In his 18th-century poem To a Louse, Scottish poet Robert Burns described the wee insect as: “Ye ugly, creepin, blastit wonner, Detested, shunn’d, by saunt an’ sinner.”
Two hundred and forty years later, it’s fair to say that lice don’t have the best PR. But these mini evolutionary marvels are misunderstood. Sure, they can be parasitic, blood-sucking and itch-inducing. But they can also be plucky, resourceful and fiercely loyal to their hosts.
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Life is all about seizing opportunities. Lice were already taking advantage of theirs around 100 million years ago, when they hitched their fortunes to other animals and made a living by feeding on their bodies.
Today, there are more than 5,000 species of lice, divided into two broad camps. Chewing lice live among the hairs and plumage of their hosts, chomping on skin flakes, feathers and other debris. Sucking lice, by contrast, have evolved specialised mouthparts for piercing the skin and drinking blood. They spend their lives clinging to their hosts and rarely venture far from their food supply.
Contrary to their unsavoury reputation, the vast majority of lice don’t cause disease or bother their hosts that much. Most species are adapted to live on just one species, so their survival depends on keeping that host staying alive.
Of course, there are a few rabble-rousers. Unlike human head and pubic lice, which are irritating but generally harmless, the human body louse can transmit serious diseases, including epidemic typhus and trench fever. And when large numbers of hog lice infest pigs, they can leave their hosts anaemic, itchy and struggling to put on weight.
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But spare a thought for their talents.
It’s a little-known fact that human head lice are expert glue-makers. As they lay their eggs, or ‘nits’, females secrete a protein-rich liquid that quickly hardens into an exceptionally tough, water-resistant adhesive, cementing each egg firmly to the hair shaft. The same glue also helps to protect the developing embryo from drying out. Researchers are so impressed by its properties that they have suggested it could inspire new adhesives.
Lice have an equally inventive approach to reproduction. While most louse species reproduce sexually, a few favour parthenogenesis. Female cattle biting lice vastly outnumber males and can reproduce without them. Their unfertilised eggs develop into offspring that are genetic copies of their mothers – proper virgin births.
Perhaps their most ingenious trick comes when some bird lice need to abandon ship because their host has died. Small and wingless, these lice aren’t built for long-distance journeys. Instead, they hitch a ride on a passing fly, using it as an airborne taxi to get to another bird. This unusual form of transport is known as phoresis.
So perhaps Burns was a little harsh. Lice may be easy to dislike, but they are also astonishingly well adapted to their way of life. They’ve been making a living on the backs of other animals for millions of years – and, by the look of things, they’re not going anywhere soon.
top image: Head louse, computer illustration. Credit: SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY/ Getty Images
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