As I was sorting through some pictures for a lecture I’m giving (brownfield ecology, no lice there), I came across several close-ups of head lice I’d taken when we had an infestation some years ago. The nymphs were really too tiny, even for a macro lens, so I’d kept an adult alive in a small glass tube. A twist of damp tissue prevented it drying out, and I kept it in my trouser pocket to keep it safe and warm.
Plonking it down onto a piece of art paper made the right background in terms of colour balance, but the louse was lost against the flatness and struggled to move. It did not look right. Then I remembered the clippings from the kids’ haircuts a few days earlier. We’d thrown them out into the garden. I don’t know, something to do with improving the tilth of the soil maybe. Anyway, the cuttings were still there and I rescued some sprigs, scattered them on the paper and released the louse.
It was remarkably active, considering it had not eaten for several hours; but I put this down to the fact that I had been keeping it in safe and humane conditions. It shot off across the strands at top speed. From memory, I’m guessing it moved at about 2 cm/sec. This was enough to make it quite interesting trying to get the thing in focus as I chased it back and forth across the jumbled strands. It also reminded me why head lice are so difficult to spot on a cursory examination of the dry scalp, and how easily they can scramble over from one victim to another.
What I had in my favour, though, was the fact that the head louse never once let go of the hairs. It ran backwards and forwards, up and down, left and right, exploring every inch of its manufactured backdrop, but it had nowhere else to go; it was trapped. Because, of course, for a louse, letting go is suicide.
Head lice are tiny compared to humans, they are perhaps one hundred millionth the size of their host. If they let go for an instant, they will get injured, or they will get lost. Either way, they will be dead. Head lice do not wander off across the pillow looking for another head to invade, nor do they sit on chair backs, or shoulders, hoping for another hairy human to stroll past so that they can scramble aboard. Within minutes they will start to cool down, and dehydrate. Their body movements will slow, their internal metabolism will start to fail and all the complex physiological workings of their bodies will start to corrupt. After a couple of hours away from its warm moist scalp home, the louse is beyond recovery; its legs may still twitch, but they are its last desperate gropings. No, if a louse lets go, it is as good as dead.