
has a small cut or scrape the bacteria
in the feces can get into the bloodstream.
Typhus and Louse-Born Relapsing Fever are often fatal.
Trench Fever isn't deadly but it is severe; it
causes very high fevers for days at a
time. Body lice were common in trench
warfare where soldiers were crammed
together in unsanitary conditions and
those lice would spread disease.
Part of the reason Napoleon failed in his
invasion of Russia in the early 1800s eighteen hundreds was that
tens of thousands of his soldiers died
from Typhus spread by lice and the
trench fever was a huge problem during
both world wars. The body lice are the
ones that you probably want to avoid.
The best way to prevent body lice is to
avoid contact with other people who have
it and to wash your clothes and body on
a regular basis. But it turns out that
another way to avoid getting body lice
might be getting head lice. A group of
researchers from Hungary proposed this
idea in 2012 based on the fact that
humans often touch head to express
affection like when you leave your head
against your friends head while you're
taking a photo. Humans do this all the
time but non-human primates don't.
And there's another thing that's unique to
humans too, a separate kinds of lice for
our heads and bodies. The team realized that
there might be a connection between head
touching and lice. There's some evidence
that exposure to body lice can provide
some protection against them.
When a separate group of researchers injected
rabbits with an extract from body lice
fecies the lice had a much harder time
infesting them. They ate much smaller
blood meals laid fewer eggs and fewer of
the eggs that they did lay managed to
hatch and remember head lice are very
closely related to body lice so it's
possible that having a mostly harmless
head lice infestation could provoke
an immune response in humans protecting them
from a much more dangerous body lice
infestation later on If that's true
the Hungarian researchers argue that
affectionate head touching might have
evolved as a way to intentionally
transmit head lice to your friends and
loved ones helping protect them from
body lice and the diseases they carry.
But even though body lice are the bad kind they
can be super useful for researchers
studying human history
It's easy for head lice to attach to
thicker heads of hair but we don't have
much body hair as our early ancestors so
the lice needed a way to get up close
and personal with our bodies and
genetic analysis of head lice and body
lice show they diverged on the
evolutionary tree around 170,000 years ago which means
that's probably when humans started
experimenting with clothing. That makes
sense since the kind of mini ice age
began around a 130,000 to 180,000 years ago so clothing may have
become more of a necessity.
But early humans lost the majority their body hair
around a million years ago so we spent a
lot of time surviving in the wild
without body hair or clothing.
Pubic lice can also tell us something about human
evolution as specifically our ancestors
sex habits since pubic lice are mainly
transmitted through sex. Head and body lice
are super closely related to each other
but pubic lice are much more distantly
related. In fact it's not even the same genus.
In fact it shares a closer ancestry with a
different species Pthirus Gorrilae which
infests gorillas. Now these two species
diverged around 3.3 million years ago
when our Australopithecus afarensis
ancestors were around which means that
at some point Australopithecus and
gorillas were in close enough contact
for gorilla pubic lice to infest our
ancestors possibly sexual contact. But we
know that pubic lice can also be
transmitted by sharing bedding or towels
and so it's possible that Australopithecus
and gorillas were just sharing habitats
and that our ancestors reused nests
where gorillas had slept which would be...
I would... I mean... I understand it's nature
things happen nature but that would be
less disturbing. The genetics of lice
can tell us about the history of human
migration and civilization too, because
when our ancestors left Africa and
spread around the world they brought
lice with them. Nits have been found on
ancient artifacts like pieces of
clothing and personal combs may have
also been found preserved in the bodies
of mummies from as far back as 10,000
years ago. In studying the genetics of
lice from these mummies as well as
modern samples from around the world we can
help track how humans migrated out of
Africa to Asia and the Americas. In a
2013 study for example researchers
looked at lice genes from samples
collected from Asia and North America
Central America and Europe and they
found that lice from Central America had
more of their genome in common with
lice from Asia while lice from North
America where more closely related to
samples from Europe which means that
lice in central america were probably
brought from Asia thousands of years ago
while the most common strains of lice in
North America were spread by European
settlers much more recently so studying
lice can tell us a lot about our
evolutionary history but we're also
having a huge impact on their evolution
keep trying to kill them and they keep
becoming resistant to the treatments we
use. A type of chemical called a pyrethroid
for example used to be great at killing
off insects including lice. But starting
around the 1990s they became
much less effective on lice. The lice had
acquired genetic mutations in a specific
gene that help them survive by reducing
the sensitivity of the nervous system in
response to the insecticide treatment
And when these so-called super lice
survive treatment they breed with each
other and they pass along their
resistance their offspring so you end up
with even more Super lice but there are
other classes of topical insecticide
that do still work effectively benzyl
alcohol for example essentially
suffocates the lice by targeting their
respiratory system so it can have side
effects like skin irritation there's
also spinosad and ivermectin which both
contain compounds that affect the insect
nervous systems but eventually lice
might develop similar genetic resistance
to those drugs too. There are other
effective methods though. One study coated
hair in a skin cleaner specifically
cetaphil and then blow dried it and fill
it hardened into a kind of shrink wrap
coating and left it there for eight hours
The researchers found that the hardened coating
suffocated life with a ninety-five
percent success rate and in clinical
testing heated air from a
specially-designed blow dryer was shown
to kill ninety-eight percent of nits
and eighty percent of live lice. But if all
else fails you can always do what humans
have been doing for thousands of years
take a fine-tooth comb and spend hours
picking out nits and adult lice. Or of
course just give up and shave your head entirely.
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