Entomology
Entomology
Entomology is the branch of zoology dealing with insects. It includes the study of the development, anatomy (structure), physiology (functions), behavior, classification, genetics, and ecology of insects. It is a fascinating branch of science because by their sheer numbers, insects are considered to be the dominant group of animals on Earth today.
Based on the Greek word entomon for insects, entomology is the scientific study of insects. As with most branches of zoology, entomology was first seriously studied in the work of the Greek philosopher Aristotle (384–322 b.c.). It was he who gave the first good descriptions of insect anatomy and laid the groundwork for entomology by stating that all insects have a body divided into three parts. After Aristotle's work, there was little attention paid to insects except to add more types to the list of known species. However, in 1602, the Italian naturalist Ulisse Aldrovandi (1522–1605) devoted an entire book to insects called Of Insect Animals, and by the time the microscope was invented in the latter part of that century, two men in different countries made the first accurate studies of insect anatomy. In Italy, the physiologist Marcello Malpighi (1628–1694) turned his microscope on insects and discovered the tiny, branching tubes with which they breathe. He also devoted an entire volume to the interior organs of the silkworm. About the same time in Holland, the Dutch naturalist Jan Swammerdam (1637–1680) was doing such excellent and highly detailed studies on insect anatomy, that he came to be considered the founder of modern entomology.
JAN SWAMMERDAM
Dutch naturalist Jan Swammerdam (1637–1680) is considered to be the founder of entomology or the study of insects. He also was the first to observe red blood corpuscles (an unattached body cell) and did a great deal of work in comparative anatomy (the study of the structure of living things).
Swammerdam's life always seemed to be characterized by extremes. Although he led a productive life, it also was extremely difficult and sad. Born in Amsterdam in the Netherlands, the son of an apothecary, or pharmacist, Swammerdam was interested in natural history and particularly insects at a very early age. Although his father sent him to medical school, he intended that his son become a priest. When the young Swammerdam graduated from the University of Leiden, he took up the study of natural history and never practiced medicine. Since he had also refused to become a priest, his father decided not to support him and cut him off from any financial help. Despite a lack of money, Swammerdam continued to pursue his biological studies and did an enormous amount of work under very difficult conditions.
Swammerdam studied the life cycles and anatomy of many species of insects, particularly honeybees, mayflies, and dragonflies. Using his microscope, he made several discoveries about what goes on when certain insects undergo complete metamorphosis. This is when it experiences a complete change in its body shape, such as when a caterpillar turns into a butterfly. From these observations of metamorphic development, Swammerdam was able to classify insects into four major groups, three of which are accepted and used today in insect classification. Aside from this, one of his most significant achievements may have been simply to disprove some of the false notions about insects.
Until Swammerdam demonstrated that insect bodies have real structure and internal organs, most had considered them to have simply fluid-filled cavities with no specialized organs. Since virtually every habitat on land contains insects, and they make up about three-quarters of all the animal species on Earth, Swammerdam was finally giving nature's most prolific and most successful class of animals their due. For example, his detailed drawings and descriptions of their reproductive organs showed that they reproduced sexually rather than via such ancient myths as spontaneous generation (which said that living things can be generated from nonliving things).
Swammerdam also used his microscope to study some of the internal systems of vertebrates (animals with a backbone). In 1658, he documented certain small particles that he observed in the blood of a frog, making this the first time that anyone had ever seen red blood cells. He discovered valves in the lymph system (a network of vessels that carry lymph throughout the body) of mammals and also studied the fertilization of eggs as well as their development into an embryo. Experimentally, he showed that the muscle removed from a frog's leg can be stimulated and made to contract. He also theorized and made an excellent guess about the role of oxygen in respiration. He even pioneered the practice of injecting dyes into a cadaver (a dead body) in order to better observe certain anatomical details. Unfortunately, Swammerdam never published his work and most of it went unknown during his lifetime. Since he had little or no income, he did without a great deal and actually suffered both physically and mentally. Eventually he became sick and undernourished, and with overwork and worry, he soon became depressed and mentally unstable. In 1673 he came under the influence of a cultlike figure to whom he remained devoted until his death at the age of forty-three. It was not until 1737 that the Dutch physician Hermann Boerhaave (1668-1738), discovered Swammerdam's work and paid to have it published. Titled the Bible of Nature, this two-volume Latin translation of his Dutch work contains some of the finest illustrations of insects ever produced and served to lay the foundation for entomology.
