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Insect: the story on HearLore | HearLore
Insect
The word insect comes from a Latin root meaning cut, a description that has defined these creatures for over two millennia. Pliny the Elder introduced the term to the Latin world by calquing the Ancient Greek word entomon, which Aristotle used to describe life forms with notched bodies. This etymological root reveals a fundamental truth about the animal: their bodies are segmented into three distinct parts, a design that has allowed them to dominate the terrestrial landscape. The oldest fossil that may be a primitive wingless insect is Leverhulmia from the Early Devonian Windyfield chert, dating back to a time when the first forests were just beginning to take shape. These early ancestors were small, soft-bodied, and fragile, yet they possessed a chitinous exoskeleton that would become the defining armor of the class. The body is organized into three interconnected units: the head, thorax, and abdomen. The head supports a pair of sensory antennae, a pair of compound eyes, and three sets of modified appendages that form the mouthparts. The thorax carries the three pairs of legs and up to two pairs of wings, while the abdomen contains most of the digestive, respiratory, and reproductive structures. This three-part body plan is the key to their success, allowing for specialized functions in each segment that no other animal group has matched.
The Silent Architects
In the Carboniferous age, the atmosphere was thick with oxygen, allowing insects to grow to sizes that seem impossible today. The dragonfly-like Meganeura had a wingspan of up to 70 centimeters, a giant that ruled the skies of the Paleozoic Era. These ancient giants were possible because the respiratory system of insects, which relies on a network of tubes called tracheae, was able to deliver oxygen directly to tissues without the need for lungs. As atmospheric oxygen levels dropped, the size of insects was constrained, and the heaviest insect currently weighs less than 100 grams. However, the legacy of these giants remains in the fossil record, including giant dragonfly-like insects with wingspans of 70 centimeters. The evolution of insect wings has been a subject of debate, with theories suggesting they came from modified gills, flaps on the spiracles, or an appendage at the base of the legs. More recently, entomologists have favored the evolution of wings from lobes of the notum or the pleuron. In the Carboniferous age, the dragonfly-like Meganeura had as much as a 70 centimeters wide wingspan. The appearance of gigantic insects is consistent with high atmospheric oxygen at that time, as the respiratory system of insects constrains their size. The largest flying insects today are much smaller, with the largest wingspan belonging to the white witch moth, at approximately 28 centimeters. Unlike birds, small insects are swept along by the prevailing winds, although many larger insects migrate. Aphids are transported long distances by low-level jet streams, a testament to the power of flight in the insect world.
What is the origin of the word insect and what does it mean?
The word insect comes from a Latin root meaning cut, a description that has defined these creatures for over two millennia. Pliny the Elder introduced the term to the Latin world by calquing the Ancient Greek word entomon, which Aristotle used to describe life forms with notched bodies.
When did the oldest fossil insect appear and what was it called?
The oldest fossil that may be a primitive wingless insect is Leverhulmia from the Early Devonian Windyfield chert, dating back to a time when the first forests were just beginning to take shape. These early ancestors were small, soft-bodied, and fragile, yet they possessed a chitinous exoskeleton that would become the defining armor of the class.
How large could insects grow during the Carboniferous age and what species is an example?
In the Carboniferous age, the dragonfly-like Meganeura had a wingspan of up to 70 centimeters, a giant that ruled the skies of the Paleozoic Era. These ancient giants were possible because the atmosphere was thick with oxygen, allowing insects to grow to sizes that seem impossible today.
What is the value of insect pollination of crops and fruit trees in the US as of 2021?
The value of insect pollination of crops and fruit trees was estimated in 2021 to be about 34 billion dollars in the US alone. Most flowering plants require an animal to do the transportation, and the majority of pollination is by insects.
How many insect species extinctions have been recorded since 1500 and what is the current rate of population decline?
At least 66 insect species extinctions have been recorded since 1500, many of them on oceanic islands. A larger 2020 meta-study, analyzing data from 166 long-term surveys, suggested that populations of terrestrial insects are indeed decreasing rapidly, by about 9% per decade.
Insects are the earliest organisms to produce and sense sounds, but their true mastery lies in the chemical language they have developed. Many insects have evolved chemical means for communication, using semiochemicals derived from plant metabolites to attract, repel, or provide information. Pheromones are used for attracting mates of the opposite sex, for aggregating conspecific individuals, and to mark a trail. Allomones benefit their producer by the effect they have upon the receiver, while kairomones benefit the receiver instead of their producer. The use of scents is especially well-developed in social insects, where complex chemical signals coordinate the activities of thousands of individuals. Some insects, such as the firefly Photuris, mimic the flashing of female Photinus species to attract males, which are then captured and devoured. This is a form of aggressive mimicry that highlights the deadly nature of insect communication. Chemical defense is common among Coleoptera and Lepidoptera, usually being advertised by bright warning colors, as in the monarch butterfly. As larvae, they obtain their toxicity by sequestering chemicals from the plants they eat into their own tissues. Some manufacture their own toxins, and predators that eat poisonous butterflies and moths may vomit violently, learning not to eat insects with similar markings. This is the basis of Müllerian mimicry, where inedible species, such as wasps and bees, resemble each other to reduce the sampling rate by predators.
