Review: Harbach, R.E. 2024. The Composition and Nature of the Culicidae (Mosquitoes). Centre for Agriculture and Bioscience International and the Royal Entomological Society, United Kingdom. ISBN 9781800627994

Despite the importance of mosquitoes (Diptera: Culicidae) as the vectors of pathogens that infect and cause disease in humans and other vertebrates, and after the past >150 years of research attention, their diversity, classification, and the evolutionary relationships between mosquito taxa remain incompletely characterized. For anyone who has worked to fill these gaps in our understanding over the past decade or so, Ralph Harbach’s Mosquito Taxonomic Inventory website has been an essential and authoritative resource that either answers many of our questions directly or provides us with the roadmap to arrive at our answers. Speaking from my own experience, when an out-of-place mosquito was found in Florida, a new country record, my first stop in identifying the specimen after recognizing it was not a native species was the Mosquito Taxonomic Inventory. Likewise, in Zambia, when I collected a puzzling mosquito from my colleague’s forehead that, at first glance, superficially resembled Toxorhynchites in coloration and length of the palps and overall size, but otherwise had the characteristics of Aedes, the Mosquito Taxonomic Inventory was our starting point on the path to identifying it as Aedes fulgens (Edwards) (Figure 1), a species of the subgenus Zavortinkius. The gestalt of this mosquito, to the eyes of someone most experienced with the mosquito fauna of the Americas, was unlike any Aedes I had previously encountered and after some initial excitement and confusion about its identity, the Mosquito Taxonomic Inventory quickly got us on track toward its identification. In every instance when I have been traveling and found mosquitoes of species, subgenera, genera, and tribes I had not previously encountered, I have turned to the Mosquito Taxonomic Inventory to provide me with summarized information on these new (to me) mosquito taxa and their morphological characteristics, and to guide me to the primary resources relevant to each taxon so I can identify and learn more about them. That website has been indispensable for me, and I expect for most everyone involved in the study of the diversity of mosquitoes, serving as a metaphoric GPS to mosquito taxonomy, classification, and morphology.

Figure 1:

Aedes (Zavortinkius) fulgens (Edwards) from the Choma District of the Southern Province, Zambia, identified with the help of the Mosquito Taxonomic Inventory, the precursor of The Composition and Nature of the Culicidae (Mosquitoes).

The Composition and Nature of the Culicidae (Mosquitoes) by Ralph Harbach is the evolution and immortalization of the Mosquito Taxonomic Inventory, which has recently faced an uncertain future. This book is a technical reference for mosquito classification and morphology that preserves the tremendous wealth of information compiled by Harbach over his career and that is, for now, available online. Although the Mosquito Taxonomic Inventory evolved over time, kept current by Harbach’s continual updates as species were described, as new mosquito fossils were discovered, as we learned more about relationships between taxa, and as relevant work was published, websites are impermanent. In 2024, the Mosquito Taxonomic Inventory went offline, much to the dismay of those around the world who rely on the information it contains. The Composition and Nature of the Culicidae (Mosquitoes) fossilizes the Mosquito Taxonomic Inventory into a resource that can always be available, regardless of what happens on or to the internet. It takes the utility of the Mosquito Taxonomic Inventory and reformats it into a >500-page book that will serve as a guiding reference to today’s and future mosquito taxonomists, researchers, and even mosquito control professionals, especially those involved in surveillance during this time of changing climates and changing species distribution.

While the number of professionals who are strict mosquito taxonomists, especially those focused on morphology, has dwindled with time, everyone involved in the study, surveillance, and control of mosquitoes needs taxonomic or morphological information on mosquitoes at some point. Understanding the classification of the organisms we study and their relationships to like organisms is and always will be essential to our work. Students, researchers, and academics working on the classification of mosquitoes are the group that I expect will be most benefitted by this book, but, as Harbach writes in the Preface, “Access to almost all other resources of mosquito information depends on scientific names and taxonomic infrastructure.” This book belongs on the desk or shelf of anyone engaged in work with mosquitoes, especially if they are identifying mosquitoes or studying their diversity, ecology, or evolutionary relationships. The utility of this reference will certainly vary by user, but much of the information that it contains is available together nowhere else (except the Mosquito Taxonomic Inventory, if it persists) or at least is not summarize and compiled anywhere else, making it helpful to have nearby and accessible. In my case, I am not a trained taxonomist, but I am intensely interested in the diversity of mosquitoes, and ever since this book arrived, it has sat, open, next to me on my desk, with multiple bookmarks in pages on various taxa for which I have specimens I am trying to make sense of, pages getting folded over as I rest my elbow on it while staring at the computer. The three most important utilities of this book, for me, have been the ability to flip to a taxon and conveniently find all the primary resources relevant to that group and their identification listed, the summaries of all that is known about each taxon (of which the bionomics subsections of taxa unfamiliar to me I occasionally peruse to reset my brain while between tasks during the workday), and the illustrated anatomical terminology section. The latter serves as an excellent reference, especially when interpreting old species descriptions or deciphering the characters described in older keys.

