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Insects first appeared on Earth in the late Silurian Period. The earliest insects had a simple 2-stage lifecycle in which miniature versions of the wingless adults emerged from eggs. Such insects are called Apterygotes. Modern day examples include silverfish, springtails and bristletails.

Winged insects probably first appeared in the late Devonian or lower carboniferous Period, when a 3-stage Exopterygote lifecycle evolved. In this case wingless nymphs emerge from eggs. As the nymphs feed and grow they periodically moult their skins. The stages between the moults are called instars. During the later instars the nymphs develop wing “buds”, but it is not until the final moult that fully developed wings are present. Examples of Exopterygotes include mayflies, dragonflies, stick and leaf insects, katydids, mantises, earwigs, cockroaches, lice, termites and shield bugs.

The most advanced insects, i.e. those with a 4-stage lifecycle, evolved in the late Carboniferous Period. These are known as Endopterygotes, examples of which include lacewings, scorpion flies, caddis flies, true flies, fleas, bees, wasps, ants, sawflies, beetles, butterflies and moths.

The lifecycle of butterflies was first unravelled in 1600 by Maria Sibyella Merian, who observed that they have 4 distinct phases of development : ovum, larva, pupa and imago ( adult ). Each stage of the lifecycle is sharply differentiated from the last but is ontogenetically dependent on it. Individuals carry genes which govern development at each stage of the lifecycle but different genes come into play at each stage. Adult butterflies for example carry caterpillar genes that are “switched off” and vice versa. Mutant genes control features that are only present during part of the lifecycle e.g. only adult butterflies have antennae, wings and a proboscis. Behavioural features such as mate location, copulation and migration are also controlled genetically by these mutant genes.