Insects Essay

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Insects are invertebrates that are divided into 36 groups called Phyla. Phylum Arthropoda includes the class Insecta, which is further subdivided into 29 orders. Diptera (flies), Coleoptera (beetles), Phasmida (stick insects), Dictyoptera (cockroaches and praying mantids), Hymenoptera (wasps, ants, and bees), and Lepidoptera (butterflies and moths) are some examples. About 95 percent of all the animal species on earth are insects. They have a very small body, can survive on very small amount of food, and can multiply very quickly.

All insects have three body parts: a head, thorax, and abdomen. They have six jointed legs, two antennae to perceive the world around them and an exoskeleton (outside skeleton). The multilayered exoskeleton, which is composed of hardened layers of protein and chitin, form their body shape. The exoskeleton has the capacity to protect the insect from the environment or natural enemies and has several sense organs for detecting light, pressure, sound, temperature, wind, and smell, which makes them very successful survivors. Most insects have one or two pairs of wings, but wings are not an essential characteristic to be classified as insects.

Insects use their head for eating, sensing things, and gathering information. They use their antennae to feel, smell, and taste. The thorax is where three pairs of jointed legs, and in many insects, one or two pairs of wings are located. The abdomen has the organs of digestion and reproduction. Insects have open circulatory system and its body fluid circulates around inside the exoskeleton. It has a heart and a few blood vessels, but blood simply flows around inside the body cavity.

Air enters through spiracles located in the exoskeleton and circulates through the breathing tubes, which spread out everywhere in the body. The digestive system is very simple, consisting of a long tube. This tube is usually divided into three parts. The brain is very small and is located in the head, and processes information, but some information is also processed at nerve centers at different places in the body. The nervous system sends messages from the sense organs to and from the brain. Insects have compound eyes, containing thousands of sixsided lenses, each of which can work independently. There are some insects that can perceive ultraviolet light, which is invisible to humans.

Insect Types

Five groups of insects are based on their food habits and nutrition intake. Scavenger insects feed on waste material such as decomposed animal and plant material, and even products from other insects like oils and waxes.

Omnivores such as cockroaches seem to eat just about anything, from bookbindings to fellow insects. Herbivore insects eat leaves, and include caterpillars, butterflies, and bees. Carnivore insects are blood suckers and also feed on other insects.

Parasitic insects obtain nutrition from their hosts. The true parasites, like fleas and lice-as well as parasitoids-are only parasitic as larvae.

Positive Effects on Environment

Insects contribute to maintain ecological balance. Plants and insects are important to each other’s existence. Insects transmit pollen from plant to plant as they feed on the plant’s nectar. Insect diversification may have led to the radiation of flowering plants.

Insects keep earth clean by means of an efficient recycling system, because of their ability to reprocess dead plants and animals. Several insects work as decomposers. The carpenter ants, wood-boring beetles, and termites reduce logs, limbs, and leaves, which fall on the forest floor. Insects also eliminate animal waste, but in the case of fly larvae, it can also be a way of spreading disease. Decomposer insects can also improve the texture and quality of soil by adding humus (decayed vegetable and animal matter). The humus provides nutrients for the plants and improves the soil’s ability to retain water. Some ant species of Panama build their nest in the shape of an upside-down arrowhead to let the rain slide off, showing an adaptation to nature. These ants are natural enemies of termites and protect the trees against their insidious invasion. Humans are also greatly benefited by insects, as they produce honey, silk, wax, and other products.

Detrimental Effects

Insects are also major pests of humans and domesticated animals because they destroy crops and carry different types of diseases as transmitters or vectors. The World Health Organization identifies eight major insect-borne diseases. Sleeping sickness is transmitted by the tsetse fly, with 55 million people in Africa at risk. Leishmanisis causes elephantitis and disfigures legs, arms, and genitals, and is transmitted by culex mosquitoes that infect about 120 million people in Africa, South and South East Asia, the Pacific Islands, and Latin America. Chagas disease (American trypnosomiasis) is caused by T. cruzi, transmitted to humans by a bloodsucking traitomine bug, and infects 18 million people in the Americas, excluding Canada. Malaria is caused by a bite from an infected female mosquito when human blood is infected with malarial parasite, and is endemic to about 90 countries, mainly in Africa and South and East Asia. Dengue fever is caused by viruses transmitted by the andes aegypti mosquito, affecting 100 countries except Europe with 20 million cases annually. Yellow fever virus is carried by haemagogus mosquitoes and transmitted to humans in tropical South America and Africa, causing illness to 200,000 people annually. The mosquito vector culex tritaeniorhynous, associated with rice-producing areas of the world, transmits the Japanese encephalitis virus to humans, causing sickness to an estimated 43,000 occurrences. And Plague, which caused Black Death and wiped out about one-third to half of the European population in the 14th century, is caused by the bacterium yersinia pestis. Rat fleas carry this pestis to other rats and humans. The world is mostly free of this deadly disease now except for an occasional outbreak. Although misery delivered by insects to humans is tremendous, only 1 percent of the world’s insects are considered pests.

Changing climatic conditions resulting from global warming have enabled different disease-carrying insects, including mosquitoes, to survive and multiply in colder northern latitudes and higher elevations all over the world, which increases the possibility of spreading tropical diseases to temperate regions. Global warming has affected the population of a particular migratory bird, the pied flycatcher, and subsequently its prey, the caterpillar. The flycatchers’ population has plummeted to an astonishing 90 percent over the past two decades in some parts of the Netherlands. When hatchlings emerge, the parents feed them mostly with caterpillars, which are most abundant during an approximately three-week period after Dutch plants have flowered. However, due to warming average temperatures, plants in some parts of the Netherlands flower an average of 16 days earlier in the spring, knocking the prime caterpillar season off by nearly a week. This creates inadequate nourishment, leading to the death of birds and falling population.

Bibliography: 

  1. D. Imms, Insects Natural History (Collins Cear-Type Press, 1973);
  2. D. Lemonick, “Bye Bye Birdies,” Time (May 15, 2006);
  3. V.A. Little, General and Applied Entomology (Harper & Row, 1963);
  4. World Health Organization, The World Health Report 1996, Fighting Disease Fostering Development (WHO, 1996).

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