The Composition and Nature of the Culicidae (Mosquitoes) is subdivided into three sections: mosquito anatomy, classification and systematics, and anatomical terminology. The bulk of the book’s 500+ pages consists of the classification and systematics section (which addresses both extant and extinct groups). In this section, each taxonomic grouping of mosquitoes, from the family to the subgenus has a subheading, and beneath each, Harbach describes the taxonomic history of the taxon (with greater detail provided in Part V of the section) and summarizes the current state of understanding of its systematics, morphological characteristics, and bionomics – essentially everything that is known about each mosquito taxon above the level of species. Importantly, for each, he lists the principal references with some annotation, making it easy for the user to identify all relevant literature on a taxon of interest. The subsections on the morphological characteristics of each mosquito group includes the combination of characters that distinguish the species of a particular group from others. These subsections provide such characters for the adult, the male and female genitalia, the pupa, and the larva of each taxon, and are particularly useful in cases where a user is trying to determine the identity of a mosquito specimen of a species they have not previously encountered. The two sections that cover the anatomy of mosquitoes are thorough and cover all life stages. The figures are exceptional, and illustrate mosquito anatomy in fine detail with figures dedicated to, among others, the locations of scale patches on the mosquito pleuron and scutum, the wings, the male and female genitalia, the eggs, the mouthparts of the larva, and the spiracular apparatus of larva. This section will be useful to anyone involved in mosquito identification, including those in operational mosquito control and surveillance, as a quick reference for use alongside any keys to the morphological identification of mosquitoes.

The Composition and Nature of the Culicidae (Mosquitoes) primarily deals with mosquito taxa above the level of species. Between this and the other great compendium of information on mosquito systematics Mosquitoes of the World by Richard Wilkerson, Yvonne-Marie Linton, and Daniel Strickman, of which Volume 2 is a catalog of all described mosquito species (as of 2021), today’s mosquito taxonomist, researcher, or mosquito control professional has the past 260 years of study on the diversity of mosquitoes at their fingertips. Harbach’s book enables us to quickly answer questions about mosquito taxa above the species level, while the latter provides essential information (e.g., principal references, author, type locality, etc.) for each mosquito species (Mosquitoes of the World contains much more information, but this is what I have found most useful in my work). Although there is some overlap, these resources complement each other, and together, they provide or direct to a tremendous amount of information – essentially all that is known about each mosquito subfamily, tribe, genus, subgenus, and species. The Composition and Nature of the Culicidae (Mosquitoes) does include a list of all valid mosquito species, organized alphabetically by species epithet, but the real utility of this book (at least in my case) is above the level of species.

Whether you are describing a mosquito species, trying to make sense of evolutionary relationships among mosquito taxa, or just trying to determine the identity of a mosquito specimen of a species you have never encountered, The Composition and Nature of the Culicidae (Mosquitoes) is an essential reference. There are fewer mosquito taxonomists today than there have been since the link between Aedes aegypti (L.) and yellow fever virus was recognized. Given that we are living through a time when the natural world is undergoing rapid change driven by widespread landscape and land-use modification and global changes in climate, with mosquito species responding through changes in their distribution and diversity, it is essential that taxonomic knowledge of mosquitoes carries into the future and continues to grow to help us make sense of and respond to whatever mosquito-related issues the future holds. The Composition and Nature of the Culicidae (Mosquitoes) will help to facilitate this carryover, and to support the students and researchers who study relationships among the mosquitoes and who rely on the mosquito taxonomic infrastructure. Although many of us work on mosquitoes to better address their impacts on our species, mosquitoes are the most interesting group of insects on Earth and worthy of study in their own right. The Composition and Nature of the Culicidae (Mosquitoes) will be an essential reference as we work to better understand mosquito diversity both for the sake of mitigating their impacts, and for the joy of exploration and discovery among these fascinating and (still) poorly known insects.