Entomology

Entomology (pronounced en-toe-MOLL-oh-gee) is a branch of zoology concerned with the study of insects and their effect on humans, other organisms, and the environment. Entomology has many applications in society beyond its value in identifying and classifying insects. For instance, studying the life cycles of insects can be used in the forensic study of crimes. Entomologists may also use their skills to trace and prevent the spread of insect-borne illnesses; develop biological and chemical pest controls; promote methods to protect food, timber, and livestock from damage by insects; and study biological diversity.

The word entomology is derived from the Greek words entomon (meaning "insect") and logia (meaning "study" or "knowledge"). Insects represent one of the oldest and largest categories of animals, and human understanding of their biology can have important and useful applications for a number of other fields, including genetics, ecology, chemistry, paleontology, and pathology. The first known insects appeared on the genealogical record more than four hundred million years ago, and scientists estimate that between three and thirty million insects may exist. Of the five to thirty million species of life believed to potentially exist on Earth, roughly one million have already been officially identified as insects, with twenty thousand new species recorded annually. The sheer number and variety of insect species are a testament to their successful ability to adapt to a multitude of environments.

Classification of Insects

Entomology is primarily concerned with the study of insects, a massive category of related invertebrate organisms. Invertebrates include any organism that lacks a spine. Approximately 97 percent of all described living animals are classified as invertebrates, and 75 percent of all invertebrates are insects. According to the taxonomic system of organizing all lifeforms into an organized zoological framework, every identified organism will be assigned to a kingdom, phylum, subphylum, class, order, family, genus, and species.

Insects are classified as belonging to the phylum Arthropoda, a category that is classified as part of the broader kingdom of Animalia. In addition to being invertebrates, arthropods have a segmented body and jointed appendages. Arthropods include crustaceans (such as crabs), arachnids (spiders), and myriapods (centipedes). Within this phylum, insects are categorized as part of the subphylum called Hexapoda, which includes insects and three other classes of wingless arthropods. The largest class within Hexapoda is known as Insecta, and it contains all species of animals zoologically categorized as insects. Insects are defined as invertebrates that have three pairs of jointed legs, a segmented body that is divided into three parts (a head, abdomen, and thorax), an exoskeleton, antennae, and a set of compound eyes. Insects have colonized virtually every environmental niche on the planet, from the oceans to mountain peaks.

Insects as a taxonomic class represent one of the oldest forms of life. Insects are thought to have first evolved during the Ordovician period more than four hundred million years ago. They evolved largely in coordination with the evolution of flowering plants. Although there is great uncertainty about the origins of insects, scientists speculate that insects evolved from the subphylum known as Myriapoda, which contains millipedes and centipedes. During their early history, insects lived alongside (and ultimately outlasted) both dinosaurs and their fellow arthropods known as trilobites. The oldest known insect fossil is that of Rhyniognatha hirsti, a type of small springtail with a large set of triangular jaws that may have also had wings. It is thought to have lived in Scotland between three hundred and four hundred million years ago. Although insects were well established as a class two hundred million years ago, they underwent several periods of mass extinction and great expansion—most recently sixty million years ago, when the dinosaurs went extinct. Many of the insect species from this period likely bore a strong resemblance to the insect species alive in the contemporary era.

Insects are divided between twenty-four and twenty-nine taxonomic orders, depending on the source. Some of the better known orders include Blattodea, cockroaches and termites; Coleoptera, beetles; Diptera, flies and mosquitos; Hemiptera, aphids, cicadas, and leafhoppers; Hymenoptera, ants, bees, and wasps; Lepidoptera, butterflies and moths; Mantodea, praying mantises; Odonata, damselflies and dragonflies; Orthoptera, crickets, grasshoppers, locusts, and katydids; Phasmatodea, stick insects; Phthiraptera, lice; and Siphonaptera, fleas. The largest numbers of species belong to the orders of Coleoptera, which includes more than four hundred thousand identified beetles and the Lepidoptera order of butterflies, which has more than one hundred thousand species. On the other hand, the Notoptera order of insects contains less than fifty known species of wingless bugs that live in extreme high-altitude environments, while the Zoraptera order of tiny termite-like insects contains fewer than forty known species.

Brief History

From the beginning of their shared history on Earth, insects have had a major influence on humans. Researchers have discovered evidence that prehistoric humans were infected with fleas, lice, and other parasites that likely spread disease and shortened life spans. Biblical passages, such as Exodus 8:16–24, describe locust swarms that destroyed crops. Some insects even evolved to use humans specifically as host subjects. For instance, lice are highly host specific, meaning that many species have adapted to live on a single species. Humans are host to three species: head lice, body lice, and crab lice. Body lice evolved from head lice in response to the growing human habit of wearing clothes.

Insects have had beneficial effects on human development as well. While roughly 1.5 percent of insects negatively affect humans, most have either no effect or instead serve positive roles for humankind. For example, insects pollinate 80 percent of the world's major crops. Insects are similarly responsible for decomposing waste, aerating soil for crops, and eating other insects that destroy human food sources. Insects are themselves a major food source in many cultures. They may also serve important roles in many ecosystems. In fact, insects' pollination of flowering plants helped provide the means for mammals to evolve in the wake of the dinosaurs' extinction.

The first specialized study of insects may date back to the Chinese domestication of silkworms approximately five thousand years ago. Humankind's scientific study of insects dates to the Greeks, when Aristotle used insects in his studies of deductive reasoning in the fourth century BCE. Although it was not called entomology at the time, scientists used entomological principles to examine insect metamorphosis or present methods to control insect populations to limit their negative impact on crops and human health. Insects changed the course of human history when fleas infected with the Yersinia pestis bacteria killed one-third of the European population during a fourteenth-century plague called the Black Death. However, it was not until the late nineteenth century that the role of fleas was identified in the spread of the plague, a discovery made in part due to the efforts of entomologists.

