Insects (1953)

[Music] animals that repeat man for supremacy on earth insects are our nearest rivals and deserve a close look numbering over a million species insects are the largest single group of animals in the world in this film we shall consider what insects are how they differ from one another and from some of their close relatives how they live and reproduce and how some are injurious to man and others beneficial lobsters spiders and centipedes are related to insects all are members of a group called arthropods characterized by a next segment Advani and jointed appendages but why are insects put in a special class what distinguishes them from other animals all insects have certain characteristics in common for instance three distinct body parts an abdominal a thorax and a head on the head are important organs like the eyes the antennae and the food gathering organs on the thorax the grasshopper has three pairs of legs no insect has more than three pairs of legs also on the thorax most insects have two pairs of wings the skeleton of an insect is outside its body and is called an exoskeleton breathing is accomplished through pores called spiracles along the side of the body but there are differences among insects too and their scientific names often denote identifying features for instance butterflies and moths are members of a group called Lepidoptera which indicates that they have scales on their wings wasps are classified as Hymenoptera meaning insects with thin membranous wings beetles are Coleoptera flies are Diptera meaning to wing they are an exception in the insect world since most insects have four wings grasshoppers are Orthoptera although some fly well they have hind legs fitted for leaping their straight four wings cover fan-shaped under wings some animals look like insects but are not set to body regions and four pairs of legs therefore the insects neither is a centipede and as more than three pairs of legs insects developed from young to adult in three different ways they all start from eggs of course silverfish illustrate the first method the young are much like the adult except in size there is no metamorphosis but while the creature that comes out of a grasshopper egg case looks like the adult grasshopper it differs in that the young called nymph has no wings as it develops it gets too large for its exoskeleton and has to shed it in order to grow it gets wings in its final molt this second kind of development is called gradual or incomplete metamorphosis which means no basic change in structure from nymph to adult the same applies to aphids but during part of the year females are known as stem mothers when they give birth to living young without meeting this reproductive process is known as male here in the fall and mating females lay eggs from which their mothers hatch in the spring complete metamorphosis the third way of insect development shows four distinct changes from egg to adult the cycle starts when for example an adult Mexican bean beetle lays a cluster of eggs larvae hatch from the eggs the larval stage is mainly a feeding stage mature larvae change to pupae here we see this change take place by time-lapse photography and the final change from few put to adult complete metamorphosis always takes place in four stages eggs come first and then larvae third camp you pee forth adults why do insects compete so successfully one reason is that insects are cold-blooded and don't have to food energy to keep a constant body temperature their small size helps also this corn earworm needs little food to survive these ambush bugs get along well because their color and shape make it difficult for enemies to see them and these tree hoppers look like small thorns on the branches where they hide then to foods that insects eat are usually plentiful man himself plants many crops which insects like this corn borer find much to their taste insects also thrive because they reproduce rapidly each insect generation is numerous and many insects have several generations each season a single pair of house flies may have millions of descendants in one season insect competition with man is serious America's annual loss to insects is in the billions of dollars grasshoppers alone eat millions of dollars worth of food each year they not only strip our cattle lands of grass but they devour our corn from without while corn borers and corn ear worms devour it from within and weevils feed on the harvested corn that the farmer manages to save from the other insects other millions of dollars are lost annually to the boll weevil which ruins our cotton before the harvest countless other insects such as tent caterpillars blister beetles and potato beetles feed on our fruit and vegetable crops but insects to more than devour our foods moth larvae feed on our woman's termites destroy foundations made of wood disease bearing life's feed on human blood and so do mosquitoes natural trolls help us in our fight against insect pests birds consumed tons of insects fish eat millions of insect larvae bacteria infect and destroy summat these Japanese beetle larvae show three stages of a bacterial disease that is generally fatal insects prey on each other the robber fly sucks the body juices from its prey this hornworm covered with small silk cocoons is doomed to die a parasitic wasp laid its eggs within the hornworms body the larvae of such parasites grow up inside the bodies of their hosts and emerge to pupate and start a new life cycle but natural controls are not enough man must carry the fight against his insect enemies to survive and so to destroy the corn borer the farmer attacks with the plough to bury them alive with the corn stalks after the harvest to save our fruit crops insect poisons are sprayed by fruit growers the potato grower attacks by air with insecticide dust while the truck gardener scatters poison bait to kill insect enemies part of the war against mosquitoes is fought in the trenches which are done to drain and destroy their breeding places yes this is real war and in order to learn better how to combat insects trained investigators study insect life cycles and eating habits new poisons are developed to rid us of insect pests ants are mostly a nuisance but the cockroach spreads disease as well as ruining food this is an enemy of man one of the many insect enemies that consume our vegetables feed on food crops devour our grains destroy our cotton chew up our houses the clothes we wear and even drink our blood and while we slap and swat dig and plow experiment and dust millions more insects are hatching out all around us new hordes of insects to compete with the swelling population of mankind for the necessities of life but in our warfare against insect enemies we must be careful to recognize and protect our insect friends such as the bees which pollinate our flowers and our fruit and vegetable crops other insects such as the ambush bug the praying mantis and parasites that attack harmful insects are also helpful to man without fruit flies or other insects the study of genetics would be unbelievably handicapped yes some insects are helpful but only true study can man know which insects to befriend and which to fight it is important to know for insects are man's closest competitor for supremacy on the earth [Music] you