The last nymphal instar climbs on a blade of grass and molts outside water to give rise to adult. Wings develop as buds externally on the thorax. The larvae breathe with tracheal gills attached on the tip of abdomen. Examples are: Odonata (dragon and damsel flies), Ephemeroptera (may flies) and Plecoptera (stone flies). Such nymphs are called NAIADS which are generally carnivorous in habit. Those insects whose larvae are aquatic while adults are a flying terrestrial insects show differences in the morphology of their nymphal stages owing to their aquatic habitat. These insects do not show any dormant stage during development and nymphs are active throughout their growth stage. Hemimetabola includes two categories as given below. The examples are: grasshoppers, locusts, cockroaches, dragon flies, Mayflies, earwigs, lice, bugs, thrips etc. Nymphs generally live in the same environment as the adults. The transformation takes place in the growth of wings as external buds and development of secondary sexual characters. There are 15 orders of insects which demonstrate this kind of metamorphosis in which juveniles are similar to the adults and there is a gradual change from nymphs to adults. Some biologists do not consider it as metamorphosis or called it Anamorphosis as there is little change during development. The insects are wingless both in larval as well as in adult stages. These nymphs live in the same environment as the adult and feed on the same diet as the adult. As the nymph grows and molts its segments in abdomen increase gradually to become 11 in adult. The nymph upon hatching from the egg is similar to the adult in general morphology but there are only 8 abdominal appendages and cerci are lesser in number. This type of metamorphosis occurs in orders Protura, Diplura, Collembola and Thysanura that include insects such as telson-tails, campodeids, spring tails and silverfish. Insects show various types of metamorphosis as described below.ġ. When the larvae undergo considerable change to become adults it is called metamorphosis. Adults are generally quite different from the larval forms. Insect life cycle is generally complex involving several stages of the larval and pupal development.
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