One of the major milestones that enabled entomology to develop as a science was the invention of the microscope in 1599. By the early seventeenth century, scientists such as Marcello Malpighi and Jan Swammerdam capitalized on this new technology to examine the anatomies and life cycles of insects. Entomology took another step forward when Francesco Redi determined that insects were born from eggs rather than arising from spontaneous generation as had been previously believed. Charles Darwin's theory of evolution and Carl Linnaeus's taxonomic system presented entomologists with new arenas in which to study entomological interests. Both scientists used the study of insects to help frame their broader scientific ideas. For instance, Darwin correctly postulated about the existence of a species of insect pollinator based solely on the shape of an orchid's reproductive organs, while Linnaeus used insect wings as a tool for classification.

By the nineteenth century, entomology had been firmly established as an independent field of zoological study in Europe. Texts such as William Kirby and William Spence's Introduction to Entomology helped create a firm foundation for the discipline. Advances like the discovery of DNA and the creation of vaccines have been used to make enormous progress in entomological pursuits in the twentieth century.

In the contemporary era, insects are regarded as valuable laboratory species due to their short life spans, easy care, and large numbers of offspring. In addition, as all organisms use the same genetic processes of replication and transcription, understanding how they work in small model organisms (such as some types of insects) can be used to further research higher lifeforms. For instance, the common fruit fly (Drosophila melanogaster) and the Anopheles gambiae mosquito were among the first organisms to have their genomes sequenced in 2000 and 2002, respectively.

In 2014, entomologists and other scientists were able to establish an evolutionary tree for the entire insect class. Using the 1,478 protein-coding genes found in all major insect orders, these researchers built a massive database that allowed them to estimate when all insect species may have likely evolved.

Careers in Entomology

A specialized degree in entomology requires both undergraduate and graduate credits. On an undergraduate level, entomology is offered as a degree at universities in every US state, and most universities have entomology classes available even when they do not have a dedicated entomology department. An entomology program may ask students to take classes in such specialties as biology, ecology, chemistry, pathology, and immunology. Professional entomologists who plan to pursue research studies will need a master's and possibly a doctorate degree in entomology. Many doctorate level entomologists take jobs in ecology, land management, conservation, agriculture, and biological research.

Approximately eight thousand professional entomologists are employed in the United States, and perhaps tens of thousands more pursue entomology as a hobby. While the US Bureau of Labor Statistics (BLS) does not provide salary information for entomologists, it places them in the category of zoologists and wildlife biology, which had an annual average salary of more than $70,000 in 2023. In the United States, many entomologists are enrolled in the Entomological Society of America (ESA), which was founded in 1889 and has a membership of six thousand professionals. It publishes six academic journals and the American Entomologist, a quarterly publication geared toward both professional and amateur entomologists.

Many types of careers exist in entomology. A research entomologist concentrates on studying particular aspects of insects, such as their anatomy, lifecycle, breeding, or behaviors. Governmental agencies, nonprofit organizations, private corporations, or universities may employ entomologists. Their work can be conducted in either laboratory or field settings. Many research entomologists also work in academic settings, where publishing research papers is a requirement of the profession. Many research entomologists often specialize in a particular type of insect. Researchers who focus on grasshoppers are called orthopterists, for example.

Forensic entomology is a relatively new field of research. While entomologists had long realized that the presence of insects could be used to date events such as crimes, it was not regarded as a legitimate means of criminal investigation until the late twentieth century. Since that time, forensic entomology has been increasingly used as a method of determining the time of death of victims, to identify the exact location of crimes, to explore health code violations, and to review issues with the contamination of commercially distributed food items. In the case of criminal investigations, the presence of different insects at various sites may show that a victim's body was moved. Similarly, certain insects, such as some kinds of flies, are prone to gathering around a recently deceased corpse. The presence or absence of maggots or other types of insects that are typically later arrivals can help determine the time of death. Entomotoxicology is a new subdiscipline of entomology in which insects found at a crime scene can be tested to determine whether drugs were present in the blood system of a victim.

Another important branch of entomology is concerned with medical research. Medical entomologists explore how pests like mosquitoes and fleas spread diseases, and then find methods to prevent or cure the resulting illnesses. Military agencies have increasingly approached medical entomologists to find ways to inoculate troops against insect-borne illnesses endemic to various military conflict zones. Veterinary entomology is a related field of medical entomology that seeks to prevent and control diseases in pets and agricultural livestock.

Agricultural entomologists often work for state or federal agencies to detect the presence of damaging insects and find ways to reduce their numbers or limit their damage. Some entomologists are employed at the federal level to help prevent the introduction or spread of invasive species of insects. Invasive insects are estimated to have cost North America more than $27 billion in crop losses in 2021 and $70 billion in losses annually on a global scale. The spongy moth, formerly called the gypsy moth, as accidentally introduced into the American Northeast in 1869. According to the US Forest Service in 2022, state and federal governments spent $282 million from 1980 to 2020 to treat outbreaks on 14 million acres. Agricultural entomologists may work with US Customs and Border Protection to prevent invasive insects from entering the country on food crops or other imported materials.

Scientists who conduct research to control populations of insects that damage agricultural crops or spread disease are involved in a speciality of entomology called integrated pest management (IPM). According to Statista, the US pest control industry was a $24 billion industry in 2023. Entomologists play key roles in the development of chemicals designed to affect only targeted insects without disturbing other parts of an ecosystem. They may also study natural methods of pest control that involve introducing predators that specifically target certain species of insects.

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