No historian of science will be surprised to hear that the humble leech has played an important role in the lives of humankind for centuries. Yet this new book in Reaktion's intriguing Animal series teases out far more than the long-running use of leeches for medical therapy, something which turns out to be just one aspect of the complex and ambiguous relationship that humans have held with these bloodsucking creatures over the years.

An exploration of the very word ‘leech’ reveals many of these complexities. Related both to the Anglo-Saxon word for ‘healer’ (physicians were also known as leeches) as well as the Middle Dutch for ‘worm’, in modern parlance the term ‘leech’ tends to denote a parasite. When we describe our fellow humans as ‘leeches’, it is generally this sense that we suggest: someone who sucks the life out of another or out of a social group without giving anything in return.

Yet, as Kirk and Pemberton rightly recognize, the animal itself cannot be dismissed so simply. This book thus shies away from the facile association of leeches with parasites to view them, instead, in a symbiotic relationship with humankind, whereby both man and leech have benefited from the creature's extraordinary abilities. This short but rich volume thus explores the leech as both animal and symbol, from ancient medical remedy to modern horror film, from emblem of capitalism to biomedical tool.

Much of the text, of course, does focus on the medicinal leech – Hirudo medicinalis. References to the use of leeches in healing have been found in ancient Arabic, Persian, Chinese and Sanskrit literature, as well as Greek and Roman culture. Leeching was particularly associated with humoral medicine, from antiquity to the early nineteenth century. In this model, disease was characterized as an imbalance of bodily fluids: blood, black bile, yellow bile and phlegm. The leech's ability not only to remove blood, but also to promote continued blood flow from a bite wound, due to the anticoagulants injected, was highly valued in bloodletting.

Yet bloodletting is not the only way in which humanity has utilized leeches: one of the more surprising methods revealed here is the use of leeches to predict the weather, best represented by George Merryweather's impressively ornate invention, the ‘Tempest Prognosticator’. In more recent times, leeches in the laboratory have assisted with experiments on the functioning of the muscles and nervous system and on nerve regeneration. In surgery, leeches continue to be used for reconstructive and cosmetic operations, particularly those involving microsurgery, and leech-produced hirudin remains superior to many pharmaceutical derivatives. As the authors remind us, ‘human inventiveness cannot as yet rival the sanguivorous experience of the leech’ (p. 114).

For those who see the bloodsucking worm as the stuff of nightmares, there may be some areas in which repeated attempts to emphasize an intimate relationship between human and leech seems a little over the top. Indeed, the authors exhibit a tendency throughout to anthropomorphize the creature, suggesting, for instance, that leeches ‘care and provide for their young as any human parent might’ (p. 28). Yet this very approach complements the overall argument of the text, encouraging us not to view the leech as ‘other’: an approach supported by the many historical examples drawing comparisons between man and leech. Lord Chancellor Thomas Erskine, we are told, was so taken with the two leeches he believed had saved his life at the turn of the nineteenth century that he kept and named the creatures, crediting them with his own emotions, for ‘he was sure they both knew him, and were grateful to him’ (p. 72).

This reminds us that it is our preconceptions that may lead us to regard leeches as hideous. Anyone who has ever watched the characteristic, wave-like swim of the creatures will certainly agree with the description of their movements as possessing an ‘elegance few other creatures can rival’ (p. 25). It is not, Kirk and Pemberton note, necessary even to view blood-feeding as negatively parasitic: many leeches, such as those generally used in medicine, have adapted to draw quantities of blood that are not damaging to their hosts. Indeed, reflection on the human–leech relationship can even be used to challenge other assumptions we hold as to what is positive, useful or normal. The sexual life of leeches is one of many such examples. Although hermaphrodites, leeches are protandric: that is, their male genitalia mature first, with the female organs following later in life. Leech sexuality is thus not fixed, but alters with time, something which the authors suggest may challenge the male–female binary on which so much of human identity rests. The differences between leech and human, then, may offer us as much insight as the comparisons.

Well illustrated and engagingly written, this book draws together huge numbers of historical and cultural depictions of leeches, moving seamlessly from Dr Broussais (the early nineteenth-century ‘vampire of medicine’) to the twenty-first-century science fiction of the X-Men. These effectively illustrate the central message: a reconsideration of our relationship with the leech, as well as an effort to challenge the way the assumptions held about the creature have been used to underpin human identity. Written for a popular audience, there is nonetheless much to recommend this work to specialists: the authors ably tie their historical and cultural research to the natural history of the leech, offering an interesting perspective on the history of science. As the authors conclude, recognizing the historical and cultural manner in which human–leech relationships have been created offers us a means of changing them.