The Sad Story of a Rare Cat and Its Loyal Parasite

We had scarcely discovered the parasite Felicola isidoroi when it vanished forever.

Esther Aarts

The lynx, in our eyes, is a wildcat of unthreatening dimensions. It has tufted ears and a spotted coat. The ruff beneath its chin grows in two bunches, recalling the beards of the men of Byzantium. Its stubby, black-tipped tail makes you think it might have lost a more splendid appendage to a fire. The lynx is mostly solitary, and rarely seen. Its dens are found in forests and between boulders, in Europe, Asia, and North America. The bobcat, a species of lynx, lives in the Catskill Mountains—do you hear cat-skill or cats-kill?—hunting little mammals. Another species, the Iberian lynx, was once the rarest cat on Earth: For a time, there were just 94. Today, more than 500 Iberian lynxes live in Portugal and Spain; bringing them back cost more than $76 million.

The lynx, to a louse, is—but doesn’t this sound like the start of a Jorge Luis Borges story? To a louse a lynx is a meal of preposterous magnitude. Also, habitat. Unlike, say, fleas—ready defectors—lice are loyal. Each species tends to colonize a specific type of animal. And almost every furred creature is populated by a unique kind of louse. Though bobcat lice are strangers to the lice that roam lynxes in Romania, they have some similarities: They have dozens of young but care for none; they emit no noise. Some lice suck, and these tend to be homebodies (they live at the base of a hair). The Iberian lynx’s louse, by contrast, likes to chew. It wanders the lynx, stopping to lever up flakes of skin and create tiny blood lagoons from which to drink. It is intrepid, a description further justified by the fact that it is eyeless. The louse has no idea what its lynx looks like, and the lynx cannot see the louse either—though the lynx feels the louse acutely.

We had scarcely discovered the Iberian lynx’s louse before it vanished. The creature was identified in 1997 when an adult louse and a nymph (a baby louse) were removed from the pelt of a dead lynx; it was later named Felicola isidoroi. At the time, Iberian lynxes were in severe decline as a result of a virus in rabbits, their prey. With this decline, the domain of the isidoroi louse dwindled and its habitat fragmented, as lynxes were less likely to cross paths with one another.

When conservationists took Iberian lynxes into captive breeding programs, they deloused them, dewilding the natural environment that is a lynx. Even if the lynxes hadn’t been deloused, their lice may not have survived captivity. Wildcats in enclosures tend to overgroom and pace. These can be fatal events for a louse that’s scratched off or dislodged by fretful movement.

A given lynx likely does not mourn his lice (they itched him!), so why should we care about the lynx’s louse? As it turns out, we have good reason to pay heed to vanishing lice. Some biologists argue that parasites and their hosts should be viewed as one entity, because their interaction drives the evolution and health of both species. Their relationship may even render whole ecosystems more resilient. Perhaps, then, if we can’t save all endangered species, we should focus on saving those animals that host unique and rare clingers-on, both on the skin and within. Several parasites have been shown to aid immunity. The intestinal worms inside some fish sop up noxious heavy metals from the tissue of their carriers. A few parasites have been called “ecological puppeteers” for the ways they change the behavior of their hosts and alter the ecosystem—for example, prompting crickets to jump into streams, where insect-eating fish eventually flourish; or making moose more feeble, therefore supporting wolf packs.

Parasites can also teach us about their hosts. Because lice evolve alongside their hosts, the genome of a species-specific louse is an index card showing the history of its carrier species: former abundances of the larger animal, its adaptations and demographics. With the loss of the isidoroi louse, science lost a means of exploring the lynx’s past.

Another lesson we can learn from the lynx and its louse is that a host need not become extinct for the creatures that subtend it to disappear. We’re certain to have shared the world with other things that have died out, unmet and un-observed, altering entire ecosystems in the process. Every organism exists in relation to other organisms, and even the tiny, the irksome and squirming, warrant attention.

This article appears in the March 2019 print edition with the headline “A Parasitic Relationship.”