WHAT goes on the list of the most abundant living things on Earth? Parasites should surely make the cut. They live within us and many other animals, as well as in plants and fungi, and slip under the radar while infiltrating almost every food web and ecosystem. They are mind-bogglingly diverse, with hardy and sometimes extraordinary ways of living and reproducing in their hosts.
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Parasites by Scott L. Gardner, Judy Diamond and Gabor Racz, all at the University of Nebraska State Museum, Lincoln, explores the world of parasitism and the ingenious tactics that have made it, according to the authors, the “most successful lifestyle on Earth”.
Such a feat is largely due to the ability of parasites to hop between hosts and exploit events such as species migration. From mussels in fish gills and 30-metre-long tapeworms in blue whales to the leeches that live in the anuses of hippos, parasites will sometimes pop up in places that even trained parasitologists least expect them.
This fascinating book touches on various types of parasite to illustrate how they are entrenched. It includes three key players, all worms: nematodes, flatworms and the behaviour-manipulating thorny-headed worms, which can make host insects and crustaceans bend to their will to increase the chances that they will be passed on.
It isn’t just animals that are parasites: the evolution of parasitic plants and fungi is “evidence that parasitism arises repeatedly as a sustainable lifestyle”, say the authors. In fact, parasites have been pulling the strings throughout human history. For example, the first widespread public health campaign in the US was aimed at eradicating hookworm infections in the early 20th century.
If you are having a hard time visualising such critters, the book comes with photos of some suitably unpalatable parasites, along with the animals and landscapes in which they are found.
But despite the great success of parasitism, the authors explain that parasites are still understudied – and some of them are even under threat. As they point out, “our knowledge of the Earth’s biodiversity catalog is still so incomplete that many species will vanish without ever having been identified. This is particularly true of parasites, since only a small fraction of them have been described.”
Time is short before climate change “burns the library” of biodiversity for good. The authors are calling for the same enthusiasm to be adopted in citizen science for parasites as it is with documenting other organisms, like birds, in order to untangle their mysteries and better understand how to control the diseases some of them cause, as well as to enrich our knowledge.
With its detailed accounts of these intriguing organisms, their modes of infection and transmission, and the scientific studies that have been undertaken to understand them – including some by Gardner himself – the book makes a case that parasites aren’t always “the bad kids on the block”.
This message might have been more impactful had the authors given more space to the mind-bending capacities of parasites, and to parasites other than worms, rather than focusing on their most everyday trick: infecting hosts.
After several repetitions of what is a very similar infection process, albeit with different parasites, the book ends up feeling a bit formulaic and you may wonder whether the writers are doing justice to the full flamboyance of their subject.
Even so, it is hard to overstate these organisms’ often-invisible power and influence over the world and so many of its inhabitants. One thing is certain: you won’t look at parasites in the same way again.
Gege Li is a writer based in London
