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Listen to part of a lecture in a biology class.

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Okay, let\'s talk about butterflies.

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As most of you probably know a butterfly undergoes radical changes in the course of its transformation from an egg to an adult butterfly.

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People have been fascinated by this metamorphosis for 1000s of years.

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The butterfly life cycle has four stages.

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The first stage is the egg; the second stage is the larva.

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That\'s what most people refer to as a caterpillar.

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The third stage is the pupa, and the fourth stage is the adult butterfly.

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So for the first stage, the female butterfly has to deposit her eggs on a plant that has a lot of edible leaves.

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That\'s because when the eggs hatch, the larva is basically eating machine.

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It needs tremendous amounts of food to sustain its rapid growth.

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Once it\'s grown to its full size, which takes about two or three weeks.

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The larva attaches itself to a twig or a blade of grass and becomes a pupa.

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The pupa is encased in a hard outer shell.

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From the outside it may appear to be totally lifeless.

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But inside the shell, some pretty amazing transformations are taking place.

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The structure of the larva is breaking down

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And being replaced by the structure of an adult butterfly.

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If this process proceeds without any interruption

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an adult butterfly can emerge within two weeks

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but some pupae may remain dormant.

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That is, they may remain in a resting state for a lot longer than that

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and we\'ll talk more about that in a minute.

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When the adult butterfly emerges from the pupa, its wings dry out and harden

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and the transformation is complete, you then have a fully formed adult butterfly.

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Now, typically, a large group of butterflies from the same species will emerge at around the same time, say, in the spring.

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each one of these groups that emerge is called a brood that b, r, o, o, d.

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butterfly species in cooler climates, where the summers shorter

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generally produce only one brood per year.

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A nice example is the brown elfin butterfly.

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In the spring, the brown elfin females lay their eggs.

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In the summer, the eggs hatch and the larvae feed until they turn into pupae.

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During the fall and winter, the pupa rests, and then the following spring, the next brood emerges.

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so one brood per year.

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But in warmer climates, most butterfly species will produce two broods per year.

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the second brood emerging late in the summer.

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Now what\'s interesting is that the same species can be single brooded in cooler climate zones and double brooded in warmer climate zones.

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And what\'s also interesting is that the number of broods produced is often tied in with the size of the butterflies.

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In other words, you can have the same species and when it produces just one brood.

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the butterflies that emerge are often bigger than when that species produces two broods per year.

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you know, maybe in a warmer climate zone.

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So it\'s often the case that the fewer the broods.

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the bigger the butterflies.

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The more broods, the smaller the butterflies.

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And speaking of size, when you see a small butterfly.

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It\'s not a baby butterfly.

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it\'s a small, full sized adult.

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That\'s because butterflies reach their full adult size before they emerge from their shell.

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Now you have a lot of possible variations in butterfly life cycles and variations can give a species new avenues to develop and evolve.

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It\'s possible, for example.

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that at some time, you\'ll have a unique set of circumstances.

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maybe some unusual environmental conditions.

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and the next thing you know, you have a brown elfin butterfly flying in the fall.

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Just because we haven\'t yet observed a brown elf and butterfly flying in the fall doesn\'t mean it can\'t happen.

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I mean, we\'re now discovering that even in warmer climate zones.

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some pupae may remain dormant for two, three or even four years

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if there are unfavorable conditions, say a drought or a flood.

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