The Social Superorganism
Social insects, such as termites, ants, and many bees and wasps, are eusocial, living together in large, well-organized colonies of genetically similar individuals that are sometimes considered superorganisms. In these colonies, reproduction is largely limited to a queen caste, while other females are workers, prevented from reproducing by worker policing. Honey bees have evolved a system of abstract symbolic communication where a behavior is used to represent and convey specific information about the environment. In this communication system, called dance language, the angle at which a bee dances represents a direction relative to the sun, and the length of the dance represents the distance to be flown. Bumblebees too have some social communication behaviors, and Bombus terrestris, for example, more rapidly learns about visiting unfamiliar, yet rewarding flowers, when they can see a conspecific foraging on the same species. Only insects that live in nests or colonies possess fine-scale spatial orientation. Some can navigate unerringly to a single hole a few millimeters in diameter among thousands of similar holes, after a trip of several kilometers. In philopatry, insects that hibernate are able to recall a specific location up to a year after last viewing the area of interest. A few insects seasonally migrate large distances between different geographic regions, as in the continent-wide monarch butterfly migration, a journey that spans thousands of miles and involves multiple generations.
The Silent Pollinators
Pollination is the process by which pollen is transferred in the reproduction of plants, thereby enabling fertilization and sexual reproduction. Most flowering plants require an animal to do the transportation, and the majority of pollination is by insects. Because insects usually receive benefit for the pollination in the form of energy-rich nectar, it is a mutualism. The various flower traits, such as bright colors and pheromones that coevolved with their pollinators, have been called pollination syndromes, though around one third of flowers cannot be assigned to a single syndrome. The value of insect pollination of crops and fruit trees was estimated in 2021 to be about 34 billion dollars in the US alone. Insects play many critical roles in ecosystems, including soil turning and aeration, dung burial, pest control, and wildlife nutrition. For instance, termites modify the environment around their nests, encouraging grass growth, and many beetles are scavengers. Dung beetles recycle biological materials into forms useful to other organisms. Insects are responsible for much of the process by which topsoil is created. Without these tiny architects, the world would be a very different place, and the complex web of life that depends on flowering plants would collapse.
The Human Connection
Humans have long regarded many insects as pests, especially those that damage crops, and have attempted to control them using insecticides and other techniques. Other pests include insects like termites that damage wooden structures, herbivorous insects such as locusts, aphids, and thrips that destroy agricultural crops, or like wheat weevils that damage stored agricultural produce. Farmers have often attempted to control insects with chemical insecticides, but increasingly rely on biological pest control, which uses one organism to reduce the population density of a pest organism. This is a key element of integrated pest management, and biological control is favored because insecticides can cause harm to ecosystems far beyond the intended pest targets. Insects are consumed as food in 80% of the world's nations, by people in roughly 3,000 ethnic groups. In Africa, locally abundant species of locusts and termites are a common traditional human food source. Some, especially deep-fried cicadas, are considered to be delicacies. Insects have a high protein content for their mass, and some authors suggest their potential as a major source of protein in human nutrition. In most first-world countries, however, entomophagy is taboo, yet they are recommended by armed forces as a survival food for troops in adversity. Because of the abundance of insects and a worldwide concern of food shortages, the Food and Agriculture Organization of the United Nations considers that people throughout the world may have to eat insects as a food staple.
The Declining World
At least 66 insect species extinctions have been recorded since 1500, many of them on oceanic islands. Declines in insect abundance have been attributed to human activity in the form of artificial lighting, land use changes such as urbanization or farming, pesticide use, and invasive species. A 2019 research review suggested that a large proportion of insect species is threatened with extinction in the 21st century, though the details have been disputed. A larger 2020 meta-study, analyzing data from 166 long-term surveys, suggested that populations of terrestrial insects are indeed decreasing rapidly, by about 9% per decade. This decline is a cause for concern, as insects play many critical roles in ecosystems, including soil turning and aeration, dung burial, pest control, and pollination. The loss of insects would have a cascading effect on the entire ecosystem, from the smallest plants to the largest predators. Insects are the most diverse group of animals, with more than a million described species, and they represent more than half of all animal species. The loss of even a small percentage of these species could have devastating consequences for the planet. The world is losing its silent architects, and the consequences of this loss are only beginning to be understood.