MadSci Network: Zoology

Re: by observing a grasshopper as it hatches out of its egg, how could you -

Date: Wed Dec 13 11:00:33 2000
Posted By: Jurgen Ziesmann, Post-doc Biology and Ecological Chemistry
Area of science: Zoology
ID: 969997638.Zo

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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