|MadSci Network: Zoology|
Dear Maryam thank you for your question. Biologists call the immature forms (that can not reproduce) of insects "larva". Thus in principle any and every insect goes through a larval stage. But I am quite sure, that is not what you wanted to know. Therefore, let me give you some background information about insect development, and then I try to answer your question again. In nearly all insects growth involves a metamorphosis, that is, a transformation in form and in way of life. Insects in which the adult form is only seen after the last or next-to-last molt of the young are called "holometabolous". Beetles, flies, mosquitoes, moths and butterflies are examples for holometabolous insects. Complete, or indirect, metamorphosis is characteristic of over 80% of all insect species and has four stages: egg, larva, pupa, and adult. The wingless, wormlike larva (in many species called a grub or a caterpillar) is completely unlike the adult, and its chief activities are eating and growing. Only the simple eyes are present, and the mouth is the chewing type, even in species whose adults have other kinds of mouthparts. After several molts the larva enters a quiescent stage called the pupa; the pupa does not eat and usually does not move, but within the exoskeleton a major transformation occurs that involves the reorganization of organ systems as well as the development of such adult external structures as wings and compound eyes. In some insects the pupa is enclosed in a protective case, called the cocoon, built by the larva just before pupation. When the transformation is complete the final molt occurs: the adult emerges, its wings fill with blood and expand, and the new exoskeleton hardens. The chief function of the adult is propagation; in some species it does not eat. Incomplete, or gradual, metamorphosis is seen in members of fewer insect orders. The larva, often called a nymph (or, if aquatic, a naiad) is usually similar in form to the adult, but lacks wings. The wings begin as external bumps on the larva, and the adult emerges from the last molt without having undergone a pupal stage. Insects in which the young look like little versions of the adults are called "hemimetabolous". Grasshoppers, aphids, cicadas, termites and cockroaches are examples for hemimetabolous insects. Thus - to answer your question now directly: if you observe a grashopper hatching out from its egg, you will see, that I looks like a perfect miniature version of the final adult grasshopper, just that it does not have any wings jet. With that you can be sure, that you observe a nymph (or larva) of a hemimetabolous insect. If it would be a holometabolous insect, it would like totally different from its adult form. (That is how the mealworm got its name - it looks much more like a worm than like the beetle that it will become later in life.) I hope that helps. If you want more information about this, any introductory book about insects should tell you about the different kinds of development with nice pictures as examples. If you do a search on the internet on the keywords "insect" and "metamorphosis" you certainly will get to many pages with good information on this subject. Have a good day Jurgen Ziesmann
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