Crab louse, Pthirus pubis, the most embarrassing insect in the world.

On holiday visiting friends in the USA many years ago, my host suddenly appeared very agitated one morning and demanded, in a hushed whisper, something along the lines of “What are these?”, thrusting into my hand a strip of sellotape folded over onto itself. Stuck inside it were some minute grey insects about 2 mm long. My near eye-sight was better then and even without the use of a hand lens I could immediately see that they were crab lice. And, bluntly, I told him so. Oh dear. Never was there a blunter instrument used to deliver such a blow.

Unfortunately, in my objective scientific detachment I had forgotten a very important fact: in polite society, Pthirus pubis is perhaps the most embarrassing insect in the world. These are not nice lice. We don’t much like to talk about them. Incidentally, I like the fact that this beast’s name is coined from an ancient Greek word for louse ‘phtheir’. I don’t think it’s hard to guess how the Greeks came up with such a word. When said with a slight lisp and a nasal sneer it makes a suitably derisory sound, just right for such a revolting parasite — phtheir.

But from this same word we also get the wonderful-sounding job title phthirapterist — someone who studies lice. I always thought claiming to be an entomologist was a pretty cool ice-breaker at cocktail parties, but “Yeah, hi, I’m a…phthirapterist” is not to be sneered at, let alone lisped at.

Anyway, back to the USA and my embarrassed and appalled friend. I was later admonished; couldn’t I have at least said something neutral to him like: “Oh these are interesting, where did you find them?” or “Well, I’ll have to have a look through the lens and check a few reference books.” But, no, I came straight out with it: “You’ve got crabs”. Needless to say, this did not go down very well with his fiancée.

What followed was almighty bloody pandemonium. Beds were stripped, carpets, curtains and furniture were vacuumed, clothes were washed and all visitors were required to administer the appropriate amounts of insecticidal shampoo to nether and other regions of the body for prolonged periods. Come to think of it even the poor dog was probably shampooed too. All this despite my exasperated but quietly muttered protests about personal physical contact, casual sex and puritanical American prudery. We went through the polite motions of disinfection, even though I knew, all along, that it is usually intimate sexual activity that allows these lively critters to move around.

No matter what the graffiti says, on many a public lavatory wall, about standing on the seat, crabs cannot jump ten feet, not even one foot, they can’t jump at all, they crawl, and they’re very good at it. To anyone who’s ever seen a crab louse under the microscope, it’s patently obvious that their claws are perfectly adapted to clinging extremely tightly to their host, and that nothing could induce them to let go, until the precise moment of contact, when another host touches, and they can quickly shuffle across.

After my unnecessary bluntness earlier, I thought it better not to dwell on their precise mode of transmission. And despite the many myths surrounding these curious creatures I restrained my usual exuberant impulse to pontificate. So I let things lie. Or so I thought.

Personal embarrassment moved to farce a few days later. Louse episode put aside, ignored or forgotten, conversation in the car turned to my long-standing interest in insects, and the young son of our host innocently asked some question about how insects grew. I tried to explain how invertebrates moult, by shedding their skins. I started with the usual analogy of a medieval knight being constrained by tight and inflexible metal armour. He was quite absorbed in my description of how the insect’s chitinous armour has to be pulled off whilst a new tough hide is formed underneath and then hardens as the old shell is expelled. I started to take the whole exoskeleton thing personally. I did lots of actions as if I were climbing out from my own shrunken skin or badly fitting suit of armour. I threw in a couple of rusty codpiece jokes and vowed to beat my esquire severely for not helping me properly. I was really getting into my theatrical stride now.

This being a maritime state of the Union I then went on to give the example of edible crabs, knowing full well that everyone within hearing had cracked open their shells to eat crab-meat, and had found the moulted carapaces of shore crabs along the beach. With quite some relish I then moved on and went into the details of how to tell male from female crabs; different kinds of crab; crab behaviour and crab ecology; the biggest and the smallest crabs; land crabs and swimming crabs; fiddler crabs and crabs in other parts of the orchestra.

It was only later, much, much later, I discovered that my partner had been secretly hiding her head in her hands, slumped in the back seat of the car, willing me silently, but insistently, through her pleading but unanswered telepathy: “Don’t mention crabs. Don’t mention crabs. DON’T MENTION CRABS.”