crab louse

A pubic louse, or crab louse

I became an unwilling expert on pubic lice a couple years ago when I bought “crabs” online at the request of a reporter. Really. It’s a long story, and you can listen to a version of it here; the abridged version is someone calling himself “Lice Lice Baby” claimed he would sell you “Giant Japanese Pubic Lice” as pets.  He re-branded his crab lice as “Seamonkeys in your Pants.”

The French call pubic lice “papillon d’amour”, but for all the happy euphemistic talk about “the ultimate sharing of your love,” crab lice are blood-sucking parasites. At the time, my primary concern was pointing out that deliberately infesting yourself with pubic lice was probably not a very good idea, and a public health risk.

This somehow made me the go-to person online for pubic lice, which is not, frankly, an expertise I particularly aspired to.  I was talking to someone recently about public lice (now a regular occurrence) and I realized that I didn’t know the specific mechanism by which pubic lice suck (aside from the fairly obvious suckage of being infested). I did a little research, and what I found out actually made pubic lice creepier. I did not think that was possible.

One of my primary resources was a paper with this wonderful title:

BURNS D.A. & SIMS T.A. (1988). A closer look at Pthirus pubis, British Journal of Dermatology, 118 (4) 497-503. DOI:

A closer look, indeed! This is a scanning electron micrograph of the sucking end of a crab louse, magnified about 1000 times.

pube lice haustellum

Pthirus pubis is a member of the Order Anoplura or ‘sucking lice’. It is a solenophage (vessel feeder—from the Greek ‘pipe’ + ‘eating’), introducing its mouthparts directly into a blood vessel to withdraw blood. The components of the mouthparts responsible for probing the skin and piercing a blood vessel are kept withdrawn within the head unless the insect is feeding… In the front of the head is a small, snout-like tube, the haustellum, which is soft, eversible, and armed with teeth. Figure 5 shows the haustellum retracted, and the buccal teeth are clearly visible.

But wait! There’s more!

When the louse is about to feed… the buccal teeth rotate outwards. The teeth cut into the epidermis [skin] with a movement compared to that of a rotary saw, and the haustellum is gradually driven into the dermis. It eventually comes to rest with the buccal teeth fully everted, anchoring the mouthparts in the skin….The stylets are advanced into the dermis as a single bundle and probe for a small blood vessel. Once the stylet bundle has pierced a blood vessel feeding begins.  [emphasis mine]

electron micrograph of crab liceEgad.  That little tube? It’s like a hypodermic needle going into one of your blood vessels.

If you haven’t already unconsciously crossed your legs while reading this, this next bit should do the trick. One of the characteristic signs of pubic lice feeding is little blue spots on the skin. It’s a combination of blood leaking out after that mouth-needle is withdrawn and a reaction to the saliva of the louse.  Another symptom of a crab louse infestation is described as “black powder in your underwear.”  That powder is your dried up blood, after the louse has digested it and pooped it out.

I’m not sure that anyone besides me really needed to know this information, but it is a fascinating example of how insect mouth parts have evolved to make them highly successful external parasites!

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Posted by Gwen Pearson

Entomologist. Educator. Writer. NERD.


  1. Thank you to Tommy Leung for catching the hilarious typo ” “black power in your underwear.” Fixed :)

  2. I am not usually grossed out, but now I am. Thanks, I guess.
    I was taught in grad school that the leg spans of lice are a good fit to the density of hairs in their chosen regions of their host species. So the wider leg spans of pubic lice, in comparison to human head lice, is an adaptation to the wider hair spacing in our nether regions. You are welcome.

  3. Ah, Bug Girl, you do so know how to cut to the chase. Once when I was a much younger entomologist a woman far too attractive for me started being attentive. I wasn’t sure if I should run away or close my eyes and surrender, but before I had to make a choice the opportunity came to introduce her to my undergraduate advisor, Professor Don Messersmith. She seemed unduly interested in meeting an entomologist. Dr Messersmith’s parents had been missionaries in China and he was always very reserved, but also very kindly and very much a scientist (loved ceratopogonids). When I introduced the young lady to Dr Messersmith, she pounced and said ‘maybe you can help me, I have these bugs’ and proceeded to yank a fleck from her eyebrow [sic]. Dr Messersmith politely identified her bug as a pubic louse, made an excuse, and left. Reduced from potential lover (and somewhat esteemed student) to pest control advisor, I did what I could to help (if only I had known all the gory details!). Unfortunately, I then became the ‘go to’ person in the dorm for similar infestations (alas, all males). Sic transit gloria mundi.

  4. As a pest controller, my favorite experience with pubic lice is being asked “so when can I have sex again?”

    “You…do realize I’m pest control, right?”

    I should have said never.

  5. wait–they called a PCO for pubic lice? Inquiring minds want to know more!!

  6. It happens. For scabies too. Most people suspect they have bed bugs and then I have to tell them they have other issues and to seek some sort of medical opinion. But, it has never stopped anyone from asking me anyway!

    I am also the front line for meth addict and prescription medication hallucinations. That, is a whole other thing.

  7. […] In case you missed it, pubic lice suck. […]

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