Today's entomology deals with a group of animals that are by far the largest of all the classes. There are more than 800,000 known species of insects, and it is estimated that there may be an equal number of still-unknown species. Insects belong to the phylum Arthropoda, which is considered the most successful group of animals on Earth. This is because insects have lived on Earth for about 350,000,000 years, while humans have been on Earth less than 2,000,000 years. While insects are considered pests by many people, they are in fact highly beneficial to humans in a number of ways. Insects perform many important functions in any given ecosystem (an area in which living things interact with each other and the environment). Many insects are soil-dwellers, wood-borers, and consumers of dead animals, and therefore help in the decomposition process (breaking things down) and in the recycling of nutrients. Many insects are eaten by fish and birds and are thus an important food source. Many insects kill and eat other insects, helping to regulate populations. Many flowering plants are dependent on the pollinating activities of bees, butterflies, and flies in order to reproduce. Insects also provide people with a number of useful products such as silk, wax, and honey. On the other hand, insects can be terribly harmful by causing huge losses of food and acting as transmitters of diseases to humans, plants, and animals.
Modern entomology has two aspects: the scientific side that simply wants to learn as much as possible about all insects, and the practical or applied side (often called economic entomology) that searches for methods to better control insects. This latter part of entomology investigates the physiology, development, genetics, diseases, and behavior of pest insects in order to discover new ways of controlling insect populations. For example, research on insect development has led to the use of specific chemicals that disrupt certain hormones important during metamorphosis (as when a caterpillar changes into a flying insect). Other investigations have shown ways to use chemicals to modify insects' behavior (and perhaps confuse them during their mating cycle). Such methods, when combined with traditional chemical pesticides, come under the term pest management. However, entomologists do not want to exterminate all insects. Rather, they hope to control and limit any bad effects insects may have. This is probably wise, since most people who study insects realize there are many good reasons why insects are beneficial to humans, and why insects are the most abundant and most successful animal group ever.
Insects can also be enormously interesting. They have a skeleton on the outside of their bodies; they have no lungs; they smell with their antennae; and some taste with their feet. Some hear with special organs in their abdomens or front legs. Some are highly social and live in colonies. Because insects are highly adaptable, many people say that only insects will remain after every other living thing has disappeared from Earth.
[See alsoInsects ]
Entomology
Entomology
Entomology is the study of insects. It is a major branch of animal zoology. Insects are one of the most successful and diverse groups of living organisms in the world today. Approximately 1.5 million species of insects have been identified by scientists as of the end of the twentieth century. However, it is estimated there may be as many as twice that number on Earth. The number of insect species is greater than the number of all other species of organisms combined. It is estimated that there are about 200 million insects for every living human. Insects are members of the kingdom Animalia, the phylum Arthropoda, and the class Insecta. Insects share the major group Arthropoda with creatures such as crabs, lobsters, shrimp, spiders, scorpions, ticks, mites, centipedes, and millipedes. Common insects include ants, butterflies, bees, cockroaches, beetles, flies, grasshoppers, mosquitoes, dragonflies, moths, wasps, and termites.
Insects have a tough exoskeleton (external skeleton) and three pairs of walking legs. The majority of insects have wings, and those with wings have two pairs, except flies, which have only one pair. Their bodies are divided into three regions: the head, thorax, and abdomen. All insects hatch from an egg in a form which is different from that of the adult insect. A well-known example of this is the caterpillar (the larval stage) and butterfly (the adult stage). Insects are characterized by their small sizes and short lifespans.
