Answer to Case 701

Answer to the Parasite Case of the Week 701: Female Pthirus pubis, a.k.a, the 'crab' or 'pubic' louse. She is gravid - with 2 eggs! I've seen many female crab lice with eggs, but never one with two eggs at once, so when I came across this specimen, I immediately wanted to share it with you. An anonymous reader commented that "She's very likely to die prematurely from being egg bound, and will suffer from that full feeling."  I thought that was a very interesting (and rather witty) statement. Does anyone know if a female P. pubis with 2 eggs is less likely to survive?

Note that the pubic louse is shaped somewhat like a pelvis - a helpful feature for differentiating it from the head/body louse, which has a much longer body. The pelvis reference is useful since P. pubis is sexually-transmitted. It's also important to note that both the pubic and head/body louse have large raptorial (grasping) claws, but the pubic louse has larger claws on the second and third legs which, in combination with its body shape, make it look particularly crab-like.

As mentioned by Sam, we can tell that this is a female due to the morphology of the posterior end, whereas the male posterior end is more rounded. He also commented that "This louse causes genital crabs. The claws are designed to latch onto the course pubic hairs of the genital area, allowing sexual transmission of this ectoparasite."  Here is a side-by-side comparison of the 2 human lice (Pediculus humanus and Pthirus pubis) for comparison. Also check out Case of the Week 700 for a nice example (and my mascot!) of P. humanus.

Head/body louse (left) and pubic louse (right)

Thank you all for the excellent comments on this case!