Insect Museum

Sonia Dourlot is a photographer with the Eco-biology of Parasitoid Insects unit at the University of Rennes, France. She studies the biology of those insects that may be able to assist humans biologically fight insects that are pests.

Introduction

We have a common, natural tendency to consider spiders, millipedes and woodlice as insects. None of them belong to this group: each of these animals belongs to distinct classes of the animal kingdom. The ensemble of these invertebrates belong, on the other hand, to the same phylum, that of the arthropods. This book does not only outline insects but also other arthropods.

BIODIVERSITY

Arthropods are by far the most abundant animals on our planet. To underscore their significance, suffice it to say that of the nearly 1.5 million species of plants and animals described up till now in our world, about 1.2 million are arthropods, among which there are 950,000 species of insects! It is difficult to provide exact figures, since with the passage of each year, new species are discovered. Therefore, more than 5,000 insect species are described each year. To estimate the number of species currently in existence is thus a very tricky exercise. The numbers given encompass a broad range from 6 million to 50 million.

Arthropods: What are they and how many are there?
We give the name arthropods (arthro = articulation and pod = foot) to all invertebrates with an external skeleton (exoskeleton) and with articulated appendages.

SYSTEMATICS

The birth of systematics
In order to organize the vast knowledge about species, it became necessary to give each a name to unambiguously identify and classify them. The Swedish botanist Carolus Linnaeus (1707-1778) thought, and rightly so, that ignoring the name of things contributed to having less knowledge about them. Thanks to his ordered way of thinking, he organized, mostly on the basis of anatomical criteria, the branches of natural history in his book Systema Naturae. He established the foundations of zoological nomenclature and, more significantly, introduced binomial nomenclature. Though plant species dominate his work, he also described some 3,000 insects. Johann Christian Fabricius (1745-1808) continued the work of the Father of Systematics, and went on to describe more than 1O,OOO insect species on his own.

Classifying...
Systematic hierarchy is based entirely on taxonomical rankings. Therefore, for the Seven-Spotted Ladybug, the classification is established as illustrated in the drawing to the left.

The impressive number of classification categories may appear overdone at first and pointless to a many of us. However it remains critical to fully describe, in a precise fashion, a ladybug from the considerable number of other like species in the living world.

Note that the suffixes (-oidae, -idae, -inae, etc.) of the taxonomic names inform us of the ranking of that name. It is rare to be able to identify a species with complete certainty. For the most part, you must use a word that refers to the family, with an identifying key, to arrive with any degree of certainty to naming a specimen. Investigation is often undertaken with a microscope, scrupulously noting all identifying characteristics. The first time around, progress among the different species is slow and fastidious. For certain groups, identification is only possible by comparing the external genitalia of related species.

...and naming
When a new species is discovered, its discoverer will give it a scientific name and register it with the International Commission on Zoological Nomenclature. The scientific name, established along the principles of binomial nomenclature, is composed of the genus name (most often of Greek origin) followed by the name of the species (in Latin). This name is then followed by the name of the discoverer and the year of the description.

For example, let us consider the cetonian known as the Rose Chafer. This species was described by Linnaeus in 1761 under the name Scarabaeus auratus Linnaeus, 1761. But in 1775, Fabricius distinguished the cetonians from other scarabs and assigned a new name to the genus: Cetonia. The species' name remained the same, though it was conjugated to agree with the feminine name preceding it, to become aurata. To note such a modification, it was agreed to place the name of the discoverer and the date of his discovery in parentheses. Consequently, the scientific name of the Rose Chafer will from now on be Cetonia aurata (Linnaeus, 1761).

During Linnaeus' time, Latin was the common scientific language. Today, we continue to use both Latin and Greek for scientific names. This nomenclature offers the quality of universality: the scientific name allows one to designate, without ambiguity, the same species in all countries of the world.

...and phylogeny
The traditional mode of classification, used since Linnaeus' time, was established along almost exclusively morphological criteria. By a fortuitously good choice we have since established a classification system that also provides a fairly accurate picture of the parental links between living species. In fact, the morphology of a species is determined by its genes. Therefore, a bee more closely resembles a wasp than it does a cow since the last common ancestor shared between bees and wasps is much less distant in the past than the last common ancestor (there surely was one!) of bees and cows.

However, occasionally these similarities might be misleading or even erroneous, since certain organisms may look alike without necessarily having a close common ancestor. The important progress made in the field of genetics (one can now "read" the DNA sequences of most living organisms) has provided the means to correct certain errors made when taking a solely morphological approach to classification. For example, it has been shown that crocodiles are in reality closer genetically to birds than to lizards though, at first glance, a crocodile would be thought to resemble an iguana much more than a robin! Modern classification, which is uniquely founded on parental links brought on through evolution (a classification system called phylogenetic) continues to evolve from day to day, in light of the latest discoveries. Therefore, contrary to general opinion, classification is very much a vital, living, dynamic science, which utilizes the most modern technological tools to study the living world. It is, however, a science that still respects its origins, acknowledging that its foundation is based on data methodically gathered over three centuries.