Scientists believe that insects have inhabited Earth for about 380 million years. They occupy nearly every type of environment except for salt water. They are most numerous in tropical climates and on land. Their enormous success is believed to be due to three main factors: their exoskeleton, size, and diet. Their tough exoskeleton protects them against physical damage and water loss. Their small size allows them to occupy many small areas unavailable to larger animals. Small size also allows for a faster reproductive rate. Finally, insects eat almost anything and everything.
Insects play many important roles in nature. Insects such as bees, butterflies, moths, and flies pollinate flowering plants. Many insects aid in the decomposition process and nutrient cycling, or exchange. Insects are important food sources for other animals, such as birds, and also eat other insects, thus keeping insect populations in control.
Most entomologists work in the field of economic entomology, which is also called applied entomology. They study the small minority of insects that are harmful to humans. Harmful insects include those that destroy crops and buildings and those that transmit diseases to humans. Insects that feed on plants such as grasshoppers destroy plant crops and timber. Other insects transmit plant diseases. Insects such as termites destroy wood buildings. Bloodsucking insects such as mosquitoes, lice, and fleas transmit some of the most serious infectious diseases in the world. These include malaria, dengue fever, yellow fever, bubonic plague, and typhus.
Scientists attempt to reduce the number of insect pests through a variety of ways. Cultural controls include the draining of swamps where mosquitoes breed. Chemical controls include the use of pesticides and insect repellants. Biological controls include the use of animals that naturally prey on insect pests.
People are also inadvertently decreasing the number of insects by destroying their natural habitats. Destruction of natural areas by human activities is wiping out species of insects that we will never even know existed. What wondrous creatures are we missing?
Denise Prendergast
Bibliography
McGrath, Kimberley A. World of Biology. Farmington Hills, MI: The Gale Group, 1999.
Preston-Mafham, Rod and Ken Preston-Mafham. The Natural History of Insects. Ramsbury, Marlborough, Wiltshire, UK: The Crowood Press Ltd., 1996.
Entomology
Entomology
Entomology is the study of insects and their life cycles. Many insects live and feed on dead flesh, which is why entomology is relevant to forensic science . The forensic entomologist can help estimate time of death by looking at which insects are present on a corpse and where they are in their life cycle. Entomology can also shed light on the nature of injuries, whether a corpse has been moved, and whether drugs were involved in a death.
A newly deceased corpse attracts flies. Within minutes of a death, blowflies will start to lay their eggs in moist areas such as the nose, mouth, armpit, groin, or open wounds. The eggs hatch into larvae or maggots within 24 hours and these grow to around half an inch in length after about three days. Then, over the next six to ten days, they will develop into pupae with a hard outer case. Adult flies emerge about twelve days after this. If the corpse is not recovered by this time, the life cycle repeats itself so that flies at all different stages of development may be recovered from the corpse.
The forensic entomologist can use the life cycle of the flies found on a corpse as a kind of clock, giving the minimum time that elapsed since the time of death and the time of discovery. If eggs are found, it suggests death occurred less than 24 hours before discovery. The presence of maggots indicates the death occurred less than ten days ago. Pupae and mature flies will suggest a time of death one to three weeks before discovery of the corpse. However, the life cycle of flies is not an accurate clock. Flies are cold-blooded and their activities are dictated by the weather. Maggots may become dormant if it is cold and flies do not lay eggs at night. If someone is killed at midnight, flies will not appear till daylight, which means time must be added to the estimated time of death.
Because flies feed on human tissue, their own tissue can sometimes be used to measure levels of any drugs that may have played a role in the person's death. This is useful when the corpse itself does not yield tissue for analysis. Insect ecology varies from place to place and sometimes the species found on a corpse are not native to the place where the corpse is found. This may indicate that the corpse was moved after death. Furthermore, flies feed on open bleeding wounds and their presence may help distinguish between ante-mortem and post-mortem injuries.
see also Time of death.
entomology
en·to·mol·o·gy / ˌentəˈmäləjē/ • n. the branch of zoology concerned with the study of insects.DERIVATIVES: en·to·mo·log·i·cal / -məˈläjikəl/ adj.en·to·mol·o·gist / -jist/ n.