Flea systematics is currently based entirely on morphology. The anatomy of fleas follows the basic gross morphological pattern of the Class Insecta, however, because of their parasitic mode of life on mammalian and avian hosts, they have evolved extreme adaptive modifications. Many of these morphological features are exclusive to Siphonaptera. They have developed ctenidia (combs) on their heads, thorax, and abdomen and occasionally on their legs. Setae occur in every size and shape and in a multitude of numbers and positions. The aedeagus of the male is likely the most diverse and complicated of any arthropod in existence. They have evolved a variety of parasitic life modes. Some are nest fleas (Anomiopsyllus, Jordanopsylla, etc.), some spend much of their time crawling through the pelage of their host (Orchopeas, Xenopsylla, etc.), some have adapted to a sessile, or “sticktight” mode (Echidnophaga, Hectopsylla, etc.), some are somewhat free living in the environment and intermittently feed on their hosts as opportunists (Pulex, Vermipsylla, etc.), while yet others attach and become endoparasitic (Tunga and Neotunga). Although these examples are represented by only a few genera, most fleas fall within one of these descriptive categories. The exceptions to any rules of development are ever present among fleas. Flea taxa from various continents may manifest convergent or divergent patterns of evolution from sister taxa remotely located. Their micro-environmental requirements and host diversity are as varied as the number of species.
Flea systematists recognized very early that member of the Order Siphonaptera were morphologically extreme and diverse. To describe the anatomical structures (with correct homologies of related arthropods) was an evolution in itself! Thanks to the great dedication and contributions of early “pulicologists”, (Karl Jordan, Nathan C. Rothschild, A. C. Oudemans, Julius Wagner, Frans Peus, Andersen Hubbard, George Holland, Robert Traub, G.H.E. Hopkins, F.G.A.M. Smit, and Miriam Rothschild), the terminologies germaine to describe most of the structures were developed and scattered throughout the literature. These were gathered into a brilliant and comprehensive compilation of generally accepted terms resulting in the 1971 publication entitled, “A Revised Glossary of Terms Used in the Taxonomy and Morphology of Fleas” by Miriam Rothschild and Robert Traub. This text is reprinted as a separate “manual” from its parent volume, “An Illustrated Catalogue of the Rothschild Collection of Fleas (Siphonaptera) in the British Museum (Natural History)”, Volume V, pp. 8-85, G.H.E. Hopkins and Miriam Rothschild, Trustees of the British Museum (Natural History), London: 1971. The complexities of the aedeagus are beautifully illustrated from a three dimensional point of reference in the “Glossary”. Additional morphological terms may also be found in other companion volumes to the the works of Hopkins and Rothschild.
The existing trend of not replacing aging and dying systematists throughout the world (among most entomology disciplines) necessitates endeavors to foster new and “budding” systematists. We are grateful to The Honorable Miriam Rothschild and to the Trustees of the British Museum (Natural History) for granting us permission to reproduce selected figures from “A Revised Glossary…of Fleas” as computerized images. It is our purpose to present the major elements of basic flea morphology as presented in the “Glossary” to interested scientists (young and old alike). We hope by increasing the accessibility of this beautiful and most useful work that it will foster the interest of new promising flea systematists and promote the use of standard terminology by those currently engaged in systematic studies of fleas.